Patent Publication Number: US-2023156369-A1

Title: Solid-state imaging device, method for manufacturing solid-state imaging device, and electronic apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a solid-state imaging device, a method for manufacturing a solid-state imaging device, and an electronic apparatus. 
     BACKGROUND 
     Solid-state imaging devices (image sensors) including photoelectric conversion elements for detecting light and generating charges are embodied as CMOS (complementary metal oxide semiconductor) image sensors, which have been in practical use. The CMOS image sensors have been widely applied as parts of various types of electronic apparatuses such as digital cameras, video cameras, surveillance cameras, medical endoscopes, personal computers (PCs), mobile phones and other portable terminals (mobile devices). 
     The CMOS image sensor includes, for each pixel, a photodiode (a photoelectric conversion element) and a floating diffusion (FD) amplifier having a floating diffusion (FD). The mainstream design of the reading operation in the CMOS image sensor is a column parallel output processing of selecting one of the rows in the pixel array and reading the pixels in the selected row simultaneously in the column output direction. 
     Each pixel of the CMOS image sensor generally includes, for one photodiode for example, four active elements: a transfer transistor serving as a transfer element, a reset transistor serving as a reset element, a source follower transistor serving as a source follower element (an amplification element), and a selection transistor serving as a selection element. 
     In recent years, the increase in number of pixels in the CMOS image sensors lead to an enhanced demand for a reduction in size of the pixels. To deal with this demand, multiple-pixel sharing technique has been proposed, according to which one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are shared between a plurality of pairs of a photodiode and a transfer transistor. 
       FIG.  1    is a circuit diagram showing an example of the pixels of a CMOS image sensor having a two-pixel sharing configuration in which one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are shared by two sets of a photodiode and a transfer transistor (see, for example, Patent Literature 1). 
     A sharing pixel PXL 1  shown in  FIG.  1    includes, for example, a first photodiode PD 0 , which serves as a first photoelectric conversion element, and a second photodiode PD 1 , which serves as a second photoelectric conversion element. In the sharing pixel PXL 1 , the first and second photodiodes PD 0  and PD 1  share a floating diffusion FD, which serves as an output node. 
     The first and second photodiodes PD 0  and PD 1  perform photoelectric conversion to generate charges and store the generated charges in an integration period. A first transfer transistor TG 0 -Tr is connected between the storage part of the first photodiode PD 0  and the floating diffusion FD. A second transfer transistor TG 1 -Tr is connected between the storage part of the second photodiode PD 1  and the floating diffusion FD. 
     The sharing pixel PXL 1  includes, for one floating diffusion FD serving as the output node, one reset transistor RST-Tr serving as a reset element, one source follower transistor SF-Tr serving as a source follower element, and one selection transistor SEL-Tr serving as a selection element. 
       FIG.  2    is a simplified plan view showing a two-pixel sharing scheme, specifically showing, as an example, how two sets of a photodiode and a transfer transistor, one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are arranged. 
     The sharing pixel PXL 1  has a rectangular region RCT 1  where the elements are formed. The rectangular region RCT 1  can be divided into a central region CTAR 1  positioned in the center, and a first region FSAR 1  and a second region SCAR 1  sandwiching the central region CTAR 1  therebetween (in the Y direction). 
     In the central region CTAR 1 , the floating diffusion FD is formed in the X- and Y-direction-wise central portion thereof, the reset transistor RST-Tr is formed on the right side of the floating diffusion FD in the X direction, and the source follower transistor SF-Tr and the selection transistor SEL-Tr are formed on the left side of the floating diffusion FD in the X direction. The relative positions represented by the terms such as left and right can be only example and modified in any other manners than the illustrated example. 
     The first photodiode PD 0  and the first transfer transistor TG 0 -Tr are adjacent to each other in the first region FSAR 1 . As shown in the example of  FIG.  2   , the first transfer transistor TG 0 -Tr is shaped like a rectangle, arranged closer to the central region CTAR 1 , and connected to the floating diffusion FD. 
     In the second region SCAR 1 , the second photodiode PD 1  and the second transfer transistor TG 1 -Tr are formed. As shown in the example of  FIG.  2   , the second transfer transistor TG 1 -Tr is arranged closer to the central region CTAR 1  and connected to the floating diffusion FD. 
     The configuration shown in  FIGS.  1  and  2    enables two pixels to share their pixel components, so that the photodiode PD per pixel can have a maximized size. This can contribute to reduce the size of the pixels while the sensitivity and full well capacity remain unchanged. 
       FIG.  3    is a circuit diagram showing an example of the pixels of a CMOS image sensor pixel having a four-pixel sharing configuration in which one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are shared by four sets of a photodiode and a transfer transistor (see, for example, Patent Literature 2). 
     A sharing pixel PXL 2  shown in  FIG.  3    includes, in addition to the components of the pixel PXL 1  shown in  FIG.  1   , a third photodiode PD 2 , which serves as a third photoelectric conversion element, and a fourth photodiode PD 3 , which serves as a fourth photoelectric conversion element. More specifically, in the sharing pixel PXL 2 , the first, second, third and fourth photodiodes PD 0 , PD 1 , PD 2  and PD 3  share a floating diffusion FD, which serves as an output node. 
     The first, second, third and fourth photodiodes PD 0 , PD 1 , PD 2  and PD 3  perform photoelectric conversion to generate charges and store the generated charges in the respective integration periods. A first transfer transistor TG 0 -Tr is connected between the storage part of the first photodiode PD 0  and the floating diffusion FD. A second transfer transistor TG 1 -Tr is connected between the storage part of the second photodiode PD 1  and the floating diffusion FD. A third transfer transistor TG 2 -Tr is connected between the storage part of the third photodiode PD 2  and the floating diffusion FD. A fourth transfer transistor TG 3 -Tr is connected between the storage part of the fourth photodiode PD 3  and the floating diffusion FD. 
       FIG.  4    is a simplified plan view showing a first example of the four-pixel sharing configuration, based on the same concept as the configuration shown in  FIG.  2   , specifically showing how four sets of a photodiode and a transfer transistor, one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are arranged. 
     The sharing pixel PXL 2  has a rectangular region RCT 2  where the elements are formed. The rectangular region RCT 2  can be divided into a central region CTAR 2  positioned in the center, and a first region FSAR 2  and a second region SCAR 2  sandwiching the central region CTAR 2  therebetween (in the Y direction). 
     In the central region CTAR 2 , the floating diffusion FD is formed in the X- and Y-direction-wise central portion thereof, the reset transistor RST-Tr is formed on the right side of the floating diffusion FD in the X direction, and the source follower transistor SF-Tr and the selection transistor SEL-Tr are formed on the left side of the floating diffusion FD in the X direction. The relative positions represented by the terms such as left and right can be only example and modified in any other manners than the illustrated example. 
     In the first region FSAR 2 , the first photodiode PD 0 , the first transfer transistor TG 0 -Tr, the third photodiode PD 2  and the third transfer transistor TG 2 -Tr are adjacent to each other. In the example shown in  FIG.  4   , the first photodiode PD 0  and the first transfer transistor TG 0 -Tr are formed in the left part (left half) of the first region FSAR 2 , and the third photodiode PD 2  and the third transfer transistor TG 2 -Tr are formed in the right part (right half) of the first region FSAR 2 . The first and third transfer transistors TG 0 -Tr and TG 2 -Tr are shaped like a rectangle, arranged closer to the central region CTAR 2  and connected to the floating diffusion FD. 
     In the second region SCAR 2 , the second photodiode PD 1 , the second transfer transistor TG 1 -Tr, the fourth photodiode PD 3  and the fourth transfer transistor TG 3 -Tr are adjacent to each other. In the example shown in  FIG.  4   , the second photodiode PD 1  and the second transfer transistor TG 1 -Tr are formed in the left part (left half) of the second region SCAR 2 , and the fourth photodiode PD 3  and the fourth transfer transistor TG 3 -Tr are formed in the right part (right half) of the second region SCAR 2 . The second and fourth transfer transistors TG 1 -Tr and TG 3 -Tr are shaped like a rectangle, arranged closer to the central region CTAR 2 , and connected to the floating diffusion FD. 
     The configuration shown in  FIGS.  3  and  4    enables four pixels to share their pixel components, so that the photodiode PD per pixel can have a maximized size. This can contribute to reduce the size of the pixels while the sensitivity and full well capacity remain unchanged. 
       FIG.  5    is a simplified plan view showing a second example of the four-pixel sharing, specifically showing how the four sets of a photodiode and a transfer transistor, one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are arranged. 
     A sharing pixel PXL 3  shown in  FIG.  5    has a configuration relating to a modification example of the four-pixel sharing, with eight pixels sharing two floating diffusions FD (see, for example, Patent Literature 3). The sharing pixel PXL 3  shown in  FIG.  5    has, in comparison with the four-pixel sharing configuration shown in  FIG.  4   , a first light receiving region RLT 1  and a second light receiving region RLT 2  where four photodiodes PD 0  to PD 3  and transfer transistors TG 0 -Tr to TG 3 -Tr are formed. 
     The sharing pixel PXL 3  further includes a first group of transistor GTR 1  and a second group of transistors GTR 2 . The first group of transistors GTR 1  includes a source follower transistor SF Tr and a selection transistor SEL-Tr. The second group of transistors GTR 2  includes a reset transistors RST 1 -Tr and a dummy reset transistor RST 2 -Tr. 
     Although one reset transistor RST-Tr is sufficient, the second group of transistors GTR 2  includes the dummy reset transistor RST 2 -Tr to allow the first and second groups of transistors GTR 1  and GTR 2  have symmetry in layout. 
     In the sharing pixel PXL 3  with the above configuration, symmetry is exhibited between the arrangement of the first light receiving region RLT 1  and the first group of transistors GTR 1  and the arrangement of the second light receiving region PLT 2  and the second group of transistors GTR 2 , with the floating diffusion FD being positioned at the optical center. This can contribute to reduce variability in sensitivity (output) characteristics between pixels of the same color. 
     RELEVANT REFERENCES 
     List of Relevant Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Application Publication No. 2007-81033 
         Patent Literature 2: Japanese Patent Application Publication No. 2006-302970 
         Patent Literature 3: Japanese Patent Application Publication No. 2018-93392 
       
    
     SUMMARY 
     In the above-described sharing pixel PXL 1  of the two-pixel sharing configuration, two pixels share their pixel components, so that the photodiode PD per pixel can have a maximized size. This can contribute to reduce the size of the pixels while the sensitivity and full well capacity remain unchanged. 
     The sharing pixel PXL 1  shown in  FIG.  2   , however, achieves only limited success in reducing the size of the pixels since the number of elements per sharing pixel is greater than in the sharing pixels PXL 2  and PXL 3  having the four-pixel sharing configuration. 
     The above-described sharing pixel PXL 2  of the four-pixel sharing configuration enables four pixels to share their pixel components, so that the photodiode PD per pixel can have a maximized size. This can contribute to reduce the size of the pixels while the sensitivity and full well capacity remain unchanged. 
     In the sharing pixel PXL 2  in  FIG.  4   , however, the floating diffusion FD has a large area. This disadvantageously increases the capacitance of the floating diffusion FD, which lowers the conversion gain and increases the noise. 
     In the sharing pixel PXL 3  shown in  FIG.  5   , for example, the photodiodes PD are radially arranged around the floating diffusion FD. If the photodiodes PD are arranged around the diffusion layer portion of the floating diffusion FD as shown in  FIG.  5   , the reset transistor RST-Tr cannot be adjacently placed. This requires that the diffusion layer portion of the floating diffusion FD be additionally provided in regions other than the center, for example, in the pixel separation region or at the edge of the pixels, to allow connection to be established through wiring. This in turn increases the junction capacitance and the wiring capacitance for electrical connection, which disadvantageously increases the capacitance (Cfd) of the FD node, reduces the conversion gain and causes the noise characteristics to drop. 
     Generally, the signal (overflow charges) exceeding the charges that can be stored on a certain photodiode PD may flow into adjacent pixels, which can result in mixing of charges (causing a false signal). To prevent this, the overflow charges from the certain photodiode are guided to flow into the connected floating diffusion FD before leaking out into adjacent pixels. When this configuration is applied, a false signal may be generated while the charges in the floating diffusion FD are being read out if charges leak into the floating diffusion from the pixels with which the certain photodiode shares the floating diffusion FD. For example, in the case of the Bayer array, if overflow charges of the G signal leak out while the R signal is being read out, the charges may mix together at the floating diffusion FD serving as an output node. 
     An object of the present invention is to provide a solid-state imaging device, a method for manufacturing a solid-state imaging device and an electronic apparatus that are capable of not only reducing the size of the pixels while the sensitivity and full well capacity remain unchanged but also preventing an increase in junction capacitance and wiring capacitance and an increase in the capacitance of the floating diffusion serving as an output node, to prevent a drop in conversion gain and eventually achieve improved noise characteristics. In addition, an object of the present invention is to provide a solid-state imaging device, a method for manufacturing a solid-state imaging device and an electronic apparatus that are capable of not only reducing the size of the pixels while the sensitivity and full well capacity remain unchanged but also preventing an increase in junction capacitance and wiring capacitance and an increase in the capacitance of the floating diffusion serving as an output node, to prevent a drop in conversion gain and eventually achieve improved noise characteristics, and also preventing the charges of different pixels from mixing together at the floating diffusion. 
