Abstract:
An electric charge transfer apparatus comprises a plurality of vertical charge transfer devices, each of which transfers a signal electric charge, a plurality of charge-discharging circuits formed next to each vertical transfer device, each charge-discharging circuit discharging the signal electric charge transferred by at least either one of the adjoining vertical transfer devices, and an output circuit that outputs the signal electric charge transferred by the vertical charge transfer devices to an outside of the electric charge transfer apparatus. Appearance of a longitudinal line caused by left-behind electric charge which causes an electric potential barrier or an electric potential unevenness which exists in a transfer channel of a vertical electric charge transfer device included in an charge-discharging device with probability can be controlled.

Description:
[0001]    This application is based on Japanese Patent Application 2003-091783, filed on Mar. 28, 2003, and Japanese Patent Application 2003-091784, filed on Mar. 28, 2003, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    A) Field of the Invention  
           [0003]    This invention relates to a charge transfer device and a solid-state imaging device using the charge transfer device, and more specifically to an overflow drain structure of the charge transfer device.  
           [0004]    B) Description of the Related Art  
           [0005]    Conventionally, in a solid-state imaging device using a charge transfer device, for example, a signal charge of an arbitral vertical line of a photoelectric conversion element is thinning out alternatively by providing an overflow drain for draining a signal charge to a vertical charge transfer device. (For example, refer to Japanese Laid-Open Patent Hei6-338524.)  
           [0006]    FIGS.  7  are drawings showing a charge-discharging structure in the conventional charge transfer device of the solid-state imaging device. FIG. 7A is a plan view showing a charge-discharging structure in the conventional charge transfer device of the solid-state imaging device.  
           [0007]    A solid-state imaging device  300  is consisted of a multiplicity of photoelectric conversion elements  381  arranged in a tetragonal matrix, plurality of columns of vertical charge transfer devices (VCCD)  382 , a horizontal charge transfer device (HCCD)  383  and an output circuit  384 .  
           [0008]    A signal charge  387  stored in the photoelectric conversion elements  381  is vertically transferred from the upper side to the lower side in the drawing by the adjacent vertical charge transfer device  382 . The horizontal charge transfer device  383  receives the signal charges  387  transferred by plurality of columns of the vertical charge transfer devices  382  in parallel and transfers them to the output circuit  384  one after another. The output circuit  384  outputs the signal charges  387  transferred by the horizontal charge transfer device  383  to outside of the solid-state imaging device  300 .  
           [0009]    A charge-discharging device  390  is formed around the horizontal charge transfer device  383  near the lower end of the vertical charge transfer device  382 . The charge-discharging device  390  is consisted of a transfer circuit  391 , discharging control gate  393  and a overflow drain  395  and can discharge the signal charge  387  transferred by the vertical charge transfer device  382  to outside of the solid-state imaging device  300 .  
           [0010]    [0010]FIG. 7B is a schematic cross sectional view showing a structure of the charge-discharging device  390 .  
           [0011]    The transfer circuit  391  is consisted of n-type transfer channel (hereinafter called transfer channel)  391   c  formed on the surface of p-well (or p-type substrate)  385 , and transfer electrode  391   e  formed above transfer channel  391   c  with the insulating film  386  therebetween, and forms one transfer unit of the vertical charge transfer device  382 . A transfer voltage supplying line  392  supplies a control voltage φvn to the transfer electrode  391   e.    
           [0012]    The discharging control gate  393  is consisted of a transfer channel  393   c  which is an area between the n-type circuit formed as overflow drain  395  and the transfer channel  391   c  of the transfer circuit  391 , and a discharging control gate electrode  393   e  formed above discharging channel  393   c  with the insulated film  386  therebetween. Turning on/off of the discharging control gate  393  is controlled by control voltage φrc supplied by the discharging control voltage supply line  394 . Moreover, when the control voltage φrc is in a state of high level, the discharging control gate is ON, and when the control voltage φrc is in a state of low level, the discharging control gate is OFF.  
           [0013]    The overflow drain  395  is consisted of an n-type area formed on a surface of the p-well (or p-type substrate)  385  and is a drain for discharging the signal charge  387  to the outside. The drain voltage supplying line  396  supplies a drain voltage Vdr to the drain  395 .  
           [0014]    [0014]FIG. 7C is an electrical potential distribution map formed in a semiconductor of the charge-discharging device  390  shown in FIG. 7B.  
           [0015]    Electrical potential  397  shows channel electrical potential of the transfer channel, electrical potential  398 off shows channel electrical potential when the drain operation is turned off (control voltage φrc is in the state of low level), electrical potential  398 on shows channel electrical potential when the drain operation is turned on (control voltage φrc is in the state of high level), and electrical potential  399  shows drain electrical potential of the voltage overflow drain  395 .  
           [0016]    During the solid-state imaging elements  300  is being operated normally, the charge-discharging control electrode  393   e  maintains the state of turned-off (control voltage φrc is being at the low level), and the signal charge  387  transferred in the vertical charge transfer device  382  is not discharged to the outside, but is transferred to the horizontal charge transfer device  383 . Then, depending on necessity, when the signal charge  387  is transferred to the transfer channel  391   c , as shown with an dotted arrow in the drawing, by turning on the charge-discharging control electrode  393   e  (making the control voltage φrc at the high level), the signal charge  387  can be drained from the transfer channel  391   c  to the charge overflow drain  395  via the discharging channel  393   c.    