     A first aspect of the present invention provides a solid-state imaging device including a pixel part having sharing pixels arranged therein, where each sharing pixel is configured to perform photoelectric conversion. The each sharing pixel has: at least three photoelectric conversion elements for storing therein, in an integration period, charges generated by photoelectric conversion; a plurality of transfer elements for individually transferring, in a transfer period following the integration period, the charges stored in the photoelectric conversion elements; a floating diffusion serving as an output node to which the charges stored in each of the photoelectric conversion elements are transferred through a corresponding one of the transfer elements; a reset element for resetting, in a reset period, the floating diffusion to a predetermined potential; and a source follower element serving as an output buffer part for converting the charges in the floating diffusion into a voltage signal at a level determined by an amount of the charges and outputting the voltage signal. One floating diffusion and one source follower element are shared between the photoelectric conversion elements and between the transfer elements, the floating diffusion is arranged at a center of an element formation region, and the photoelectric conversion elements are radially arranged around the floating diffusion, the floating diffusion has a first lateral part and a second lateral part facing each other, the source follower element is adjacent to the first lateral part of the floating diffusion in a first direction orthogonal to the first lateral part, and the reset element is adjacent to the second lateral part of the floating diffusion in the first direction, the floating diffusion and the source follower element are connected together via a wiring, any ones of the photoelectric conversion elements that are adjacent to each other in the second direction are spaced away from each other with a first spacing therebetween that allows at least the source follower element and the reset element to be formed, any ones of the photoelectric conversion elements that are adjacent to each other in the first direction are spaced away from each other with a second spacing therebetween that is less than the first spacing, and the transfer elements are provided to establish connection between (i) first-lateral-part edges of the floating diffusion at which the first lateral part terminates in the second direction and (ii) first edges of the photoelectric conversion elements facing the first-lateral-part edges, and between (I) second-lateral-part edges of the floating diffusion at which the second lateral part terminates in the second direction and (II) first edges of the photoelectric conversion elements facing the second-lateral-part edges. 
     A second aspect of the present invention provides a method for manufacturing a solid-state imaging device including a pixel part having sharing pixels arranged therein, where each sharing pixel is configured to perform photoelectric conversion. The each sharing pixel includes: at least three photoelectric conversion elements for storing therein, in an integration period, charges generated by photoelectric conversion; a plurality of transfer elements for individually transferring, in a transfer period following the integration period, the charges stored in the photoelectric conversion elements; a floating diffusion serving as an output node to which the charges stored in each of the photoelectric conversion elements are transferred through a corresponding one of the transfer elements; a reset element for resetting, in a reset period, the floating diffusion to a predetermined potential; and a source follower element serving as an output buffer part for converting the charges in the floating diffusion into a voltage signal at a level determined by an amount of the charges and outputting the voltage signal. One floating diffusion and one source follower element are shared between the photoelectric conversion elements and between the transfer elements, and the floating diffusion is arranged at a center of an element formation region, and the photoelectric conversion elements are radially arranged around the floating diffusion. The floating diffusion has a first lateral part and a second lateral part facing each other, the source follower element is adjacent to the first lateral part of the floating diffusion in a first direction orthogonal to the first lateral part, and the reset element is adjacent to the second lateral part of the floating diffusion in the first direction, the floating diffusion and the source follower element are connected together via a wiring, any ones of the photoelectric conversion elements that are adjacent to each other in the second direction are spaced away from each other with a first spacing therebetween that allows at least the source follower element and the reset element to be formed, any ones of the photoelectric conversion elements that are adjacent to each other in the first direction are spaced away from each other with a second spacing therebetween that is less than the first spacing, and the transfer elements are provided to establish connection between (i) first-lateral-part edges of the floating diffusion at which the first lateral part terminates in the second direction and (ii) first edges of the photoelectric conversion elements facing the first-lateral-part edges, and between (I) second-lateral-part edges of the floating diffusion at which the second lateral part terminates in the second direction and (II) first edges of the photoelectric conversion elements facing the second-lateral-part edges. 
     A third aspect of the present invention provides an electronic apparatus including a solid-state imaging device, and an optical system for forming a subject image on the solid-state imaging device. The solid-state imaging device includes a pixel part having sharing pixels arranged therein, where each sharing pixel is configured to perform photoelectric conversion. The each sharing pixel has: at least three photoelectric conversion elements for storing therein, in an integration period, charges generated by photoelectric conversion; a plurality of transfer elements for individually transferring, in a transfer period following the integration period, the charges stored in the photoelectric conversion elements; a floating diffusion serving as an output node to which the charges stored in each of the photoelectric conversion elements are transferred through a corresponding one of the transfer elements; a reset element for resetting, in a reset period, the floating diffusion to a predetermined potential; and a source follower element serving as an output buffer part for converting the charges in the floating diffusion into a voltage signal at a level determined by an amount of the charges and outputting the voltage signal. One floating diffusion and one source follower element are shared between the photoelectric conversion elements and between the transfer elements, the floating diffusion is arranged at a center of an element formation region, and the photoelectric conversion elements are radially arranged around the floating diffusion, the floating diffusion has a first lateral part and a second lateral part facing each other, the source follower element is adjacent to the first lateral part of the floating diffusion in a first direction orthogonal to the first lateral part, and the reset element is adjacent to the second lateral part of the floating diffusion in the first direction, the floating diffusion and the source follower element are connected together via a wiring, any ones of the photoelectric conversion elements that are adjacent to each other in the second direction are spaced away from each other with a first spacing therebetween that allows at least the source follower element and the reset element to be formed, any ones of the photoelectric conversion elements that are adjacent to each other in the first direction are spaced away from each other with a second spacing therebetween that is less than the first spacing, and the transfer elements are provided to establish connection between (i) first-lateral-part edges of the floating diffusion at which the first lateral part terminates in the second direction and (ii) first edges of the photoelectric conversion elements facing the first-lateral-part edges, and between (I) second-lateral-part edges of the floating diffusion at which the second lateral part terminates in the second direction and (II) first edges of the photoelectric conversion elements facing the second-lateral-part edges. 
     Advantageous Effects 
     The present invention can not only reduce the size of the pixels while the sensitivity and full well capacity remain unchanged but also prevent an increase in junction capacitance and wiring capacitance and an increase in the capacitance of the floating diffusion serving as an output node, to prevent a drop in conversion gain and eventually achieve improved noise characteristics. In addition, the present invention can not only reduce the size of the pixels while the sensitivity and full well capacity remain unchanged but also prevent an increase in junction capacitance and wiring capacitance and an increase in the capacitance of the floating diffusion serving as an output node, to prevent a drop in conversion gain and eventually achieve improved noise characteristics, and also prevent the charges of different pixels from mixing together at the floating diffusion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a circuit diagram showing an example of pixels of a CMOS image sensor having a two-pixel sharing configuration in which one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are shared by two sets of a photodiode and a transfer transistor. 
         FIG.  2    is a simplified plan view showing a two-pixel sharing scheme, specifically showing, as an example, how two sets of a photodiode and a transfer transistor, one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are arranged. 
         FIG.  3    is a circuit diagram showing an example of pixels of a CMOS image sensor having a four-pixel sharing configuration in which one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are shared by four sets of a photodiode and a transfer transistor. 
         FIG.  4    is a simplified plan view showing a first example of a four-pixel sharing configuration, specifically showing how four sets of a photodiode and a transfer transistor, one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are arranged. 
         FIG.  5    is a simplified plan view showing a second example of the four-pixel sharing configuration, specifically showing how four sets of a photodiode and a transfer transistor, one floating diffusion FD, one reset transistor, one source follower transistor, and one selection transistor are arranged. 
         FIG.  6    is a block diagram showing an example configuration of a solid-state imaging device according to a first embodiment of the present invention. 
         FIG.  7    is a circuit diagram showing an example of a sharing pixel of the solid-state imaging device relating to the first embodiment of the present invention. 
         FIGS.  8 A,  8 B and  8 C  illustrate examples of the configuration of a reading system of a column output from a pixel part of the solid-state imaging device according to the embodiment of the present invention. 
         FIG.  9    is a simplified sectional view showing an example configuration of the main part of the sharing pixel of the solid-state imaging device relating to the first embodiment of the present invention, or a charge integrating and transferring system including a pinned photodiode and a transfer transistor. 
         FIG.  10    is a simplified plan view showing, as an example, how four photodiodes, four transfer transistors, one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are arranged in a sharing pixel relating to the first embodiment. 
         FIG.  11    is a simplified sectional view showing the main part of the sharing pixel relating to the first embodiment and used to illustrate additional capacitance components added to the capacitance of the floating diffusion. 
         FIG.  12    is a simplified sectional view showing the main part of a sharing pixel of a comparative example that does not have the characteristic features of the sharing pixel relating to the first embodiment shown in  FIG.  11   , and used to illustrate additional capacitance components added to the capacitance of the floating diffusion. 
         FIGS.  13 A,  13 B and  13 C  show the layout of the solid-state imaging device relating to the first embodiment of the present invention, the layout of a first comparative example, and the layout of a second comparative example, which are compared against each other in terms of the FD node capacitance, wiring capacitance, their total capacitance, and size of the pixels. 
         FIG.  14    is a table showing the FD node capacitance, wiring capacitance, their total capacitance, and size of the pixels observed when the layout of the solid-state imaging device relating to the first embodiment of the present invention, the layout of the first comparative example and the layout of the second comparative example are applied. 
         FIG.  15    is a circuit diagram showing an example of a sharing pixel of a solid-state imaging device relating to the second embodiment of the present invention. 
         FIG.  16    is a simplified plan view showing, as an example, how four photodiodes, four transfer transistors, one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are arranged in the sharing pixel relating to the second embodiment. 
         FIG.  17    is a simplified sectional view showing an example configuration of a charge integrating and transferring system including a shutter gate transistor, or the main part of the sharing pixel relating to the second embodiment of the present invention. 
         FIG.  18    is a circuit diagram showing an example of a sharing pixel of a solid-state imaging device relating to a third embodiment of the present invention. 
         FIG.  19    is a simplified plan view showing, as an example, how four photodiodes, four transfer transistors, one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are arranged in a sharing pixel relating to the third embodiment. 
         FIG.  20    is a timing chart to illustrate an example sequence of operations for read-out performed in a read-out mode on sharing pixels in the solid-state imaging device relating to the third embodiment of the present invention. 
         FIG.  21    is a circuit diagram showing an example configuration of a sharing pixel of a solid-state imaging device  10 C relating to a fourth embodiment of the present invention. 
         FIGS.  22 A and  22 B  show sequences of operations to illustrate a global shutter read-out operation performed by the solid-state imaging device relating to the fourth embodiment, in comparison with a rolling shutter read-out operation. 
         FIGS.  23 A,  23 B and  23 C  show example timing charts to illustrate a rolling shutter read-out operation. 
         FIGS.  24 A,  24 B and  24 C  show example timing charts to illustrate a global shutter read-out operation. 
         FIG.  25    shows an example configuration of an electronic apparatus to which the solid-state imaging devices relating to the embodiments of the present invention can be applied. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be hereinafter described with reference to the drawings. 
     First Embodiment 
       FIG.  6    is a block diagram showing an example configuration of a solid-state imaging device relating to a first embodiment of the present invention. In this embodiment, a solid-state imaging device  10  is constituted by, for example, a CMOS image sensor. 
     As shown in  FIG.  6   , the solid-state imaging device  10  is constituted mainly by a pixel part  20  serving as an image capturing part, a vertical scanning circuit (a row scanning circuit)  30 , a reading circuit (a column reading circuit)  40 , a horizontal scanning circuit (a column scanning circuit)  50 , and a timing control circuit  60 . Among these components, for example, the vertical scanning circuit  30 , the reading circuit  40 , the horizontal scanning circuit  50 , and the timing control circuit  60  constitute a reading part  70  for reading out pixel signals. 
     According to the first embodiment, the solid-state imaging device  10  has pixels (or the pixel part  20 ) arranged in a matrix pattern in the pixel part  20 , as will be described in detail below. The pixels are configured such that at least three (in the present embodiment, four) photoelectric conversion elements (photodiodes) and transfer elements (transfer transistors) share one floating diffusion FD serving as an output node and one source follower element (source follower transistor) constituting an output buffer. The floating diffusion is placed at the center of the element formation area of the sharing pixel, and the photoelectric conversion elements are arranged radially (to form a square in the present embodiment) around the floating diffusion FD. 
     The sharing pixel of the solid-state imaging device  10  relating to the present embodiment has the following characteristic features to not only reduce the size of the pixels while the sensitivity and full well capacity remain unchanged but also prevent an increase in junction capacitance and wiring capacitance, preventing an increase in capacitance of the floating diffusion serving as an output node to prevent a drop in conversion gain, and eventually achieve improved noise characteristics. More specifically, the floating diffusion FD is shaped like a quadrilateral with all angles being 90 degrees (a rectangle in the present example) that has a first lateral part SDP 1  and a second lateral part SDP 2 , which are opposite to each other, when seen from above, as described below. In the central part CTR of the element formation area, the source follower element is adjacent to the first lateral part SDP 1  of the floating diffusion FD 10  in a first direction (for example, an X direction) orthogonal to the first lateral part SDP 1 , a reset element is adjacent to the second lateral part SDP 2  of the floating diffusion FD 10  in the first direction, and the floating diffusion FD 10  and the source follower element are connected through wiring. 
     Some of the photoelectric conversion elements are adjacent to each other in a second direction (for example, in a Y direction) and spaced away from each other with a first spacing D 1  therebetween that allows at least the source follower element and the reset element (MOS transistor) to be formed therein. Some of the photoelectric conversion elements are adjacent to each other in the first direction and arranged with a second spacing D 2  therebetween, which is less than the first spacing D 1 . Between (i) first-lateral-part edges SDT 11  and STD 12 , at which the first lateral part SDP 1  of the floating diffusion FD 10  terminates in the second direction, and (ii) first edges ED 111  and ED 112  of the photoelectric conversion elements facing the first-lateral-part edges SDT 11 , and between (I) second-lateral-part edges SDT 21  and SDT 22 , at which the second lateral part SDP 2  of the floating diffusion FD terminates in the second direction, and (II) first edges ED 121  and ED 122  of the photoelectric conversion elements facing the second-lateral-part edges SDT 21  and SDT 22 , the respective corresponding transfer elements are provided for establishing connection. Each transfer element extends to bridge a corresponding one of the first- and second-lateral-part edges of the floating diffusion FD and a corresponding one of the photoelectric conversion elements. 
     The solid-state imaging device  10  may be configured to be capable of operating in a global shutter mode. 
     The following first outlines the configurations and functions of the parts of the solid-state imaging device  10 , and then describes the configuration of the pinned photodiodes (PPD) and example arrangement of the elements in the sharing pixel. 
     &lt;Configurations of Pixel Part  20  and Sharing Pixel PXL 20 &gt; 
       FIG.  7    is a circuit diagram showing an example of the sharing pixel of the solid-state imaging device relating to the first embodiment of the present invention. 
     A sharing pixel PXL 20  shown in  FIG.  1    includes, for example, a first photodiode PD 10 , which is a first photoelectric conversion element, a second photodiode PD 11 , which is a second photoelectric conversion element, a third photodiode PD 12 , which is a third photoelectric conversion element, and a photodiode PD 13 , which is a fourth photoelectric conversion element. In the sharing pixel PXL 20 , the first, second, third and fourth photodiodes PD 10 , PD 11 , PD 12  and PD 13  share a floating diffusion FD 10 , which serves as an output node ND 10 . 
     The first, second, third and fourth photodiodes PD 10 , PD 11 , PD 12  and PD 13  perform photoelectric conversion to generate charges and store the generated charges in the respective integration periods. A first transfer transistor TG 10 -Tr is connected between a storage part PND 10  of the first photodiode PD 10  and the floating diffusion FD 10 . A second transfer transistor TG 11 -Tr is connected between a storage part PND 11  of the second photodiode PD 11  and the floating diffusion FD 10 . A third transfer transistor TG 12 -Tr is connected between a storage part PND 12  of the third photodiode PD 12  and the floating diffusion FD 10 . A fourth transfer transistor TG 13 -Tr is connected between a storage part PND 13  of the fourth photodiode PD 13  and the floating diffusion FD 10 . 
     The sharing pixel PXL 20  further includes, for one floating diffusion FD 10  serving as an output node ND 10 , one reset transistor RST 10 -Tr serving as a reset element, one source follower transistor SF 10 -Tr serving as a source follower element, and one selection transistor SEL 10 -Tr serving as a selecting element. 
     The first, second, third and fourth photodiodes PD 10 , PD 11 , PD 12  and PD 13  generate signal charges (electrons) in an amount determined by the amount of the incident light and stores the same. Description will be hereinafter given of a case where the signal charges are electrons and each transistor is an n-type transistor. However, it is also possible that the signal charges are holes or each transistor is a p-type transistor. 
     The photodiodes (PDs) in the sharing pixel PXL 20  are pinned photodiodes (PPDs). On a substrate surface for forming the photodiodes (PDs), there is a surface level due to dangling bonds or other defects, and therefore, a lot of charges (dark current) are generated due to heat energy, so that signals fail to be read out correctly. In the case of a pinned photodiode (PPD), a charge storage part of the photodiode (PD) is buried in the substrate to reduce mixing of the dark current into signals. 
     The first transfer transistor TG 10 -Tr of the sharing pixel PXL 20  is connected between the first photodiode PD 10  and the floating diffusion FD 10  and controlled by a control signal TG 10  applied to the gate thereof through a control line. The first transfer transistor TG 10 -Tr remains selected and in the conduction state during a transfer period PT in which the control signal TG 10  is at the high (H) level, to transfer to the floating diffusion FD 10  the charges (electrons) produced by the photoelectric conversion and then stored in the first photodiode PD 10 . After the first photodiode PD 10  and the floating diffusion FD 10  are reset to a predetermined reset potential, the first transfer transistor TG 10 -Tr enters the non-conduction state with the control signal TG 10  being set at the low (L) level, and the first photodiode PD 10  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the floating diffusion FD 10  as overflow charges through the overflow path under the first transfer transistor TG 10 -Tr. 
     The second transfer transistor TG 11 -Tr of the sharing pixel PXL 20  is connected between the second photodiode PD 11  and the floating diffusion FD 10  and controlled by a control signal TG 11  applied to the gate thereof through a control line. The second transfer transistor TG 11 -Tr remains selected and in the conduction state during a transfer period PT in which the control signal TG 11  is at the high (H) level, to transfer to the floating diffusion FD 10  the charges (electrons) produced by the photoelectric conversion and then stored in the second photodiode PD 11 . After the second photodiode PD 11  and the floating diffusion FD 10  are reset to a predetermined reset potential, the second transfer transistor TG 11 -Tr enters the non-conduction state with the control signal TG 11  being set at the low (L) level, and the second photodiode PD 11  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the floating diffusion FD 10  as overflow charges through the overflow path under the second transfer transistor TG 11 -Tr. 
     The third transfer transistor TG 12 -Tr of the sharing pixel PXL 20  is connected between the third photodiode PD 12  and the floating diffusion FD 10  and controlled by a control signal TG 12  applied to the gate thereof through a control line. The third transfer transistor TG 12 -Tr remains selected and in the conduction state during a transfer period PT in which the control signal TG 12  is at the high (H) level, to transfer to the floating diffusion FD 10  the charges (electrons) produced by the photoelectric conversion and then stored in the third photodiode PD 12 . After the third photodiode PD 12  and the floating diffusion FD 10  are reset to a predetermined reset potential, the third transfer transistor TG 12 -Tr enters the non-conduction state with the control signal TG 12  being set at the low (L) level, and the third photodiode PD 12  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the floating diffusion FD 10  as overflow charges through the overflow path under the third transfer transistor TG 12 -Tr. 
     The fourth transfer transistor TG 13 -Tr of the sharing pixel PXL 20  is connected between the fourth photodiode PD 13  and the floating diffusion FD 10  and controlled by a control signal TG 13  applied to the gate thereof through a control line. The fourth transfer transistor TG 13 -Tr remains selected and in the conduction state during a transfer period PT in which the control signal TG 13  is at the high (H) level, to transfer to the floating diffusion FD 10  the charges (electrons) produced by the photoelectric conversion and then stored in the fourth photodiode PD 13 . After the fourth photodiode PD 13  and the floating diffusion FD 10  are reset to a predetermined reset potential, the fourth transfer transistor TG 13 -Tr enters the non-conduction state with the control signal TG 13  being set at the low (L) level, and the fourth photodiode PD 13  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the floating diffusion FD 10  as overflow charges through the overflow path under the fourth transfer transistor TG 13 -Tr. 
     The reset transistor RST 10 -Tr is connected between a power supply line Vaapix of power supply voltage VAAPIX and the floating diffusion FD 10  and controlled by a control signal RST 10  applied to the gate thereof through a control line. The reset transistor RST 10 -Tr remains selected and in the conduction state during a reset period in which the control signal RST 10  is at the H level, to reset the floating diffusion FD 10  to the potential of the power supply line Vaapix of the power supply voltage VAAPIX. 
     The source follower transistor SF 10 -Tr and the selection transistor SEL 10 -Tr are connected in series between the power supply line Vaapix and a vertical signal line LSGN 10 . The gate of the source follower transistor SF 10 -Tr is connected to the floating diffusion FD 10 , and the selection transistor SEL 10 -Tr is controlled through a control signal SEL 10 . The source follower transistor SF 10 -Tr serving as a source follower element is connected at the source thereof to a reading node ND 11 , at the drain thereof to the power supply line Vaapix, and at the gate thereof to the floating diffusion FD 10 . The output node ND 10  constituting an output buffer part is connected to the vertical signal line LSGN 10  via the selection transistor SEL 10 -Tr. The selection transistor SEL 10 -Tr remains selected and in the conduction state during a period in which the control signal SEL 10  is at the H level. In this way, the source follower transistor SF 10 -Tr outputs, to the vertical signal line LSGN 10 , a read-out signal VSL (PIXOUT) of a column output, which is obtained by converting the charges of the floating diffusion FD 10  with a gain into a voltage signal. These operations are performed simultaneously and in parallel for pixels in each row since, for example, the gates of the transfer transistors TG 10 -Tr, the reset transistors RST 10 -Tr, and the selection transistors SEL 10 -Tr in each row are connected to each other. 
     The vertical scanning circuit  30  drives the pixels in shutter and read-out rows through the row-scanning control lines under the control of the timing control circuit  60 . Further, the vertical scanning circuit  30  outputs, according to address signals, row selection signals indicating row addresses of the read-out rows from which signals are to be read out and the shutter rows in which the charges accumulated in the photodiodes PD are reset. 
     As described above, in a normal pixel reading operation, the vertical scanning circuit  30  drives the pixels in such a manner that shutter scan is followed by reading scan. 
     The reading circuit  40  includes a plurality of column signal processing circuits (not shown) arranged corresponding to the column outputs of the pixel part  20 , and the reading circuit  40  may be configured such that the plurality of column signal processing circuits can perform column parallel processing. 
     The reading circuit  40  may include a correlated double sampling (CDS) circuit, an analog-to-digital converter (ADC), an amplifier (AMP), a sample-and-hold (S/H) circuit, and the like. 
     As mentioned above, as shown in  FIG.  8 A , for example, the reading circuit  40  may include ADCs  41  for converting the read-out signals VSL output from the respective columns of the pixel part  20  into digital signals. Alternatively, as shown in  FIG.  8 B , for example, the reading circuit  40  may include amplifiers (AMPs)  42  for amplifying the read-out signals VSL output from the respective columns of the pixel part  20 . As yet another alternative, as shown in  FIG.  8 C , for example, the reading circuit  40  may include sample-and-hold (S/H) circuits  43  for sampling/holding the read-out signals VSL output from the respective columns of the pixel part  20 . 
     The horizontal scanning circuit  50  scans the signals processed in the plurality of column signal processing circuits of the reading circuit  40  such as ADCs, transfers the signals in a horizontal direction, and outputs the signals to a signal processing circuit (not shown). 
     The timing control circuit  60  generates timing signals required for signal processing in the pixel part  20 , the vertical scanning circuit  30 , the reading circuit  40 , the horizontal scanning circuit  50 , and the like. 
     The above description has described the configurations and functions of the parts of the solid-state imaging device  10  relating to the first embodiment. The following now describes, as an example, the specific configuration of the pinned photodiodes PPD serving as the photoelectric conversion parts relating to the first embodiment and how the pixels are arranged. 
     &lt;Specific Configuration of Pinned Photodiodes PDs&gt; 
     The following now describes, as an example, the specific configuration of the pinned photodiodes PD constituting the sharing pixel PXL 20  of the solid-state imaging device  10  relating to the first embodiment with reference to  FIG.  9   . 
       FIG.  9    is a simplified sectional view showing an example configuration of the main part of the sharing pixel PXL 20  of the solid-state imaging device relating to the first embodiment of the present invention, or a charge integrating and transferring system including the pinned photodiodes PD and transfer transistors. In the following, a reference number  200  indicates the pinned photodiode (PPD) portion. 
     The sharing pixel PXL 20  is formed in a substrate (in the present example, a first substrate  110 ) having a first substrate surface  1101  (for example, back surface) irradiated with light L and a second substrate surface  1102  that opposes the first substrate surface  1101  and defined by a separation layer SPL. The sharing pixel PXL 20  relating to the present embodiment shown in  FIG.  9    includes, for example, the first photodiode PD 10 , the first transfer transistor TG 10 -Tr, the floating diffusion FD 10 , and the separation layer SPL, and also includes a color filter part and a microlens, which are not shown. 
     Although a back-illuminated pixel is shown as an example in  FIG.  9   , the present invention may be applied to a front-illuminated pixel. 
     &lt;Configuration of Photodiode&gt; 
     The first photodiode PD 10  includes a semiconductor layer of a first conductivity type (in the present embodiment, the n type) (in the present embodiment, the n layer)  2102  that is buried in an epitaxial layer (p-epi)  2101  of a second conductivity type (in the present embodiment, the p-type) in the semiconductor substrate having the first substrate surface  1101  and the second substrate surface  1102  opposing the first substrate surface  1101 . The first photodiode PD 10  is capable of photoelectrically convert the received light and storing charges. On the respective lateral portions of the first photodiode PD 10  in the direction orthogonal to the normal to the substrate (the X direction), namely, on either side in the drawing, separation layers SPL (SPL 1 , SPL 2 ) of the second conductivity type (in the present embodiment, the p type) are formed with epitaxial layers (p-epi)  2101 R and  2101 L sandwiched therebetween. 
     In the first photodiode PD 10  shown in  FIG.  9   , the n layer (the first-conductivity-type semiconductor layer)  2102  has a p+ layer  2103  formed thereon on the second substrate surface  1102  side. A color filter part is formed on the light incidence surface of the epitaxial layer (p-epi)  2101 , and a microlens is further formed on the light incidence surface of the color filter part such that the microlens can appropriately concentrate the light on the first photodiode PD 10 . 
     &lt;Configuration of Separation Layer in X Direction (Column Direction)&gt; 
     An n+ layer  2105  serving as the floating diffusion FD 10  is formed on the p-type separation layer  2104  (SPL 1 ) on the second substrate surface  1102  side, which is arranged on the right side in the X direction (column direction) in  FIG.  9   . On the left side in the X direction (column direction) of  FIG.  9   , a p-type separation layer  2106  (SPL 2 ) is formed. A gate electrode  2107  of the first transfer transistor TG 0 -Tr is formed on the epitaxial layer (p-epi)  2101 R on the second substrate surface  1102  side with a gate insulator sandwiched therebetween. Under the first transfer transistor TG 10 -Tr, an overflow path OVP is formed extending from the first photodiode PD 10  to the floating diffusion FD 10 . The potential of the overflow path OVP can also be controlled through gate control, for example. 