           [0017]    According to the above-described operation, since it is operated at once in plurality of the electric charge-discharging device  390  arranged in parallel, the signal charge of the one horizontal line of the photoelectric conversion element  381  that was chosen can be alternatively thinned out by changing on-off of electric charge drain control electrode  393   e  at specific timing.  
           [0018]    Generally, there may be a potential barrier as shown in FIG. 7C at a certain probability in the transfer channel  391   c , for example, by manufacturing unevenness. When there is a potential barrier  389 , the electric charge below a fixed amount cannot be drained by the charge-discharging device  395 . In the above-described electric charge-discharging device  390 , the signal electric charge  387  may be remained by the electric potential barrier  389  in the transfer channel  391   c  having the electric potential barrier  389  when the signal electric charge  387  is drained to the charge-discharging device  395  with the electric charge-discharging control electrode  393   e  turned on. The remained signal electric charge is output from the vertical charge transfer circuit  382  through the horizontal charge transfer device  383  after the drain operation finishes.  
           [0019]    For example, all the signal electric charges are drained to the charge-discharging device  395  by the electric charge-discharging device  390 , the remained electric charge is output from the vertical line having the electric potential barrier  389 , and it appears as a white line on a reproduced screen. This phenomenon will appear as a picture superimposed by the white line on a digital still camera etc. also in a case of the well-known process for thinning out one-half of the vertical scanning lines, and will worsen quality of image remarkably.  
         SUMMARY OF THE INVENTION  
         [0020]    It is an object of the present invention to control appearance of a longitudinal line by left-behind electric charge caused by an electric potential barrier or an electric potential unevenness which may exist in a transfer channel of a vertical electric charge transfer device included by an electric charge-discharging device.  
           [0021]    It is another object of the present invention to remarkably decrease generation of left-behind electric charge caused by the electric charge-discharging direction of an electric charge-discharging device.  
           [0022]    According to one aspect of the present invention, there is provided a n electric charge transfer apparatus, comprising: a plurality of vertical charge transfer devices, each of which transfers a signal electric charge; a plurality of charge-discharging circuits formed next to each vertical transfer device, each charge-discharging circuit discharging the signal electric charge transferred by at least either one of the adjoining vertical transfer devices; and an output circuit that outputs the signal electric charge transferred by the vertical charge transfer devices to an outside of the electric charge transfer apparatus.  
           [0023]    According to another aspect of the present invention, there is provided a solid-state imaging device, comprising: a semiconductor substrate; a plurality of photoelectric conversion elements formed on said semiconductor substrate; a plurality of vertical charge transfer device formed above said semiconductor substrate, which transfer signal electric charge photoelectric converted by said photoelectric conversion elements; a plurality of charge-discharging circuits formed next to each vertical transfer device, each charge-discharging circuit discharging the signal electric charge converted by the photoelectric conversion element at a predetermined position and transferred by at least either one of the adjoining vertical transfer devices; and an output circuit that outputs the signal electric charge transferred by the vertical charge transfer devices to outside.  
           [0024]    According to the present invention, appearance of a longitudinal line by the left-behind electric charge caused by an electric potential barrier or an electric potential unevenness which may exist in a transfer channel of a vertical electric charge transfer device included in an electric charge-discharging device can be controlled.  
           [0025]    According to still another aspect of the present invention, there is provided an electric charge transfer apparatus, comprising: a plurality of vertical charge transfer devices, each of which has plural lines of charge transfer electrodes and transfers signal electric charge; a plurality of charge-discharging circuits arranged to each line of the charge transfer electrodes, each of the charge-discharging circuit selectively discharging the signal electric charge transferred by the vertical charge transfer device to a discharging direction different from other charge-discharging circuit; and an output circuit that outputs the signal electric charge transferred by the vertical charge transfer devices to an outside of the electric charge transfer apparatus.  
           [0026]    According to further aspect of the present invention, there is provided an A solid-state imaging device, comprising: a semiconductor substrate; a plurality of photoelectric conversion elements formed on said semiconductor substrate; a plurality of vertical charge transfer device formed above said semiconductor substrate, which transfer signal electric charge photoelectric converted by said photoelectric conversion elements; a plurality of charge-discharging circuits arranged to each line of the charge transfer electrodes, each of the charge-discharging circuit selectively discharging the signal electric charge converted by the photoelectric conversion element at a predetermined position and transferred by the vertical charge transfer device to a discharging direction different from other charge-discharging circuit; and an output circuit that outputs the signal electric charge transferred by the vertical charge transfer devices to an outside of the electric charge transfer apparatus.  
           [0027]    According to the present invention, generation of left-behind electric charge caused by the electric charge-discharging direction of an electric charge-discharging device can be remarkably decreased.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 is a diagram showing an electric charge-discharging structure in a vertical charge transfer device  2  of a solid-state imaging device  101  according to a first embodiment of the present invention.  