     The sharing pixel PXL 20  relating to the first embodiment includes four PDs, one FD and other elements arranged characteristically in the following manner, to not only reduce the size of the pixels while the sensitivity and full well capacity remain unchanged but also prevent an increase in junction capacitance and wiring capacitance and prevent an increase in the capacitance of the floating diffusion FD 10  serving as an output node to prevent a drop in conversion gain and eventually achieve improved noise characteristics. 
     (Example Arrangement of Four PDs and One FD in Sharing Pixel PXL 20 ) 
     The following describes, as an example, how the four photodiodes PD 10 , PD 11 , PD 12  and PD 13 , the four transfer transistors TG 10 -Tr, TG 11 -Tr, TG 12 -Tr and TG 13 -Tr, one floating diffusion FD 10 , one reset transistor RST 10 -Tr, one source follower transistor SF 10 -Tr, and one selection transistor SEL 10 -Tr are arranged in the sharing pixel PXL 20 . The relative positions of the elements represented by the terms such as left and right in the following description can be only example and modified in any other manners than the illustrated example. 
       FIG.  10    is a simplified plan view showing, as an example, how the four photodiodes, four transfer transistors, one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are arranged in the sharing pixel relating to the first embodiment. 
     The sharing pixel PXL 20  has a rectangular region RCT 20  where the elements are formed. The rectangular region RCT 20  can be divided into a central region CTAR 20  positioned in the center, and a first region FSAR 20  and a second region SCAR 20  sandwiching the central region CTAR 20  therebetween (in the Y direction). 
     In the central region CTAR 20 , the floating diffusion FD 10  is arranged in the X- and Y-direction-wise central portion thereof, the reset transistor RST 10 -Tr is arranged on the right side of the floating diffusion FD 10  in the X direction, and the source follower transistor SF 10 -Tr and the selection transistor SEL 10 -Tr are arranged on the left side of the floating diffusion FD 10  in the X direction. 
     The first photodiode PD 10 , the first transfer transistor TG 10 -Tr, the third photodiode PD 12  and the third transfer transistor TG 12 -Tr are adjacent to each other in the X direction in the first region FSAR 20 . In the example shown in  FIG.  10   , the first photodiode PD 10  and the first transfer transistor TG 10 -Tr are formed in the left part (left half) of the first region FSAR 20 , and the third photodiode PD 12  and the third transfer transistor TG 12 -Tr are formed in the right part (right half) of the first region FSAR 20 . The first and third transfer transistors TG 10 -Tr and TG 12 -Tr are shaped like a triangle when seen from above, and formed near the central region CTAR 20  such that they are connected to the floating diffusion FD 10 . 
     The second photodiode PD 11 , the second transfer transistor TG 11 -Tr, the fourth photodiode PD 13  and the fourth transfer transistor TG 13 -Tr are adjacent to each other in the X direction in the second region SCAR 20 . In the example shown in  FIG.  10   , the second photodiode PD 11  and the second transfer transistor TG 11 -Tr are formed in the left part (left half) of the first region FSAR 2 , and the fourth photodiode PD 13  and the fourth transfer transistor TG 13 -Tr are formed in the right part (right half) of the first region FSAR 20 . The second and fourth transfer transistors TG 11 -Tr and TG 13 -Tr are shaped like a triangle when seen from above, and formed near the central region CTAR 20  such that they are connected to the floating diffusion FD 10 . 
     In the sharing pixel PXL 20  relating to the first embodiment, the floating diffusion FD 10  has a diffusion layer, the core part FBS of which is shaped like a rectangle that has the first lateral part SDP 1  and the second lateral part SDP 2 , which are opposite to each other, when seen from above. The core part FBS has a branch part FBR extending from the middle part of the second lateral part SDP 2  in the X direction (to the right). The branch part FBR is formed to allow the reset transistor RST 10 -Tr to be formed. In other words, the floating diffusion FD 10  is substantially T-shaped. In the central part CTR of the element formation area, the source follower transistor SF 10 -Tr is adjacent to the first lateral part SDP 1  of the floating diffusion FD 10  in the first direction (for example, the X direction) orthogonal to the first lateral part SDP 1 , and the reset transistor RST 10 -Tr is adjacent to the second lateral part SDP 2  of the floating diffusion FD 10  in the first direction. The floating diffusion FD 10  and the source follower transistor SF 10 -Tr are connected together via a wiring WR 20 . The selection transistor SEL 10 -Tr is adjacent to the source follower transistor SF 10 -Tr, to be specific, on the left side in the X direction. 
     Some of the photodiodes are adjacent to each other in the second direction (e.g., in the Y direction). To be specific, the first photodiode PD 10  and the second photodiode PD 11 , and the third photodiode PD 12  and the fourth photodiode PD 13 , are spaced away from each other with the first spacing D 1  therebetween that allows at least the source follower transistor SF 10 -Tr, the selection transistor SEL 10 -Tr, and the reset transistor T 10 -Tr (MOS transistor) to be formed. Some of the photoelectric conversion elements are adjacent to each other in the first direction (in the X direction). To be specific, the first photodiode PD 10  and the third photodiode PD 12 , and the second photodiode PD 11  and the fourth photodiode PD 13  are arranged with the second spacing D 2 , which is less than the first spacing D 1  (D 1 &gt;D 2 ). 
     The first transfer transistor TG 10 -Tr is arranged (formed) to connect the first-lateral-part edge SDT 11  (the upper left edge of the FD 10  in  FIG.  10   ), at which the first lateral part SDP 1  of the floating diffusion FD 10  terminates in the second direction (the Y direction), and the first edge (the lower right edge of the PD 10  in  FIG.  10   ) ED 111  of the first photodiode PD 10  that faces the first-lateral-part edge SDT 11 . Stated differently, the first transfer transistor TG 10 -Tr extends to bridge the first-lateral-part edge SDT 11  of the floating diffusion FD 10  and the first edge ED 111  of the corresponding photodiode PD 10 . 
     The second transfer transistor TG 11 -Tr is arranged (formed) to connect the first-lateral-part edge SDT 12  (the lower left edge of the FD 10  in  FIG.  10   ), at which the first lateral part SDP 1  of the floating diffusion FD 10  terminates in the second direction (the Y direction), and the first edge (the upper right edge of the PD 11  in  FIG.  10   ) ED 112  of the second photodiode PD 11  that faces the first-lateral-part edge SDT 12 . Stated differently, the second transfer transistor TG 11 -Tr extends to bridge the first-lateral-part edge SDT 12  of the floating diffusion FD 10  and the first edge ED 112  of the corresponding photodiode PD 10 . 
     The third transfer transistor TG 12 -Tr is arranged (formed) to connect the second-lateral-part edge SDT 21  (the upper right edge of the FD 10  in  FIG.  10   ), at which the second lateral part SDP 2  of the floating diffusion FD 10  terminates in the second direction (the Y direction), and the first edge (the lower left edge of the PD 12  in  FIG.  10   ) ED 121  of the third photodiode PD 12  that faces the second-lateral-part edge SDT 12 . Stated differently, the third transfer transistor TG 12 -Tr extends to bridge the second-lateral-part edge SDT 21  of the floating diffusion FD 10  and the edge ED 121  of the corresponding photodiode PD 10 . 
     The fourth transfer transistor TG 13 -Tr is arranged (formed) to connect the second-lateral-part edge SDT 22  (the lower right edge of the FD 10  in  FIG.  10   ), at which the second lateral part SDP 2  of the floating diffusion FD 10  terminates in the second direction (the Y direction), and the first edge (the upper left edge of the PD 13  in  FIG.  10   ) ED 122  of the fourth photodiode PD 13  that faces the second-lateral-part edge SDT 22 . Stated differently, the fourth transfer transistor TG 13 -Tr extends to bridge the second-lateral-part edge SDT 22  of the floating diffusion FD 10  and the edge ED 122  of the corresponding photodiode PD 10 . 
       FIG.  11    is a simplified sectional view showing the main part of the sharing pixel relating to the first embodiment and used to illustrate additional capacitance components added to the capacitance of the floating diffusion.  FIG.  12    is a simplified sectional view showing the main part of a sharing pixel of a comparative example that does not have the characteristic features of the sharing pixel relating to the first embodiment shown in  FIG.  11   , and used to illustrate additional capacitance components added to the capacitance of the floating diffusion. 
     As described above, in the first embodiment, in the central part CTR of the element formation area or between the photodiodes PD 10  and PD 11  and between the photodiodes PD 12  and PD 13 , which are adjacent to each other in the Y direction, the source follower transistor SF 10 -Tr is adjacent to the first lateral part SDP 1  of the floating diffusion FD 10  in the first direction (for example, the X direction) orthogonal to the first lateral part SDP 1 , and the reset transistor RST 10 -Tr is adjacent to the second lateral part SDP 2  of the floating diffusion FD 10  in the first direction. The selection transistor SEL 10 -Tr is adjacent to the source follower transistor SF 10 -Tr, to be specific, on the left side in the X direction. As shown in  FIG.  11   , the floating diffusion FD 10  and the source follower transistor SF 10 -Tr are connected together via the wiring WR 20 . 
     With the above-described configuration, the first embodiment can allow the wiring WR 20 , which is provided to connect the floating diffusion FD 10  and the gate of the source follower transistor SF 10 -Tr, to be significantly shorter than in the comparative example shown in  FIG.  12   . In other words, in the comparative example shown in  FIG.  12   , the wiring length LMC of the wiring WR 20   c , which is connected to the floating diffusion FD 10 , extending from the source follower transistor SF 10 -Tr and the reset transistor RST-Tr is significantly greater than the wiring length LPE achieved by the arrangement relating to the present embodiment shown in  FIG.  11   . For this reason, the comparative example has such disadvantageous as an increase in the junction capacitance and the wiring capacitance for electrical connection, which disadvantageously increases the capacitance (Cfd) of the FD node, reduces the conversion gain and causes the noise characteristics to drop. In the comparative example shown in  FIG.  12   , the additional capacitance components include the junction capacitance C 1  in the n+ diffusion layer  2015  forming the floating diffusion FD, the inter-wiring capacitance C 2  between the wiring WR 20   c  and the photodiode PD, the inter-wiring capacitance C 3  between the wiring WR 20   c  and the separation layer ST 1 , the gate capacitance C 4  of the source follower transistor SF-Tr, and the junction capacitance C 5  in the n+ diffusion layer of the reset transistor RST-Tr. 
     According to the arrangement relating to the first embodiment, on the other hand, the wiring length LPE of the wiring WR 20 , which is connected to the floating diffusion FD 10 , extending from the source follower transistor SF 10 -Tr and the reset transistor RST-Tr is significantly less than the wiring length LMC in the comparative example shown in  FIG.  12   . This means that the present example can advantageously reduce the junction capacitance and the wiring capacitance for electrical connection, which can reduce the capacitance (Cfd) of the FD node, increase the conversion gain and achieve improved noise characteristics. According to the arrangement relating to the present embodiment shown in  FIG.  11   , the additional capacitance components include the junction capacitance C 11  in the n+ diffusion layer  2015  forming the floating diffusion FD, the inter-wiring capacitance C 12  between the wiring WR 20  and the separation layer ST 1 , and the gate capacitance C 13  of the source follower transistor SF 10 -Tr. 
     In the first embodiment, the photodiodes are arranged around the floating diffusion FD 10  to form a square (i.e., arranged radially). The first and second photodiodes PD 10  and PD 11 , and the third and fourth photodiodes PD 12  and PD 13 , which are adjacent to each other in the second direction (e.g., in the Y direction), are spaced away from each other with the first spacing D 1  therebetween that allows at least the source follower transistor SF 10 -Tr, the selection transistor SEL 10 -Tr, and the reset transistor T 10 -Tr (MOS transistor) to be formed. The first and third photodiodes PD 10  and PD 12 , and the second and fourth photodiodes PD 11  and PD 13 , which are adjacent to each other in the first direction (in the X direction) are spaced away from each other with the second spacing D 2 , which is less than the first spacing D 1  (D 1 &gt;D 2 ). 
     Having the above-described configuration, the first embodiment can allow the core part FBS of the floating diffusion FD 10  to be shaped like a narrow rectangle, thereby allowing the floating diffusion FD 10  to have as small area as possible. This can advantageously result in reducing the capacitance of the floating diffusion FD 10  reliably, increasing the conversion gain, and significantly reducing the noise. In addition, since the floating diffusion FD 10  has a reduced area, the size of the pixels can be reliably reduced. 
     The following now simulates and compares, in terms of the capacitance of the floating diffusion FD, the wiring capacitance, their total capacitance, and the size of the pixels, the layout of the solid-state imaging device  10  shown in  FIG.  10    relating to the first embodiment of the present invention, a first comparative example or the layout shown in  FIG.  4   , and a second comparative example or the layout shown in  FIG.  5   . 
       FIGS.  13 A to  13 C  respectively show the layout of the solid-state imaging device relating to the first embodiment of the present invention, the layout of the first comparative example, and the layout of the second comparative example, which are compared against each other in terms of the FD node capacitance, wiring capacitance, their total capacitance, and size of the pixels.  FIG.  14    is a table showing the FD node capacitance, wiring capacitance, their total capacitance, and size of the pixels observed when the layout of the solid-state imaging device relating to the first embodiment of the present invention, the layout of the first comparative example and the layout of the second comparative example are applied. In  FIGS.  13 A to  13 C , the reference sign FD W indicates the junction area of the floating diffusion FD, and the letter “W” represents the inlet width of the transfer transistor TG 0 , TG 10 . In  FIG.  14   , the FD node capacitance NCAP, the wiring capacitance WCAP, and the total capacitance TCAP are expressed in relative ratios with the capacitance accomplished by the present invention being expressed as 1. 