         [0029]    [0029]FIG. 2 is a diagram showing an electric charge-discharging structure in the vertical charge transfer device  2  of a solid-state imaging device  102  according to a second embodiment of the present invention.  
         [0030]    [0030]FIG. 3 is a diagram showing an electric charge-discharging structure in a vertical charge transfer device  2   h  of a solid-state imaging device  103  according to a third embodiment of the present invention.  
         [0031]    [0031]FIG. 4 is a diagram showing an electric charge-discharging structure in the vertical charge transfer device  2   h  of a solid-state imaging device  104  according to a fourth embodiment of the present invention.  
         [0032]    [0032]FIG. 5 is a diagram showing an electric charge-discharging structure in the vertical charge transfer device  2  of the solid-state imaging device  101  according to a first embodiment of the present invention.  
         [0033]    [0033]FIG. 6 is a diagram showing an electric charge-discharging structure in the vertical charge transfer device  2  of the solid-state imaging device  102  according to a second embodiment of the present invention.  
         [0034]    [0034]FIG. 7 is a diagram showing an electric charge-discharging structure in the vertical charge transfer device of the conventional solid-state imaging device  300 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    FIGS.  1  are diagrams showing an electric charge-discharging structure in a vertical charge transfer device  2  of a solid-state imaging device  101  according to a first embodiment of the present invention.  
         [0036]    [0036]FIG. 1A is a plan view showing an electric charge flow structure in the vertical charge transfer device  2  of the solid-state imaging device  101 .  
         [0037]    The solid-state imaging device  101  is consisted of a multiplicity of photoelectric conversion elements  1  arranged in a tetragonal matrix, plurality of columns of the vertical charge transfer devices (VCCD)  2  formed adjacent to each column of the photoelectric conversion elements  1 , a horizontal charge transfer device (HCCD)  3  formed at the lower end of the plurality of columns of the vertical charge transfer devices  2  and an output circuit  4  connected to the end of horizontal charge transfer device.  
         [0038]    A signal electric charge  7  stored in the photoelectric conversion elements  1  is transferred from upper side of the drawing to the lower side in vertical by the adjacent vertical charge transfer device  2 . The horizontal charge transfer device  3  receives the transferred signal electric charge  7  in parallel by the plural columns of the vertical charge transfer devices  2  to transfer to the output circuit  4  in sequence. The output circuit  4  outputs the signal electric charge  7  to the outside of the solid-state imaging device  101  by the horizontal charge transfer device  3 .  
         [0039]    A first charge-discharging device  10  and a second charge-discharging device  20  are formed serially on the same side at the end of the vertical charge transfer device  2  near the horizontal charge transfer device  3 . The first charge-discharging device  10  is consisted of a transfer circuit  11 , a discharging control gate  13  and an overflow drain  15  and can selectively discharge the signal electric charge  7  photo-electric converted at a predetermined position and transferred in the vertical charge transfer device  2  to the outside of the solid-state imaging device  101 . The second charge-discharging device  20  is consisted of a transfer circuit  21 , a discharging control gate  23  and an overflow drain  25  and can discharge the signal electric charge  8  left by the charge-discharging device  10  to the outside the solid-state imaging device  101 .  
         [0040]    [0040]FIG. 1B is a schematic cross sectional view showing a structure of the first charge-discharging device  10 .  
         [0041]    The transfer circuit  11  is consisted of an n-type transfer channel (hereinafter called just the transfer channel)  11   c  formed on a surface of a p-well (or a p-type substrate)  5  and a transfer electrode  11   e formed upper side of the transfer channel  11   c  with an insulating film  6  formed therebetween, and forms one transfer unit of the vertical charge transfer device  2 . A transfer voltage supplying line  12  supplies a first transfer control voltage φvn 1  to the transfer electrode  11   e.    
         [0042]    The discharging control gate  13  is consisted of a discharging channel  13   c  which is an area between the n-type area formed as a discharging circuit  15  and a transfer channel  11   c  of the transfer circuit  11 , and a discharging control gate electrode  13   e  formed above discharging channel  13   c  with the insulated film  6  therebetween. Turning on/off of the discharging control gate  13  is controlled by first discharging control voltage φrc 1  supplied by the discharging control voltage supplying line  14 . Moreover, when the first discharging control voltage φrc 1  is in a state of high level, it is turned on, and when the discharging control voltage φrc 1  is in a state of low level, it is turned off.  
         [0043]    The overflow drain  15  is consisted of an n-type area formed on the surface of the p-well (or a p-type substrate) and is a drain for discharging signal electric charge  7  to the outside. The drain voltage supplying line  16  supplies the first drain voltage Vdr 1  to the overflow drain  15 .  
         [0044]    [0044]FIG. 1C is an electric potential distribution map formed in a semiconductor of the first charge-discharging device  10  shown in FIG. 1B.  