     The simulations reveal that the node capacitance NCP of the floating diffusion FD is 0.5, the wiring capacitance WCAP is 0.5 and the total capacitance TCAP is 1 when the layout of the present invention is adopted. The size of the pixels PSZ is 1.5 μm. When the first comparative example is employed, the node capacitance NCP of the floating diffusion FD is 1, the wiring capacitance WCAP is 0.5 and the total capacitance TCAP is 1.5. The size of the pixels PSZ is 2 μm. When the second comparative example is employed, the node capacitance NCP of the floating diffusion FD is 0.5, the wiring capacitance WCAP is 1 and the total capacitance TCAP is 1.5. The size of the pixels PSZ is 1.5 μm. 
     These results indicate that the solid-state imaging device relating to the first embodiment of the present invention can have a significantly smaller junction area FD W for the floating diffusion FD than the solid-state imaging devices relating to the first and second comparative examples, thereby achieving reduction in the FD node capacitance NCAP and the wiring capacitance WCAP. This means that the first embodiment can advantageously reduce the total capacitance TCAP reliably, increase the conversion gain, and improve the noise characteristics. In addition, since the floating diffusion FD 10  has a reduced area, the size of the pixels PSZ can be reliably reduced. 
     As described above, the first embodiment can allow four pixels to share their pixel components, so that the size of the photodiode PD per pixel can be maximized. This results in not only reducing the size of the pixels while the sensitivity and full well capacity remain unchanged but also simplifying the layout, significantly reducing the wiring WR 20  for connecting the floating diffusion FD 10  and the gate of the source follower transistor SF 10 -Tr and achieving a sufficiently reduced size for the floating diffusion FD 10 , so that the floating diffusion FD 10  can keep high conversion gain. In other words, the first embodiment can not only reduce the size of the pixels while the sensitivity and full well capacity remain unchanged but also prevent an increase in junction capacitance and wiring capacitance and prevent an increase in the capacitance of the floating diffusion FD 10  serving as an output node, to prevent a drop in conversion gain and eventually achieve improved noise characteristics. 
     Second Embodiment 
       FIG.  15    is a circuit diagram showing an example of sharing pixels of a solid-state imaging device relating to a second embodiment of the present invention.  FIG.  16    is a simplified plan view showing, as an example, how four photodiodes, four transfer transistors, one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are arranged in a sharing pixel relating to the second embodiment. 
     A sharing pixel PXL 20 A of a solid-state imaging device  10 A relating to the second embodiment differs from the sharing pixel PXL 20  of the solid-state imaging device  10  relating to the above-described first embodiment in the following points. 
     The sharing pixel PXL 20 A of the solid-state imaging device  10 A of the second embodiment includes shutter gate transistors SG 10 -Tr, SG 11 -Tr, SG 12 -Tr and SG 13 -Tr, which are connected between (i) the charge storage parts PND 10 , PND 11 , PND 12 , PND 13  of the photodiodes PD 10 , PD 11 , PD 12  and PD 13  and (ii) the power supply line Vaapix of the power supply voltage VAAPIX and which are configured to serve as charge overflow gate elements for allowing the charges to overflow from the photodiodes PD 10 , PD 11 , PD 12  and PD 13  toward the floating diffusion region or a region other than the floating diffusion region. The shutter gate transistors SG 10 -Tr, SG 11 -Tr, SG  12 -Tr and SG 13 -Tr serving as charge overflow gate elements are arranged such that they are connected to second edges ED 211 , ED 212 , ED 221  and EED 222  of the photodiodes PD 10 , PD 11 , PD 12  and PD 1 . The second edges ED 211 , ED 212 , ED 221  and ED 222  are closer to an outer edge and separated away from the first edges ED 111 , ED 112 , ED 121  and ED 122  on which the transfer transistors TG 10 -Tr, TG 11 -Tr, TG 2 -Tr and TG 13 -Tr are arranged. 
     Specifically, the first transfer transistor TG 10 -Tr, which serves as a first transfer element, is connected between the first photodiode PD 10  and the floating diffusion FD 10 , and the first shutter gate transistor SG 10 -Tr, which serves as the first charge overflow gate element, is connected between the first photodiode PD 10  and the predetermined fixed potential VAAPIX. The first shutter gate transistor SG 10 -Tr is arranged such that it is connected to the second edge ED 211  of the first photodiode PD 10 , which is closer to an outer edge and separated away from the first edge ED 111  on which the first transfer transistor TG 10 -Tr is arranged, as shown in  FIG.  16   . 
     The second transfer transistor TG 11 -Tr, which serves as the second transfer element, is connected between the second photodiode PD 11  and the floating diffusion FD 10 , and the second shutter gate transistor SG 11 -Tr, which serves as a second charge overflow gate element, is connected between the second photodiode PD 11  and the predetermined fixed potential VAAPIX. The second shutter gate transistor SG 11 -Tr is arranged such that it is connected to the second edge ED 212  of the second photodiode PD 11 , which is closer to an outer edge and separated away from the first edge ED 112  on which the second transfer transistor TG 11 -Tr is arranged, as shown in  FIG.  16   . 
     The third transfer transistor TG 12 -Tr, which serves as the third transfer element, is connected between the third photodiode PD 12  and the floating diffusion FD 10 , and the third shutter gate transistor SG 12 -Tr, which serves as a third charge overflow gate element, is connected between the third photodiode PD 12  and the predetermined fixed potential VAAPIX. The third shutter gate transistor SG 12 -Tr is arranged such that it is connected to the second edge ED 221  of the third photodiode PD 12 , which is closer to an outer edge and separated away from the first edge ED 121  on which the third transfer transistor TG 12 -Tr is arranged, as shown in  FIG.  16   . 
     The fourth transfer transistor TG 13 -Tr, which serves as the fourth transfer element, is connected between the fourth photodiode PD 13  and the floating diffusion FD 10 , and the fourth shutter gate transistor SG 13 -Tr, which serves as a fourth charge overflow gate element, is connected between the fourth photodiode PD 13  and the predetermined fixed potential VAAPIX. The fourth shutter gate transistor SG 13 -Tr is arranged such that it is connected to the second edge ED 222  of the fourth photodiode PD 13 , which is closer to an outer edge and separated away from the first edge ED 122  on which the fourth transfer transistor TG 13 -Tr is arranged, as shown in  FIG.  16   . 
     As described above, the first shutter gate transistor SG 10 -Tr serving as the first charge overflow gate element is connected between the first photodiode PD 10  and the predetermined fixed potential VAAPIX and controlled by a control signal SG 10  applied thereto through a control line. The first shutter gate transistor SG 10 -Tr remains selected and in the conduction state during the period in which the control signal SG 10  is at the H level, to form a blooming path to release the charges generated at the first photodiode PD 10  (to form an antiblooming path for the floating diffusion FD) between the first photodiode PD 10  and the predetermined fixed potential VAAPIX. In this way, unnecessary charges are released to the fixed potential VAAPIX. 
     As described above, the first transfer transistor TG 10 -Tr and the first shutter gate transistor SG 10 -Tr are driven and controlled at individually selected timings. 
     The first transfer transistor TG 10 -Tr is connected between the first photodiode PD 1  and the floating diffusion FD 10  and controlled by a control signal TG 10  applied to the gate thereof through a control line. The first transfer transistor TG 10 -Tr remains selected and in the conduction state during a transfer period PT in which the control signal TG 10  is at the high (H) level, to transfer to the floating diffusion FD 10  the charges (electrons) produced by the photoelectric conversion and then stored in the first photodiode PD 10 . After the first photodiode PD 10  and the floating diffusion FD 10  are reset to a predetermined reset potential, the first transfer transistor TG 10 -Tr enters the non-conduction state with the control signal TG 10  being set to the low (L) level and the first photodiode PD 10  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the fixed potential VAAPIX as overflow charges through the overflow path under the first shutter gate transistor SG 10 -Tr. 
     The second shutter gate transistor SG 11 -Tr serving as the second charge overflow gate element is connected between the second photodiode PD 11  and the predetermined fixed potential VAAPIX and controlled by a control signal SG 11  applied thereto through a control line. The second shutter gate transistor SG 11 -Tr remains selected and in the conduction state during the period in which the control signal SG 11  is at the H level, to form a blooming path to release the charges generated at the second photodiode PD 11  (to form an antiblooming path for the floating diffusion FD) between the second photodiode PD 11  and the predetermined fixed potential VAAPIX. In this way, unnecessary charges are released to the fixed potential VAAPIX. 
     As described above, the second transfer transistor TG 11 -Tr and the second shutter gate transistor SG 11 -Tr are driven and controlled at individually selected timings. After the second photodiode PD 11  and the floating diffusion FD 10  are reset to a predetermined reset potential, the second transfer transistor TG 11 -Tr enters the non-conduction state with the control signal TG 11  being set to the low (L) level and the second photodiode PD 11  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the fixed potential VAAPIX as overflow charges through the overflow path under the second shutter gate transistor SG 11 -Tr. 
     The third shutter gate transistor SG 12 -Tr serving as the third charge overflow gate element is connected between the third photodiode PD 12  and the predetermined fixed potential VAAPIX and controlled by a control signal SG 12  applied thereto through a control line. The third shutter gate transistor SG 12 -Tr remains selected and in the conduction state during the period in which the control signal SG 12  is at the H level, to form a blooming path to release the charges generated at the third photodiode PD 12  (to form an antiblooming path for the floating diffusion FD) between the third photodiode PD 12  and the predetermined fixed potential VAAPIX. In this way, unnecessary charges are released to the fixed potential VAAPIX. 
     As described above, the third transfer transistor TG 12 -Tr and the third shutter gate transistor SG 12 -Tr are driven and controlled at individually selected timings. After the third photodiode PD 12  and the floating diffusion FD 10  are reset to a predetermined reset potential, the third transfer transistor TG 12 -Tr enters the non-conduction state with the control signal TG 12  being set to the low (L) level and the third photodiode PD 12  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the fixed potential VAAPIX as overflow charges through the overflow path under the third shutter gate transistor SG 12 -Tr. 
     The fourth shutter gate transistor SG 13 -Tr serving as the fourth charge overflow gate element is connected between the fourth photodiode PD 13  and the predetermined fixed potential VAAPIX and controlled by a control signal SG 13  applied thereto through a control line. The fourth shutter gate transistor SG 13 -Tr remains selected and in the conduction state during the period in which the control signal SG 13  is at the H level, to form a blooming path to release the charges generated at the fourth photodiode PD 13  (to form an antiblooming path for the floating diffusion FD) between the fourth photodiode PD 13  and the predetermined fixed potential VAAPIX. In this way, unnecessary charges are released to the fixed potential VAAPIX. 
     As described above, the fourth transfer transistor TG 13 -Tr and the fourth shutter gate transistor SG 13 -Tr are driven and controlled at individually selected timings. After the fourth photodiode PD 13  and the floating diffusion FD 10  are reset to a predetermined reset potential, the fourth transfer transistor TG 13 -Tr enters the non-conduction state with the control signal TG 13  being set to the low (L) level and the fourth photodiode PD 12  enters an integration period PI. Under these circumstances, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the fixed potential VAAPIX as overflow charges through the overflow path under the fourth shutter gate transistor SG 13 -Tr. 
     In addition, for the first shutter gate transistor SG 10 -Tr serving as the first charge overflow gate element, the second shutter gate transistor SG 11 -Tr serving as the second charge overflow element, the third shutter gate transistor SG 12 -Tr serving as the third charge overflow element, and the fourth shutter gate transistor SG 13 -Tr serving as the fourth charge overflow element, their threshold values may be individually adjusted. 
       FIG.  17    is a simplified sectional view showing an example configuration of the main part of a sharing pixel relating to the second embodiment of the present invention or a charge integrating and transferring system including the shutter gate transistors. 
     The configuration shown in  FIG.  17    differs from that shown in  FIG.  9    in that the former has the shutter gate transistors. 
     &lt;Configuration of Separation Layer in X Direction (Column Direction)&gt; 
     An n+ layer  2105  serving as the floating diffusion FD is formed on the p-type separation layer  2104  (SPL 1 ), which is arranged on the right side in the X direction (column direction) in  FIG.  17   , on the second substrate surface  1102  side. An n+ layer  2108  serving as the drain of the shutter gate transistor TSG 0 -Tr is formed on the p-type separation layer  2106  (SPL 2 ), which is arranged on the left side in the X direction (column direction) in  FIG.  17   , on the second substrate surface  1102  side. A gate electrode  2107  of the first transfer transistor TG 0 -Tr is formed on the epitaxial layer (p-epi)  2101 R on the second substrate surface  1102  side with a gate insulator sandwiched therebetween. Under the first transfer transistor TG 10 -Tr, an overflow path OVP is formed extending from the first photodiode PD 10  to the floating diffusion FD 10 . The potential of the overflow path OVP can also be controlled through gate control, for example. 
     A gate electrode  2109  of the first shutter gate transistor SG 10 -Tr is formed on the epitaxial layer (p-epi)  2101 L on the second substrate surface  1102  side with a gate insulator sandwiched therebetween. Under the first shutter gate transistor SG 10 -Tr, a blooming path EFP (an antiblooming path for the floating diffusion FD) is formed to extend between the photodiode PD 10  and the n+ layer  2108  to release the charges generated at the first photodiode PD 10 . 
     With the above-described structure, if the intensity of the incident light is very high (the amount of the incident light is very large), the charges above the full well capacity overflow into the floating diffusion FD as overflow charges through the overflow path OVP under the first transfer transistor TG 10 -Tr. 