         [0045]    Each of electric potential  17 , electric potential  180 off, electric potential  18 on and electric potential  19  indicates channel electric potential of the transfer channel, channel electric potential at a time of drain operation off (when the control voltage  13   c  is at the low level) of the discharging channel  13   c , channel electric potential at a time of drain operation on (when control voltage φrc 1  is at the high level) of the discharging channel  13   c  and drain electric potential of the charge-discharging device  15 .  
         [0046]    During a normal operation of the solid-state imaging elements  101 , the charge-discharging control electrode  13   e  maintains the state of turned-off (control voltage φrc 1  is at the low level), and the signal charge  7  transferred at the vertical charge transfer device  2  is not discharged to the outside, but is transferred to the horizontal charge transfer device  3 . Then, depending on necessity, when the signal charge  7  is transferred to the transfer channel  11   c , as shown with a dotted arrow in the drawing, by turning on the charge-discharging control electrode  13   e  (making the control voltage φrc 1  at the high level), the signal charge  7  can be drained from the transfer channel  11   c  to the charge overflow drain  15  via the discharging channel  13   c.    
         [0047]    According to the above-described operation, the signal charge photoelectric converted by the photoelectric conversion element  1  at a specific timing can be alternatively thinned out by changing on-off of electric charge drain control electrode  13   e  at the specific timing.  
         [0048]    Moreover, for example, when an electric potential barrier  9  exists in the transfer channel  11   c  of the first charge-discharging device  10 , all of the signal electric charge  7  cannot be drained, and left-behind electric charge  8  (FIG. 1E) may be left in the transfer channel  11   c.    
         [0049]    [0049]FIG. 1D is a schematic cross sectional view showing structure of the second charge-discharging device  20 .  
         [0050]    The transfer circuit  21  is consisted of a n-type transfer channel (hereinafter called just the transfer channel)  21   c  formed on the surface of the p-well (or the p-type substrate)  5  and a transfer electrode  21   e formed upper side of the transfer channel  21   c  with the insulating film  6  therebetween, and forms one transfer unit of the vertical charge transfer device  2 . A transfer voltage supplying line  22  supplies a second transfer control voltage φvn 2  to the transfer electrode  21   e.    
         [0051]    The discharging control gate  23  is consisted of a discharging channel  23   c  which is an area between the n-type area formed as discharging circuit  25  and the transfer channel  21   c  of the transfer circuit  21 , and a discharging control gate electrode  23   e  formed above the discharging channel  23   c  with the insulated film  6  therebetween. Turning on/off of the discharging control gate  23  is controlled by second discharging control voltage φrc 2  supplied by the discharging control voltage supplying line  24 . Moreover, when the second discharging control voltage φrc 2  is in a state of the high level, the discharging control gate  23  is turned on, and when the discharging control voltage φrc 2  is in a state of the low level, it is turned off.  
         [0052]    The overflow drain  25  is consisted of an n-type area formed on the surface of the p-well (or a p-type substrate) and is a drain for discharging the left-behind electric charge  8  to the outside. The drain voltage supplying line  26  supplies the second drain voltage Vdr 2  to the overflow drain  15 .  
         [0053]    [0053]FIG. 1E is an electric potential distribution map formed in the semiconductor of the second charge-discharging device  20  shown in FIG. 1D.  
         [0054]    Each of electric potential  27 , electric potential  28 off, electric potential  28 on and electric potential  29  indicates channel electric potential of the transfer channel, channel electric potential at a time of drain operation off (when the control voltage φrc 2  is at the low level) of the discharging channel  23   c , channel electric potential at a time of drain operation on (when control voltage φrc 2  is at the high level) of the discharging channel  23   c  and drain electric potential of the charge-discharging device  25 .  
         [0055]    During a normal operation of the solid-state imaging elements  101 , the charge-discharging control electrode  23   e  maintains the state of being turned-off (control voltage φrc 2  is at the low level), and the signal charge  7  that is transferred in the vertical charge transfer device  2  is not discharged to the outside, but is transferred to the horizontal charge transfer device  3 . Then, after the electric charge-discharging operation (after transferring the left-behind electric charge  8  to the transfer channel  21   c ) by the first charge-discharging device  10 , as shown with an dotted arrow in the drawing, by turning on the charge-discharging control electrode  23   e  (making the control voltage φrc 2  being high level), the signal charge  8  can be drained from the transfer channel  21   c  to the charge overflow drain  25  via the discharging channel  13   c.    
         [0056]    As described in the above, in the first embodiment of the present invention, by providing the second charge-discharging device  20  under the first charge-discharging device  10 , the left-behind electric charge  8  left by the first charge-discharging device  10  can be drained by the second charge-discharging device  20 . Therefore, the left-behind electric charge  8  can be cleared almost completely.  
         [0057]    Since it is considered that the probability that the electric potential barrier  9  exists in the first charge-discharging device  10 , and the probability that the electric potential barrier  9  exists in the second charge-discharging device  20  are equivalent, the left-behind electric charge probability of the electric charge-discharging by the first embodiment of the present invention is not “0.” Although, when the left-behind electric charge probability of each of the charge-discharging devices  10  and  20  is “{fraction (1/100)}”, the probability that an electric charge will be left in both the first charge-discharging device  10  and the second charge-discharging device  20  becomes “{fraction (1/10,000)}”, and can obtain the large improvement effect.  