     Irregular and intense light may enter the first photodiode PD 10  while comparing is performed, e.g., while the AD conversion is performed. If such is the case, charges may overflow from the photodiode PD 10  to the floating diffusion FD 10  and the level of the floating diffusion FD 10  serving as the output node may change. As a consequence, the AD conversion may possibly fail to be completed successfully. To address this issue, the present embodiment employs the first shutter gate transistor SG 10 -Tr. In this way, if irregular and intense light enters the first photodiode PD 10  during comparing, unnecessary charges may be released from the first photodiode PD 10  to a region outside the floating diffusion FD 10  region. The first shutter gate transistor SG 10 -Tr thus prevents a change in the level of the floating diffusion FD 10 , which may be caused by the charges overflowing from the first photodiode PD 10  to the floating diffusion FD 10 . In this way, the pixel is configured to be capable of successfully completing AD conversion by preventing a change in the FD level, which may be caused if irregular and intense light enters the first photodiode PD 10  while comparing is performed, e.g., while the AD conversion is performed. The same applies to the other photodiodes PD 11 , PD 12  and PD 13 . 
     As described above, the second embodiment includes the shutter gate transistors SG 10 -Tr, SG 11 -Tr, SG 12 -Tr and SG 13 -Tr, which are connected between (i) the charge storage parts of the photodiodes PD 10 , PD 11 , PD 12  and PD 13  and (ii) the power supply line Vaapix of the power supply voltage VAAPIX and which are configured to serve as charge overflow gate elements for allowing the charges to overflow from the photodiodes PD toward the floating diffusion region or a region other than the floating diffusion region. The second embodiment thus can not only produce the same effects as the above-described first embodiment but also produce the following effects. 
     The second embodiment can prevent mixing of charges (which can result in false signals), which is caused by the signals indicative of the charges exceeding the charges that can be stored on a given photodiode PD (overflow charges) flowing into adjacent pixels. 
     Third Embodiment 
       FIG.  18    is a circuit diagram showing an example of sharing pixels of a solid-state imaging device relating to a third embodiment of the present invention.  FIG.  19    is a simplified plan view showing, as an example, how four photodiodes, four transfer transistors, one floating diffusion FD, one reset transistor, one source follower transistor and one selection transistor are arranged in the sharing pixel relating to the third embodiment. 
     A sharing pixel PXL 20 B of a solid-state imaging device  10 B relating to the third embodiment implements a dual-gain scheme, which is configured in a less complicated manner since the solid-state imaging devices  10  and  10 A relating to the first and second embodiments can achieve a reduced capacitance in the floating diffusion FD 10 . The sharing pixel  20 B of the solid-state imaging device  10 B relating to the third embodiment differs from the sharing pixel  20 A of the solid-state imaging device  10 A relating to the above-described second embodiment in the following points. 
     The sharing pixel PXL 20 B relating to the third embodiment has a gain switching part  210  for switching the conversion gain of the source follower transistor SF 10 -Tr serving as the output buffer part. The gain switching part  210  is configured to change the amount of charges in the floating diffusion FD 10  serving as the output node between a first capacitance and a second capacitance, so that the conversion gain of the source follower transistor SF 10 -Tr serving as the output buffer part can be changed between a first conversion gain corresponding to the first capacitance (for example, high conversion gain: HCG) and a second conversion gain corresponding to the second capacitance (for example, low conversion gain: LCG). The third embodiment employs a dual read-out scheme, and one of the first and second conversion gains is selected by the amount of charges to be read and the selected conversion gain is used. 
     The gain switching part  210  includes a storage transistor BIN 10 -Tr serving as a storage element connected to the floating diffusion FD 10 , and a storage capacitor CS 1  serving as a storage capacitance element configured to store the charges on the floating diffusion FD 10  via the storage transistor BIN 10 -Tr. 
     The storage transistor BIN 10 -Tr is connected between the floating diffusion FD 10  and the reset transistor RST 10 -Tr, and the storage capacitor C 5  is connected between (i) a connection node ND 12  between the reset transistor RST 10 -Tr and the storage transistor BIN 10 -Tr and (ii) the reference potential VSS. The storage transistor BIN 10 -Tr is controlled by a control signal BIN 10  applied to the gate thereof through a control line. The storage transistor BIN 10 -Tr remains selected and in the conduction state during a reset period in which the control signal BIN 10  is at the H level, to connect the floating diffusion FD 10  and the storage capacitor CS 1 . 
     In the third embodiment, the storage transistor BIN 10 -Tr is arranged in the central region CTAR 20  of the element formation region between the floating diffusion FD 10  and the reset transistor RST 10 -Tr, as shown in  FIG.  19   . 
     In the third embodiment, a read-out operation with a changeable gain is performed in the following manner. A first-conversion-gain signal read-out operation HCGSRD is performed while the storage transistor BIN 10 -Tr remains in the non-conduction state, so that the charges in the floating diffusion FD 10  serving as the output node ND 10  are separated from the charges in the storage capacitor CS. A first-conversion-gain reset read-out operation HCGRRD is performed while the storage transistor BIN 10 -Tr remains in the non-conduction state, so that the charges in the floating diffusion FD 10  serving as the output node ND 10  are separated from the charges in the storage capacitor CS. A second-conversion-gain signal read-out operation LCGSRD is performed while the storage transistor BIN 10 -Tr remains in the conduction state, so that the charges in the floating diffusion FD 10  serving as the output node ND 10  are mixed with the charges in the storage capacitor CS. A second-conversion-gain reset read-out operation LCGRRD is performed while the reset transistor RST 120 -Tr and the storage transistor BIN 10 -Tr remain in the conduction state, so that the charges in the floating diffusion FD 10  serving as the output node ND 10  and the charges in the storage capacitor CS are cleared. 
     As described above, the third embodiment includes the gain switching part  210 , which includes the storage transistor BIN 10 -Tr and the storage capacitor CS. The gain switching part  210  is configured to change the amount of charges in the floating diffusion FD 10  serving as the output node between the first capacitance and the second capacitance, so that the conversion gain of the source follower transistor SF 10 -Tr serving as the output buffer part can be changed between the first conversion gain corresponding to the first capacitance (for example, high conversion gain: HCG) and the second conversion gain corresponding to the second capacitance (for example, low conversion gain: LCG). With such configurations, the full well capacity (FWC) is small when the conversion gain is set at the high conversion gain (HCG) and large when the conversion gain is set at the low conversion gain (LCG). 
     The following now describes, as an example, a sequence of operations performed to read signals from the sharing pixel in the solid-state-imaging device relating to the third embodiment. 
       FIG.  20    is a timing chart including parts (A) to (J) to illustrate an example sequence of operations performed in a read-out mode on sharing pixels in the solid-state imaging device relating to the third embodiment of the present invention. 
     In  FIG.  20   , the part (A) presents the control signal TG 10  for the first transfer transistor TG 10 -Tr, which is to be accessed in the read-out mode, the part (B) presents the control signal SG 10  for the first shutter gate transistor SG 10 -Tr, the part (C) presents the control signal TG 11  for the second transfer transistor TG 11 -Tr, which is to be accessed in the read-out mode, the part (D) presents the control signal SG 11  for the second shutter gate transistor SG 11 -Tr, the part (E) presents the control signal TG 12  for the third transfer transistor TG 12 -Tr, which is to be accessed in the read-out mode, the part (F) presents the control signal SG 12  for the third shutter gate transistor SG 12 -Tr, the part (G) presents the control signal TG 13  of the fourth transistor TG 13 -Tr, which is to be accessed in the read-out mode, the part (H) presents the control signal SG 13  for the fourth shutter gate transistor SG 13 -Tr, the part (I) shows the control signal BIN 10  for the storage transistor BIN 10 -Tr, and the part (J) shows the control signal RST 10  for the reset transistor RST 10 -Tr. 
     In the read-out mode RMD, the control signals TG 10 , TG 11 , TG 12  and TG 13  are set at the low level so that the transfer transistors TG 10 -Tr, TG 11 -Tr, TG 12 -Tr and TG 13 -Tr remain in the non-conduction state, and the level of the control signals SG 10 , SG 11 , SG 12  and SG 13  is switched from the high level to the low level so that the state of the shutter gate transistors SG 10 -Tr, SG 11 -Tr, SG 12 -Tr and SG 13 -TR is switched from the conduction state to the non-conduction state. At the timing when the state of the shutter gate transistors SG 10 -Tr, SG 11 -Tr, SG 12 -Tr and SG 13 -Tr is switched from the conduction state to the non-conduction state, an exposure period starts. Additionally, the level of the control signal RST 10  remains at the high level for a predetermined period of time, so that the reset transistor RST 10 -Tr remains in the conduction state, and the level of the control signal BIN 10  remains at the high level for a predetermined period of time, so that the storage transistor BIN 10 -Tr remains in the conduction state. In this way, during a reset period RP, the floating diffusion FD 10  serving as the output node ND 10  remains in the reset state. 
     Under these circumstances, the charges stored in the first photodiode PD 10  are read. To do so, the control signals RST 10  and BIN 10  are set at the high level, so that the floating diffusion FD 10  serving as the output node ND 10  is reset. The control signal BIN 10  remains at the high level for a predetermined period of time, so that the storage transistor BIN 10 -Tr remains in the conduction state and the charges at the floating diffusion FD 10  serving as the output node ND 10  are combined with the charges at the storage capacitor CS serving as the storage capacitance element. Consequently, the amount of the charges at the floating diffusion FD 10  is maintained at the second capacitance. This allows the second-conversion-gain reset read-out operation LCGRRD to be performed. Under these circumstances, in a reset read-out period PRRD following the reset period PR, the second-conversion-gain reset read-out operation LCGRRD is performed to read a read-out reset signal LCGVRST resulting from conversion performed with the second conversion gain corresponding to the second capacitance in the floating diffusion FD 10  serving as the output node ND 10  from the source follower transistor SF 10 -Tr serving as the output buffer and to process the read-out reset signal LCGVRST. 
     Following this, the control signal BIN 10  is switched to the low level so that the storage transistor BIN 10 -Tr remains in the non-conduction state and the charges at the floating diffusion FD 10  serving as the output node ND 10  are separated from the charges at the storage capacitor CS serving as the storage capacitance element. Consequently, the amount of charges at the floating diffusion FD 10  is maintained at the first capacitance. This allows the first-conversion-gain reset read-out operation HCGRRD to be performed. Under these circumstances, in another reset read-out period PRRD following the reset period PR, the first-conversion-gain reset read-out operation HCGRRD is performed to read a read-out reset signal HCGVRST resulting from conversion performed with the first conversion gain (high conversion gain: HCG) corresponding to the first capacitance in the floating diffusion FD 10  serving as the output node ND 10  from the source follower transistor SF 10 -Tr serving as the output buffer and to process the read-out reset signal HCGVRST. 
     After the reset read-out period PPRD, the control signal TG 10  remains at the high level for a predetermined period of time, so that the charges stored in the photodiode PD 10  are transferred to the floating diffusion FD 10  in this first transfer period PT 1 . In a first read-out period PRD 1  following the first transfer period PT 1 , the first-conversion-gain read-out operation HCGSRD is performed to read, from the source follower transistor SF 10 -Tr serving as the output buffer, a read-out signal HCGVSIG resulting from conversion performed with the first conversion gain corresponding to the first capacitance of the floating diffusion FD 10  serving as the output node ND 10  and process the read-out signal HCGVSIG. 
     After the first read-out period PRD 1 , the control signal BIN 10  is switched to the high level, so that the storage transistor BIN 10 -Tr remains in the conduction state and the charges at the floating diffusion FD 10  serving as the output node ND 10  are combined with the charges at the storage capacitor CS serving as the storage capacitance element. Consequently, the amount of charges at the floating diffusion FD 10  is maintained at the second charge amount. This allows the second-conversion gain reset read-out operation LCGRRD to be performed. Under these circumstances, the control signal TG 0  is switched to the high level after the first read-out period PRD 1  and remains at the high level for a predetermined period of time, so that the charges stored in the photodiode PD 10  are transferred to the floating diffusion FD 10  in this second transfer period PT 2 . After the second transfer period PT 2 , the control signal SG 10  is switched to the high level so that the first shutter gate transistor SG 10 -Tr remains in the conduction state. In the subsequent second read-out period PRD 2 , the second-conversion-gain read-out operation LCGSRD is performed to read, from the source follower transistor SF 10 -Tr serving as the output buffer, a read-out signal LCGVSIG resulting from conversion performed with the second conversion gain corresponding to the second capacitance in the floating diffusion FD 10  serving as the output node ND 10  and process the read-out signal LCGVSIG. 
     Once the charges stored in the first photodiode PD 10  have been read in the above-described manner, the charges stored in the second photodiode PD 11  are subsequently read. To do so, while the control signal BIN 10  remains at the high level, the control signal RST 10  remains at the high level for a predetermined period of time, so that the reset transistor RST 10 -Tr remains in the conduction state. In this way, during a reset period RP, the floating diffusion FD 10  serving as the output node ND 10  remains in the reset state. After this, in the same manner as the charges stored in the first photodiode PD 10  are processed, the charges stored in the second, third and fourth photodiodes PD 11 , PD 12  and PD 13  are sequentially processed. Therefore, the processing is not described in detail here. 
     The third embodiment can provide for a widened dynamic range by performing reading in a predetermined mode while the pixel achieves a small size. Additionally, the third embodiment is capable of substantially achieving a widened dynamic range and a raised frame rate, achieving reduced noise, and maximizing the effective pixel region and value per cost. 
     Fourth Embodiment 
       FIG.  21    is a circuit diagram showing an example configuration of the sharing pixels of a solid-state imaging device  10 C relating to a fourth embodiment of the present invention. 
     In the solid-state imaging device  10 C relating to the fourth embodiment, a pixel part  20 C includes unit pixels PXLC, and each unit pixel PXLC includes a photoelectric conversion reading part  220  and a signal holding part  230 . The solid-state imaging device  10 C is configured, for example, as a stacked CMOS image sensor capable of operating in a global shutter mode and substantially achieving a widened dynamic range and an enhanced frame rate. 