         [0058]    Moreover, although in the embodiment of the present invention, only the first charge-discharging device  10  and the second charge-discharging device  20  are provided, a third charge-discharging device can be further provided. In this case, when the left-behind electric charge probability of each charge-discharging device is “{fraction (1/100)}”, the probability that an electric charge will be left in all the charge-discharging devices becomes “{fraction (1/1,000,000)}”, and charge-discharging device probability of electric charge-discharging will be near “0” substantially.  
         [0059]    Moreover, the structure shown in FIG. 1A is the same as well-known square lattice arranged CCD solid-state imaging device except the first charge-discharging device  10  and the second charge-discharging device  20 .  
         [0060]    FIGS.  2  are diagrams showing an electric charge-discharging structure in the vertical charge transfer device  2  of a solid-state imaging device  102  according to a second embodiment of the present invention.  
         [0061]    [0061]FIG. 2A is a plan view showing structure of charge-discharging device in the vertical charge transfer device  2  of a solid-state imaging device  102 . The solid-state imaging device  102  is different from the above-described first embodiment in a point that the electric charge-discharging directions of the first charge-discharging device  10  and the charge-discharging device  30 . Since other structure and operation is the same as the first embodiment, the explanations of them will be omitted.  
         [0062]    [0062]FIG. 2B is a schematic cross sectional view showing structure of the first charge-discharging device  10 , and FIG. 2D is a schematic cross sectional view showing structure of a second charge-discharging device  30 . Since structure of the first charge-discharging device  10  is the same as the structure of the charge-discharging device  10  shown in FIG. 1B, the explanation for it is omitted. Also, the detailed explanation of the second charge-discharging device  30  will be omitted because only difference between the second charge-discharging device  20  shown in FIG. 1D and the second charging discharging device  30  is that local relationship among each parts are mirror symmetries.  
         [0063]    As shown in FIG. 2B and FIG. 2D, the first charge-discharging device  10  has the discharging control gate  13  positioned on the left side of the transfer device  11 , and the signal electric charge  7  is discharged to the left-side drain  15 . On the other hand, the second charge-discharging device  30  has the discharging control gate  33  positioned on the right side of the transfer device  31 , and left-behind electric charge  8  is discharged to the right-side drain  35 .  
         [0064]    As described in the above, an advantage of making discharging directions of the first charge-discharging device  10  and the second charge-discharging device  30  symmetry is explained by referring electric potential distribution maps shown in FIG. 2C and FIG. 2E.  
         [0065]    When the electric potential barrier  9  is extended to a vertical direction in vertical charge transfer device  2  (transfer channels  11   c  and  31   c ), as shown in the drawing, it exists discharging channel  13   c  side in the transfer channel  11   c , and it exists opposite side of the discharging channel  33   c  in the transfer channel  31   c . In this case, when charge-discharging direction of the first charge-discharging device  10  and the second charge-discharging device  20  is same, the left-behind electric charge cannot be avoided. However, as in this second embodiment, the left-behind electric charge  8  can be discharged to the overflow drain  35  where is the opposite side of the first charge-discharging device  10  by making the charge-discharging directions of the first charge-discharging device  10  and the second charge-discharging device  30  reversed.  
         [0066]    Therefore, according to the second embodiment of the present invention, when the potential barrier which has a spacial correlation exists, the left-behind electric charge by the charge-discharging device can be cut down sharply.  
         [0067]    FIGS.  3  are diagrams showing an electric charge-discharging structure in a vertical charge transfer device  2   h  of a solid-state imaging device  103  according to a third embodiment of the present invention.  
         [0068]    [0068]FIG. 3A is a plan view showing a charge-discharging structure in the vertical charge transfer device  2  of a solid-state imaging device  3 .  
         [0069]    Photoelectric conversion elements  1   h  of the solid-state imaging device  103  are disposed in a matrix with a so-called pixel interleaved arrangement (PIA) or the honeycomb arrangement. That is, the photoelectric conversion elements  1   h  in the even number rows (lines) and in the odd number rows (lines) are shifted in the horizontal direction by about a half pitch of the photoelectric conversion elements  1   h , and the photoelectric conversion elements  1   h  in the even number columns and in the odd number columns are shifted in the vertical direction by about a half pitch of photoelectric conversion elements  1   h . The phrase “about a half pitch of photoelectric conversion elements in the column (row) direction” is intended to include also the pitch regarded as substantially equal to the half pitch from the performance and image quality although this pitch is different from the correct half pitch because of manufacture tolerances, rounding errors of pixel positions to be caused by design or mask manufacture, or the like.  
         [0070]    The photoelectric conversion elements  1   h  are diamond shaped fundamentally (strictly speaking, “an octagon”) and have a shape wherein the vertices are chamfered. By adapting diamond-shaped pixels with honeycomb arrangement, invalid region can be deceased, and wide transfer circuit of the vertical charge transfer device (VCCD)  2   h  can be formed. Plural columns of the vertical charge transfer devices (VCCD)  2   h  arranged along the photoelectric conversion elements  1   h  of each column are formed by slaloming along the shape of photoelectric conversion elements  1   h.    
         [0071]    The signal electric charges  7  stored in the photoelectric conversion elements  1   h  are transferred from upper side to downward vertically by the adjacent vertical charge transfer device  2   h . The horizontal charge transfer device  3  receives the signal electric charges  7  transferred by the plural columns of the vertical charge transfer devices  2  in parallel and transfers to output circuit  4  in sequence. The output circuit  4  outputs the signal electric charges  7  transferred by the horizontal charge transfer device  3  to the outside of the solid-state imaging device  103 .  
         [0072]    By providing a transfer line  71  that is inclined to the verticality, as shown in the drawing, near the end of the vertical charge transfer device  2   h  close to the horizontal charge transfer device  3 , two columns of the adjacent vertical charge transfer devices  2   h  are made to be closer and the first charge-discharging device  40  is formed in an enlarged space. The first charge-discharging device  40  is consisted of the transfer circuits  41 L and  41 R of the vertical charge transfer device  2   h  on either side, discharging controlling gates  43 L and  43 R on either side and one overflow drain  45 , and can discharge the signal electric discharge  7  transferred at the vertical charge transfer devices  2   h  on either side that is adjacent horizontally to the outside the solid-state imaging device  103 . That is, adjacent two columns of the vertical charge transfer devices  2   h share one overflow drain  45 .  
         [0073]    Moreover, as shown in the drawing, a transfer line  72  that is inclined to the opposite direction of the transfer line  71  vertically is provided in the latter line of the first charge-discharging device  40 , and a second charge-discharging device  50  with different electric discharging direction from the first charge-discharging device  40  in a space that is enlarged by the inclined transfer line  72 .  
         [0074]    [0074]FIG. 3B is a schematic cross sectional view showing structure of the first charge-discharging device  40 . Moreover, the explanation for the second charge-discharging device  50  will be omitted because the only difference between the second charge-discharging device  50  and the first charge-discharging device  40  is that the second charge-discharging device  50  corresponds to the vertical charge transfer device  2   h  shifted one column to a horizontal direction and other structure and operation are almost the same.  
         [0075]    Discharging control gate  43 L and  43 R, each of which is consisted of discharging control electrode  43   e  and discharging channel  43   c  are formed on both sides of the overflow drain. Moreover, transfer circuits  41 L and  41 R each of which is consisted of transfer electrode  41   e and transfer channel  41   c  are formed to the outside of the discharging control gate  43 L and  43 R. The signal electric charges  7  of the transfer circuit  41 L and  41 R are discharged by the discharging control gates  43 L and  43 R which are turned on at the same time from the same overflow drain  45 .  
         [0076]    [0076]FIG. 3C is an electric potential distribution map formed in the semiconductor of the first charge-discharging device  40  shown in FIG. 3B.  
         [0077]    Electrical potential  47  indicates channel electrical potential of the transfer channel  41   c . Electrical potential  480 off indicates channel electrical potential at a time of discharging operation is turned off (when control voltage φrc 3  is at the low level) of the discharging channel  43   c . Electrical potential  48 on indicates channel electrical potential at a time of discharging operation (when the control voltage φrc 3  is at the high level) of the discharging channel  43   c . Electrical potential  49  indicates drain electrical potential of the charge-discharging device  45 .  
         [0078]    When the signal electric charges are transferred to the transfer channels on right and left sides, the signal electric charges  7  can be discharged from the transfer channels on both sides to the charge-discharging device  45  via the discharging channels  43   c  on right and left sides as shown with dotted arrows in the drawing by making right and left side of the electric charge control electrodes  43   e  turned on (making the control voltage φrc 3  at the high level).  
         [0079]    In the second electrical charge-discharging device  50 , the same operation is executed, and the left-behind electric charge of the first electric charge-discharging device can be discharged to an opposite direction of the first electric charge-discharging device  40 .  
         [0080]    As described in the above, in the third embodiment of the present invention, since two columns of the vertical charge transfer devices  2   h  share one overflow drain  45 , the number of drains will be half, and intensity of the horizontal direction can be increased remarkably. Also, left-behind electric charge by the charge-discharging device can be decreased remarkably when the electric potential barrier having special correlation exists as same as the above-described second embodiment by providing the second charge-discharging device  50  that discharges to the different direction at lower line of the first charge-discharging device  40 .  
         [0081]    Moreover, in the third embodiment, although the number of the drains will be decreased more than the before-described first and second embodiments, actually the number of the drains for the vertical charge transfer device on both sides will be about a half.  
         [0082]    [0082]FIG. 4 is a diagram showing an electric charge discharging structure in the vertical charge transfer device  2   h  of a solid-state imaging device  104  according to a fourth embodiment of the present invention. Detailed explanations for the structure and functions similar to the before-described third embodiment will be omitted, and only a different point will be explained below.  
         [0083]    The difference from the before-described third embodiment is that the first charge-discharging device  60  and the second charge-discharging device  70  are formed in a same space. In this case, as shown in the drawing, the overflow drains of the first charge-discharging device  60  and the second charge-discharging device  70  is combined together, and it can be one overflow drain  65 . Therefore, according to the fourth embodiment of the present invention, not only intensity of the horizontal direction, but intensity of the vertical direction can be increased remarkably.  