     In the stacked structure, reading nodes ND 11  of the photoelectric conversion reading parts  220  of the pixel array in a first substrate  110  are electrically connected to input nodes ND 20  of the signal holding parts  230  of sharing pixels PXL 20 C in a second substrate  120  through via microbumps BMP (die-to-die vias) or the like as shown in  FIG.  21   , for example. 
     As will be described in detail below, in the solid-state imaging device  10 C relating to the fourth embodiment, in a voltage mode, a pixel signal is sampled into the signal holding part serving as a pixel signal storage, which takes place in all of the pixels at the same time and in parallel. The signal obtained by converting the read-out signal held in first to eighth signal holding capacitors is read out to a predetermined signal line, and the signal obtained by converting the read-out reset signal is read out to a predetermined signal line. The signals are read out to the respective signal lines simultaneously and in parallel, and fed to the column reading circuit  40 . 
     The following describes the configurations and functions of the pixel part  20 C of the solid-state imaging device  10 C. 
     Configuration of Unit Pixel PXLC and Pixel Part  20 C 
     The sharing pixels PXL 20 C arranged in the pixel part  20 C each include the photoelectric conversion reading part  220  and the signal holding part  230 , as shown in  FIG.  21   . The pixel part  20 C relating to the fourth embodiment is configured as a stacked CMOS image sensor made up by the first substrate  110  and the second substrate  120 . In the present example, as shown in  FIG.  21   , the photoelectric conversion reading part  220  is formed in the first substrate  110 , and the signal holding part  230  is formed in the second substrate  120 . 
     The photoelectric conversion reading part  220  includes a photodiode (a photoelectric conversion element) and an in-pixel amplifier. In the example shown in  FIG.  21   , the photoelectric conversion reading part  220  is based on a modification example of the sharing pixel PXL 20 B relating to the third embodiment shown in  FIG.  18   , for example. 
     Specifically, the photoelectric conversion reading part  220  differs from the sharing pixel PXL 20 B of  FIG.  18    in the following ways. In the photoelectric conversion reading part  220 , an output buffer part  221  includes the source follower transistor SF 10 -Tr, a current transistor IC 10 -Tr, and the reading node ND 11 . In other words, the photoelectric conversion reading part  220  includes the current transistor IC 10 -Tr, instead of the selection transistor SEL 10 -Tr of the sharing pixel PXL 20 B shown in  FIG.  18   . The drain and source of the current transistor IC 10 -Tr serving as a current source element are connected between the reading node ND 11  and the reference potential VSS (for example, GND). The gate of the current transistor IC 10 -Tr is connected to the feeding line of a control signal VBNPIX. A signal line LSGN 10  between the reading node ND 11  and the input part of the signal holding part  230  is driven by the current transistor IC 10 -Tr serving as the current source element. 
     In the photoelectric conversion reading part  220  relating to the fourth embodiment, the reading node ND 11  of the output buffer part  221  is connected to the input part of the signal holding part  230 . The photoelectric conversion reading part  220  is configured to convert the charges in the floating diffusion FD 10  serving as the output node ND 10  into a voltage signal at a level corresponding to the amount of charges and outputs the voltage signal VSL to the signal holding part  230 . 
     Furthermore, the photoelectric conversion reading part  220  outputs, in a transfer period PT following the integration period PI, a voltage signal VSL corresponding to the charges stored in the photodiodes PD 10 , PD 11 , PD 12  and PD 14  that are transferred to the floating diffusion FD 10  serving as the output node. The photoelectric conversion reading part  220  outputs a read-out reset signal (signal voltage) (VRST) and a read-out signal (signal voltage) (VSIG), as a pixel signal, to the signal holding part  230 . 
     The signal holding part  230  of the pixel  200 C basically includes an input part  231  including the input node ND 20 , a sample-and-hold part  232 , a first output part  233 , a second output part  234 , a third output part  235 , a fourth output part  236 , a fifth output part  237 , a sixth output part  238 , a seventh output part  239 , an eighth output part  240 , and holding nodes ND 21 , ND 22 , ND 23 , ND 24 , ND 25 , ND 26 , ND 27  and ND 28 . 
     The input part  231  is connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the signal line LSGN 10  and inputs, into the sample-and-hold part  232 , the read-out signal (VSIG 1 ) and the read-out reset signal (VRST 1 ) output from the reading node ND 11 . s 
     The sample-and-hold part  232  includes a first sampling transistor SHR 1 -Tr serving as a first switch element, a second sampling transistor SHS 1 -Tr serving as a second switch element, a third sampling transistor SHR 2 -Tr serving as a third switch element, a fourth sampling transistor SHS 2 -Tr serving as a fourth switch element, a fifth sampling transistor SHR 3 -Tr serving as a fifth switch element, a sixth sampling transistor SHS 3 -Tr serving as a sixth switch element, a fourth sampling transistor SHR 4 -Tr serving as a seventh switch element, and an eighth sampling transistor SHS 4 -Tr serving as an eighth switch element. The sample-and-hold part  232  further includes a first signal holding capacitor CR 21 , a second signal holding capacitor CS 21 , a third signal holding capacitor CR 22 , a fourth signal holding capacitor CS 22 , a fifth signal holding capacitor CR 23 , a sixth signal holding capacitor CS 23 , a seventh signal holding capacitor CR 24 , and an eighth signal holding capacitor CS 24 . 
     The first sampling transistor SHR 1 -Tr is connected between the holding node ND 21  and the input node ND 20  connected to the signal line LSGN 10 . The first sampling transistor SHR 1 -Tr keeps the first signal holding capacitor CR 21  of the sample-and-hold part  232  selectively connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the holding node ND 21  during a global shutter period or signal holding capacitor clear period. The first sampling transistor SHR 1 -Tr is in the conduction state during a period in which, for example, a control signal SHR 1  is at the high level. The first signal holding capacitor CR 21  is connected between the holding node ND 21  and the reference potential VSS. 
     The second sampling transistor SHS 1 -Tr is connected between the holding node ND 22  and the input node ND 20  connected to the signal line LSGN 10 . The second sampling transistor SHS 1 -Tr keeps the second signal holding capacitor CS 21  of the sample-and-hold part  232  selectively connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the holding node ND 22  during a global shutter period or signal holding capacitor clear period. The second sampling transistor SHS 1 -Tr is in the conduction state during a period in which, for example, a control signal SHS 1  is at the high level. The second signal holding capacitor CS 21  is connected between the holding node ND 22  and the reference potential VSS. 
     The third sampling transistor SHR 2  Tr is connected between the holding node ND 23  and the input node ND 20  connected to the signal line LSGN 10 . The third sampling transistor SHR 2 -Tr keeps the third signal holding capacitor CR 22  of the sample-and-hold part  232  selectively connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the holding node ND 23  during a global shutter period or signal holding capacitor clear period. The third sampling transistor SHR 2 -Tr is in the conduction state during a period in which, for example, a control signal SHR 2  is at the high level. The third signal holding capacitor CR 22  is connected between the holding node ND 23  and the reference potential VSS. 
     The fourth sampling transistor SHS 2  Tr is connected between the holding node ND 24  and the input node ND 20  connected to the signal line LSGN 10 . The fourth sampling transistor SHS 2 -Tr keeps the fourth signal holding capacitor CS 22  of the sample-and-hold part  232  selectively connected to the reading node ND 112  of the photoelectric conversion reading part  220  via the holding node ND 24  during a global shutter period or signal holding capacitor clear period. The fourth sampling transistor SHS 2 -Tr is in the conduction state during a period in which, for example, a control signal SHS 2  is at the high level. The fourth signal holding capacitor CS 22  is connected between the holding node ND 24  and the reference potential VSS. 
     The fifth sampling transistor SHR 3 -Tr is connected between the holding node ND 25  and the input node ND 20  connected to the signal line LSGN 10 . The fifth sampling transistor SHR 3 -Tr keeps the fifth signal holding capacitor CR 23  of the sample-and-hold part  232  selectively connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the holding node ND 25  during a global shutter period or signal holding capacitor clear period. The fifth sampling transistor SHR 3 -Tr is in the conduction state during a period in which, for example, a control signal SHR 3  is at the high level. The fifth signal holding capacitor CR 23  is connected between the holding node ND 25  and the reference potential VSS. 
     The sixth sampling transistor SHS 3 -Tr is connected between the holding node ND 26  and the input node ND 20  connected to the signal line LSGN 10 . The sixth sampling transistor SHS 3 -Tr keeps the sixth signal holding capacitor CS 23  of the sample-and-hold part  232  selectively connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the holding node ND 26  during a global shutter period or signal holding capacitor clear period. The sixth sampling transistor SHS 3 -Tr is in the conduction state during a period in which, for example, a control signal SHS 3  is at the high level. The sixth signal holding capacitor CS 23  is connected between the holding node ND 26  and the reference potential VSS. 
     The seventh sampling transistor SHR 4 -Tr is connected between the holding node ND 27  and the input node ND 20  connected to the signal line LSGN 10 . The seventh sampling transistor SHR 4 -Tr keeps the third signal holding capacitor CR 24  of the sample-and-hold part  232  selectively connected to the reading node ND 11  of the photoelectric conversion reading part  220  via the holding node ND 27  during a global shutter period or signal holding capacitor clear period. The third sampling transistor SHR 4 -Tr is in the conduction state during a period in which, for example, a control signal SHR 4  is at the high level. The seventh signal holding capacitor CR 24  is connected between the holding node ND 27  and the reference potential VSS. 
     The eighth sampling transistor SHS 4 -Tr is connected between the holding node ND 28  and the input node ND 20  connected to the signal line LSGN 10 . The eighth sampling transistor SHS 4 -Tr keeps the eighth signal holding capacitor CS 24  of the sample-and-hold part  232  selectively connected to the reading node ND 112  of the photoelectric conversion reading part  220  via the holding node ND 28  during a global shutter period or signal holding capacitor clear period. The eighth sampling transistor SHS 4 -Tr is in the conduction state during a period in which, for example, a control signal SHS 4  is at the high level. The eighth signal holding capacitor CS 24  is connected between the holding node ND 28  and the reference potential VSS. 
     Note that the first, second, third, fourth, fifth, sixth, seventh and eighth sampling transistors SHR 1 -Tr, SHS 1 -Tr, SHR 2 -Tr, SHS 2 -Tr, SHR 3 -Tr, SHS 3 -Tr, SHR 4 -Tr and SHS 4 -Tr are formed by MOS transistors, such as p-channel MOS (PMOS) transistors. 
     The first output part  233  includes a source follower transistor SF 2 R-Tr serving as a second source follower element for basically outputting the signal held in the first signal holding capacitor CR 21  as a signal at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 11  selectively through a selection transistor SEL 1 R-Tr. 
     The source follower transistor SF 2 R-Tr and the selection transistor SEL 1 R-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 11 . 
     The gate of the source follower transistor SF 2 R-Tr is connected to the holding node ND 21 , and the selection transistor SEL 1 R-Tr is controlled by a control signal SEL 1  applied to the gate thereof through a control line. The selection transistor SEL 1 R-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 1  is at the L level. In this way, the source follower transistor SF 2 R-Tr outputs, to the vertical signal line LSGN 11 , read-out voltage (VRST) of a column output corresponding to the voltage held in the first signal holding capacitor CR 21 . 
     The second output part  234  includes a source follower transistor SF 3 S-Tr serving as a third source follower element for basically outputting the signal held in the second signal holding capacitor CS 21  as a signal at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 12  selectively through a selection transistor SEL 2 S-Tr. 
     The source follower transistor SF 3 S-Tr and the selection transistor SEL 2 S-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 12 . 
     The gate of the source follower transistor SF 3 S-Tr is connected to the holding node ND 22 , and the selection transistor SEL 2 S-Tr is controlled by a control signal SEL 2  applied to the gate thereof through a control line. The selection transistor SEL 2 S-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 2  is at the L level. In this way, the source follower transistor SF 3 S-Tr outputs, to the vertical signal line LSGN 12 , read-out voltage (VSIG) of a column output corresponding to the voltage held in the second signal holding capacitor CS 21 . 
     The third output part  235  includes a source follower transistor SF 4 R-Tr serving as a fourth source follower element for basically outputting the signal held in the third signal holding capacitor CR 22  at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 11  selectively through the selection transistor SEL 3 R-Tr. 
     The source follower transistor SF 4 R-Tr and the selection transistor SEL 3 R-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 11 . 
     The gate of the source follower transistor SF 4 R-Tr is connected to the holding node ND 23 , and the selection transistor SEL 3 R-Tr is controlled by a control signal SEL 3  applied to the gate thereof through a control line. The selection transistor SEL 3 R-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 3  is at the L level. In this way, the source follower transistor SF 4 R-Tr outputs, to the vertical signal line LSGN 11 , read-out voltage (VRST) of a column output corresponding to the voltage held in the third signal holding capacitor CR 22 . 
     The fourth output part  236  includes a source follower transistor SF 5 S-Tr serving as a fifth source follower element for basically outputting the signal held in the fourth signal holding capacitor CS 22  at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 12  selectively through the selection transistor SEL 4 S-Tr. 
     The source follower transistor SF 5 S-Tr and the selection transistor SEL 4 S-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 12 . 
     The gate of the source follower transistor SFSS-Tr is connected to the holding node ND 24 , and the selection transistor SEL 4 S-Tr is controlled by a control signal SEL 4  applied to the gate thereof through a control line. The selection transistor SEL 4 S-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 4  is at the L level. In this way, the source follower transistor SF 5 S-Tr outputs, to the vertical signal line LSGN 12 , read-out voltage (VSIG) of a column output corresponding to the voltage held in the fourth signal holding capacitor CS 22 . 