         [0084]    As described in the above, according to the first to the fourth embodiments of the present invention, the left-behind electric charges that will be a problem when signal electric charges transferred at the vertical charge transfer device are selectively discharged can be decreased remarkably by providing plurality of the charge-discharging devices for one vertical charge transfer device.  
         [0085]    For example, when a probability of generating the left-behind electric charge at one charge-discharging device is η, a probability of the left-behind electric charge at a time of providing n number of charge-discharging devices decreases to the n-th power of η. Here, n&lt;1 and n≧2 (n indicates an integer).  
         [0086]    Moreover, in the above-described first to fourth embodiments, the examples providing two charge-discharging devices have been explained. Moreover, providing more than two charge-discharging devices can further decrease the probability of existence of the left-behind electric charge.  
         [0087]    Also, in the above-described first and second embodiments, although the CCD solid-state imaging device in a tetragonal matrix is explained as the examples, and in the third and fourth embodiment, the CCD solid-state imaging device in a pixel interleaved arrangement is explained as the examples, the CCD solid-state imaging device in a pixel interleaved arrangement can be adopted for the first and the second embodiments, and the CCD solid-state imaging device in a tetragonal matrix can be adopted for the third and the fourth embodiments.  
         [0088]    FIGS.  5  are diagrams showing an electric charge discharging structure in the vertical charge transfer device  82  of the solid-state imaging device  201  according to a first embodiment of the present invention.  
         [0089]    [0089]FIG. 5A is a plan view showing the electric charge-discharging structure in a vertical charge transfer device  82  of a solid-state imaging device  201 .  
         [0090]    The solid-state imaging device  201  is consisted of a multiplicity of photoelectric conversion elements  81  arranged in a tetragonal matrix, plurality of columns of vertical charge transfer devices (VCCD)  82  formed adjacent to each column of the photoelectric conversion elements  81 , a horizontal charge transfer device (HCCD)  83  formed at the end of the plurality of columns of vertical charge transfer devices  82  and an output circuit  84  connected to the end of the horizontal charge transfer device.  
         [0091]    Signal electric charges  87  stored in the photoelectric conversion elements  81  are transferred from upper side of the diagram to the lower side in vertical by the adjacent vertical charge transfer device  83 . The horizontal charge transfer device  83  receives the transferred signal electric charges  87  in parallel by the plural columns of the vertical charge transfer devices  82  to transfer to an output circuit  84  in sequence. The output circuit  84  outputs the signal electric charges  87  to the outside of the solid-state imaging device  201  by the horizontal charge transfer device  83 .  
         [0092]    A first electric charge-discharging device  210  and a second electric charge-discharging device  220  are formed serially at the end of the vertical charge transfer device  82  near the horizontal charge transfer device  83 .  
         [0093]    The first electric charge-discharging device  210  is consisted of a transfer circuit  211 , an discharging control gate  213  and an overflow drain  215  and can selectively discharge the signal electric charge  87  photo-electric converted at a predetermined position and transferred in the vertical charge transfer device  82  to the outside the solid-state imaging device  201 .  
         [0094]    The second charge-discharging device  220  is consisted of a transfer circuit  211 , a discharging control gate  213 R and an overflow drain  215 R and can discharge the signal electric charge  87  photo-electric converted at the same position of the signal electric charge  87  discharged at the charge-discharging device  210  to the outside the solid-state imaging device  201 .  
         [0095]    [0095]FIG. 5B is a schematic cross sectional view showing a structure of the first charge-discharging device  210  and the second charge-discharging device  220 .  
         [0096]    The transfer circuit  211  is consisted of an n-type transfer channel (hereinafter called just the transfer channel)  211   c  formed on a surface of a p-well (or a p-type substrate)  85  and a transfer electrode  211   e  formed upper side of the transfer channel  211   c  with an insulating film  86  therebetween, and forms one electric charge transfer unit of the vertical charge transfer device  82 . A transfer voltage supplying line  212  supplies a first transfer control voltage φvn 1  to the transfer electrode  211   e . Moreover, the transfer circuit  211  is a part of the electric charge-discharging device  210  and the second charge-discharging device  220 .  
         [0097]    The discharging control gate  213 L is consisted of a discharging channel  213 Lc which is an area between the n-type area formed as overflow drain  215 L and a transfer channel  211   c  of the transfer circuit  211 , and a discharging control gate electrode  213 Le formed above the discharging channel  213 Lc with the insulated film  86  therebetween.  
         [0098]    A discharging control gate  213 R is consisted of a discharge channel  213 Rc which is an area between the n-type region formed as the overflow drain  215 R and the transfer channel  211   c  of the transfer circuit  211 , and a discharging control gate electrode  213 Re formed above discharging channel  213 Rc with the insulated film  86  therebetween.  