     The fifth output part  237  includes a source follower transistor SF 6 R-Tr serving as a sixth source follower element for basically outputting the signal held in the fifth signal holding capacitor CR 23  at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 11  selectively through the selection transistor SEL 5 R-Tr. 
     The source follower transistor SF 6 R-Tr and the selection transistor SEL 5 R-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 11 . 
     The gate of the source follower transistor SF 6 R-Tr is connected to the holding node ND 25 , and the selection transistor SEL 5 R-Tr is controlled by a control signal SEL 5  applied to the gate thereof through a control line. The selection transistor SEL 5 R-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 5  is at the L level. In this way, the source follower transistor SF 6 R-Tr outputs, to the vertical signal line LSGN 11 , read-out voltage (VRST) of a column output corresponding to the voltage held in the fifth signal holding capacitor CR 23 . 
     The sixth output part  238  includes a source follower transistor SF 7 S-Tr serving as a seventh source follower element for basically outputting the signal held in the sixth signal holding capacitor CS 23  at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 12  selectively through the selection transistor SEL 6 S-Tr. 
     The source follower transistor SF 7 S-Tr and the selection transistor SEL 6 S-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 12 . 
     The gate of the source follower transistor SF 37 -Tr is connected to the holding node ND 26 , and the selection transistor SEL 6 S-Tr is controlled by a control signal SEL 6  applied to the gate thereof through a control line. The selection transistor SEL 6 S-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 6  is at the L level. In this way, the source follower transistor SF 7 S-Tr outputs, to the vertical signal line LSGN 12 , read-out voltage (VSIG) of a column output corresponding to the voltage held in the second signal holding capacitor CS 23 . 
     The seventh output part  239  includes a source follower transistor SF 8 R-Tr serving as an eighth source follower element for basically outputting the signal held in the seventh signal holding capacitor CR 24  at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 11  selectively through the selection transistor SEL 7 R-Tr. 
     The source follower transistor SF 8 R-Tr and the selection transistor SEL 7 R-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 11 . 
     The gate of the source follower transistor SF 8 R-Tr is connected to the holding node ND 27 , and the selection transistor SEL 7 R-Tr is controlled by a control signal SEL 7  applied to the gate thereof through a control line. The selection transistor SEL 7 R-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 7  is at the L level. In this way, the source follower transistor SF 6 R-Tr outputs, to the vertical signal line LSGN 11 , read-out voltage (VRST) of a column output corresponding to the voltage held in the seventh signal holding capacitor CR 24 . 
     The eighth output part  240  includes a source follower transistor SF 9 S-Tr serving as a ninth source follower element for basically outputting the signal held in the eighth signal holding capacitor CS 24  at a level determined by the held voltage in a global shutter period, and outputs the held signal to the vertical signal line LSGN 12  selectively through the selection transistor SEL 8 S-Tr. 
     The source follower transistor SF 9 S-Tr and the selection transistor SEL 8 S-Tr are connected in series between the reference potential VSS and the vertical signal line LSGN 12 . 
     The gate of the source follower transistor SF 9 S-Tr is connected to the holding node ND 28 , and the selection transistor SEL 8 S-Tr is controlled by a control signal SEL 8  applied to the gate thereof through a control line. The selection transistor SEL 8 S-Tr remains selected and in the conduction state during a selection period in which the control signal SEL 8  is at the L level. In this way, the source follower transistor SF 9 S-Tr outputs, to the vertical signal line LSGN 12 , read-out voltage (VSIG) of a column output corresponding to the voltage held in the eighth signal holding capacitor CS 24 . 
     As described above, in the solid-state imaging device  10 C relating to the fourth embodiment, in the voltage mode, the pixel signal is sampled by the signal holding part  230  serving as a pixel signal storage, which takes place in all of the pixels at the same time, and the signals obtained by converting the read-out signals held in the first, second, third, fourth, fifth, sixth, seventh and eighth signal holding capacitors CR 21 , CS 21 , CR 22 , CS 22 , CR 23 , CS 23 , CR 24  and CS 24  are read out to the vertical signal lines LSGN 11  and LSGN 12  and fed to the column reading circuit  40 . 
     In the solid-state imaging device  10 C relating to the third embodiment, one photoelectric conversion reading part  220  has charge storage parts of a plurality of photodiodes PD, and one signal holding part  230  serves as a memory part configured to hold the signals from the respective photodiodes PD globally. The signals held in the signal holding part  230  globally are read out sequentially (rolling read-out). 
       FIGS.  22 A and  22 B  show sequences of operations to illustrate a global shutter read-out operation performed by the solid-state imaging device  10 C relating to the fourth embodiment, in comparison with a rolling shutter read-out operation.  FIGS.  23 A,  23 B and  23 C  show example timing charts to illustrate a rolling shutter read-out operation.  FIGS.  24 A,  24 B and  24 C  show example timing charts to illustrate a global shutter read-out operation. 
       FIGS.  23 A and  24 A  show, as an example, timings of operations performed when the four photodiodes PD 10 , PD 11 , PD 12  and PD 13  are exposed under a single condition and signals are read simultaneously and in parallel.  FIGS.  23 B and  24 B  show, as an example, timings of operations performed when the four photodiodes PD 10 , PD 11 , PD 12  and PD 13  are exposed under different conditions and signals are read simultaneously and in parallel.  FIGS.  23 C and  24 C  show, as an example, timings of operations performed when the four photodiodes PD 10 , PD 11 , PD 12  and PD 13  are exposed under different conditions and signals are read simultaneously and in parallel while the read-out period can be taken care of by a single pair of memory capacitances. 
     When the example circuit configuration shown in  FIG.  21    is employed, the charges stored in the first photodiode PD 10  serving as a first photoelectric conversion element, the charges stored in the second photodiode PD 11  serving as a second photoelectric conversion element, the charges stored in the third photodiode PD 12  serving as a third photoelectric conversion element and the charges stored in the fourth photodiode PD 13  serving as a fourth photoelectric conversion element are respectively read out independently from each other. To begin with, the reset level of the floating diffusion FD 10  of the photoelectric conversion reading part  220  is read out, and is held in the signal holding capacitors CR 21 , CR 22 , CR 23  and CR 24  of the signal holding part  230 . Subsequently, a signal corresponding to the charges stored in the first photodiode PD 10  is read out and held in the signal holding capacitor CH 21  of the signal holding part  240 . 
     Subsequently, for example, the column reading circuit  40  amplifies and AD converts the read-out reset signal VRST and the read-out signal VSIG of the pixel signal pixout, which are differential signals and fed simultaneously and in parallel, and additionally calculates the difference between the signals {VRST−VSIG} and performs the CDS. 
     Similarly, a signal corresponding to the charges stored in the second photodiode PD 11  is read out, and held in the signal holding capacitor CH 22  of the signal holding part  230 . In other words, the signal from the second photodiode PD 11  is read, held, subjected to the CDS and AD conversion in the same manner. Similarly, a signal corresponding to the charges stored in the third photodiode PD 12  is read out and held in the signal holding capacitor CH 23  of the signal holding part  230 . In other words, the signal from the third photodiode PD 12  is read, held, subjected to the CDS and AD conversion in the same manner. Similarly, the signal corresponding to the charges stored in the fourth photodiode PD 13  is read out, and held in the signal holding capacitor CH 24  of the signal holding part  230 . In other words, the signal from the fourth photodiode PD 13  is read, held, subjected to the CDS and AD conversion in the same manner. As a result, the pixel signals read from the first, second, third and fourth photodiodes PD 10 , PD 11 , PD 12  and PD 13  including low noise can be processed as, for example, phase difference information without distortion. 
     The pixel gain can be controlled by controlling the storage transistor BIN 10 -Tr (BIN switch) in accordance with the level of the signal from the PD (illuminance), so that PDAF signal processing can be performed with a widened range, in other words, phase detection auto focus (PDAF) with HDR can be achieved. 
     As shown in  FIGS.  22 A,  23 A to  23 C , the starting time of the integration period depends on the position of the target pixel in the row direction (Y direction) in the existing rolling read-out. Therefore, the phase difference information also depends on the vertical coordinate. This is particularly problematic when a subject is moving at a high speed. The signals from the pixels at the upper and lower edges of the pixel array are read out at different timings. The phase difference information varies depending on the position of the subject, thereby distorting the phase difference information. In the case of a global shutter, on the other hand, this issue is solved as shown in  FIGS.  22 B and  24 A to  24 C , and no distortion is caused in the phase difference information even in video images. 
     In the fourth embodiment, the signal holding part  230  is provided in each pixel to serve as a memory part. This allows read-out information corresponding to the charges stored in the first photodiode PD 10  serving as the first photoelectric conversion element, the charges stored in the second photodiode PD 11  serving as the second photoelectric conversion element, the charges stored in the third photodiode PD 12  serving as the third photoelectric conversion element, and the charges stored in the fourth photodiode PD 13  serving as the fourth photoelectric conversion element to be captured substantially simultaneously. Since the photodiodes PD include the shutter gate transistors SG 10 -Tr, SG 11 -Tr, SG 12 -Tr and SG 13 -Tr serving as AB (anti-blooming) gates, a signal (for example, PD 11 ) can be saved from being mixed with another signal (PD 10 ) while being read out. This can contribute to achieving intended photoelectric conversion characteristics. 
     As described above, in the solid-state imaging device  10 C relating to the fourth embodiment, the pixel part  20 C includes pixels, and each pixel includes the photoelectric conversion reading part  220  and the signal holding part  230 . The solid-state imaging device  10 C is configured, for example, as a stacked CMOS image sensor capable of operating in a global shutter mode and substantially achieving a widened dynamic range and an enhanced frame rate. 
     More specifically, the solid-state imaging device  10 C relating to the fourth embodiment is capable of not only achieving a global shutter but also achieving a widened dynamic range and a raised frame rate since the charges overflowing from the photodiodes in the integration period can be used real time. Additionally, the fourth embodiment is capable of substantially achieving a widened dynamic range and a raised frame rate, achieving reduced noise, and maximizing the effective pixel region and value per cost. 
     Additionally, the solid-state imaging device  10 C relating to the fourth embodiment can prevent an increase in configuration complexity and reduction in area efficiency from the perspective of layout. 
     The solid-state imaging device  10 C relating to the fourth embodiment has a stacked structure of the first substrate (upper substrate)  110  and the second substrate (lower substrate)  120 . Accordingly, the fourth embodiment can maximize the value per cost since the first substrate  110  is basically formed only with NMOS elements and the pixel array can achieve a maximized effective pixel region. 
     The above has described the stacked solid-state imaging device capable of performing an analog global shutter. The present invention can be also applied to solid-state imaging devices having digital pixel (pixel) sensors (DPS). In the digital pixel sensors, for example, each pixel may additionally have an ADC including a comparator (and additionally a memory part). In this way, the sensors can realize a global shutter according to which the exposure to light can start and end at the same timing in all of the pixels of the pixel array part. 
     The solid-state imaging devices  10 ,  10 A,  10 B,  10 C described above can be applied, as an imaging device, to electronic apparatuses such as digital cameras, video cameras, mobile terminals, surveillance cameras, and medical endoscope cameras. 
       FIG.  25    shows an example configuration of an electronic apparatus including a camera system to which the solid-state imaging devices according to the embodiments of the present invention can be applied. 
     As shown in  FIG.  25   , the electronic apparatus  300  includes a CMOS image sensor  310  that can be constituted by the solid-state imaging devices  10 ,  10 A,  10 B and  10 C relating to the embodiments of the present invention. The electronic apparatus  300  further includes an optical system (such as a lens)  320  for redirecting the incident light to the pixel region of the CMOS image sensor  310  (to form a subject image). The electronic apparatus  300  includes a signal processing circuit (PRC)  330  for processing output signals of the CMOS image sensor  310 . 
     The signal processing circuit  330  performs predetermined signal processing on the output signals from the CMOS image sensor  310 . The image signals resulting from the processing in the signal processing circuit  330  can be handled in various manners. For example, the image signals can be displayed as a video image on a monitor having a liquid crystal display, printed by a printer, or recorded directly on a storage medium such as a memory card. 
     As described above, a high-performance, compact, and low-cost camera system can be provided that includes the solid-state imaging device  10 ,  10 A,  10 B,  10 C as the CMOS image sensor  310 . Accordingly, the embodiments of the present invention can provide for electronic apparatuses such as surveillance cameras and medical endoscope cameras, which are used for applications where the cameras are installed under restricted conditions from various perspectives such as the installation size, the number of connectable cables, the length of cables and the installation height. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               10 ,  10 A,  10 B,  10 C . . . solid-state imaging device 
               20  . . . pixel part 
             PD 10  . . . first photodiode 
             PD 11  . . . second photodiode 
             PD 12  . . . third photodiode 
             PD 13  . . . fourth photodiode 
             TG 0 -Tr . . . tenth transfer transistor 
             TG 11 -Tr . . . second transfer transistor 
             TG 12 -Tr . . . third transfer transistor 
             TG 13 -Tr . . . fourth transfer transistor 
             SG 10 -Tr . . . first shutter gate transistor 
             SG 11 -Tr . . . second shutter gate transistor 
             SG 122 -Tr . . . third shutter gate transistor 
             SG 13 -Tr . . . fourth shutter gate transistor 
             FD 10  . . . floating diffusion 
             RST 10 -Tr . . . reset transistor 
             SF 10 -Tr . . . source follower transistor 
             BIN 10 -Tr . . . storage transistor 
             CS . . . storage capacitor 
               220  . . . photoelectric conversion reading part 
               230  . . . signal holding part 
               30  . . . vertical scanning circuit 
               40  . . . output circuit 
               50  . . . timing control circuit 
               60  . . . reading part 
               300  . . . electronic apparatus 
               310  . . . CMOS image sensor 
               320  . . . optical system 
               330  . . . signal processing circuit (PRC)