         [0099]    Turning on/off of the discharging control gates  213 L and  213 R are controlled by discharging control voltage φrc supplied by the discharging control voltage supplying line  214 . Moreover, when the first discharging control voltage φrc 1  is at the high level, the discharging control gates  213 L and  213 R are turned on, and when the discharging control voltage φrc 1  is at the low level, the discharging control gates  213 L and  213 R are turned off.  
         [0100]    The overflow drains  215 L and  215 R, each of which is consisted of an n-type area formed on the surface of the p-well (or a p-type substrate) and is a drain for discharging signal electric charges  87  to the outside. The drain voltage supplying line  216  supplies the drain voltage Vdr to the overflow drains  215 L and  215 R.  
         [0101]    [0101]FIG. 5C is an electric potential distribution map formed in a semiconductor of the first charge-discharging device  210  shown in FIG. 5B.  
         [0102]    Each of electric potential  217 , electric potential  2180 off, electric potential  218 on and electric potential  219  indicates channel electric potential of the transfer channel, channel electric potential at a time of drain operation off (when the control voltage φrc is low level) of the discharging channels  213 Lc and  213 Rc, channel electric potential at a time of drain operation on (when control voltage φrc is high level) of the discharging channels  213 Lc and  213 Rc and drain electric potential of the charge-discharging device  215 L and  215 R.  
         [0103]    During a normal operation of the solid-state imaging elements  201 , the charge-discharging control electrodes  213 Le and  213 Re maintain the state of turned-off (control voltage φrc is at the low level), and the signal charges  87  transferred at the vertical charge transfer device  82  are not discharged to the outside, but are transferred to the horizontal charge transfer device  83 . Then, depending on necessity, when the signal charges  87  are transferred to the transfer channel  211   c , as shown with dotted arrows in the drawing, by turning on the charge-discharging control electrodes  213 Le and  213 Re (making the control voltage φrc at the high level), the signal charges  87  can be discharged from the transfer channel  211   c  to the charge overflow drains  215 L and  215 R on right and left sides via the discharging channels  213 Lc and  213  Rc.  
         [0104]    According to the above-described operation, the signal charges photoelectric converted at the photoelectric conversion element  81  at a specific timing can be alternatively thinned out by changing on-off of electric charge drain control electrodes  213 Le and  213 Re at the specific timing.  
         [0105]    For example, as shown in the drawing, an electrical potential barrier  89  exists in the first charge-discharging device side  210  in a common transfer channels, the signal electric charge below fixed quantity cannot be discharged to the overflow drain  215 L. However, in the process which results in the overflow drain  215 R of the second electric charge-discharging circuit  220 , the electrical potential barrier  89  does not exist, and the signal electric charge below fixed quantity can be discharged through overflow drain  215 R.  
         [0106]    Moreover, for example, even when the potential barrier  9  exists in the center mostly in the common transfer channels  211   c , the signal electric charge below the fixed quantity from the first electric charge-discharging device  210  side is discharged through overflow drain  215 L, and the signal electric charge below the fixed quantity from the second electric charge-discharging circuit  220  side is discharged through overflow drain  215 R.  
         [0107]    As described in the above, according to the fifth embodiment of the present invention, even if the electrical potential barrier  89  exists in the common transfer channel  211   c , the signal electric charge below the fixed quantity can be discharged through either one of the first charge-discharging device  210  side and the second charge-discharging device  220  side on which the electrical potential barrier  89  does not exist. Therefore, left-behind electric charge can be removed.  
         [0108]    Moreover, the structure shown in FIG. 5A is similar to the well-known CCD solid-state imaging device in a tetragonal matrix except the first charge-discharging device  210  and the second charge-discharging device  220 .  
         [0109]    [0109]FIG. 6 is a diagram showing an electric charge-discharging structure in the vertical charge transfer device  82   h  of the solid-state imaging device  202  according to a sixth embodiment of the present invention.  
         [0110]    Photoelectric conversion elements  81   h  of the solid-state imaging device  202  are disposed in a matrix with a so-called pixel interleaved arrangement or the honeycomb arrangement. That is, the photoelectric conversion elements  81   h  in the even number rows (lines) and in the odd number rows (lines) are shifted in the horizontal direction by about a half pitch of photoelectric conversion elements  81   h , and the photoelectric conversion elements  81   h  in the even number columns and in the odd number columns are shifted in the vertical direction by about a half pitch of photoelectric conversion elements  81   h.    
         [0111]    The photoelectric conversion elements  81   h  are diamond shape fundamentally and have a shape wherein the vertices are chamfered. By adapting diamond-shaped pixels with honeycomb arrangement, invalid region can be deceased, and wide transfer circuit of the vertical charge transfer device (VCCD)  82   h  can be formed. Plural columns of the vertical charge transfer devices (VCCD)  82   h  arranged along the photoelectric conversion elements  1   h  of each column are formed by slaloming along the shape of photoelectric conversion elements  81   h.    
         [0112]    The signal electric charges  87  stored in the photoelectric conversion elements  81   h  are transferred from upper side to downward vertically by the adjacent vertical charge transfer device  82   h . The horizontal charge transfer device  83  receives the signal electric charges  87  transferred by the plural columns of the vertical charge transfer device  82  in parallel and transfers to output circuit  84  in sequence. The output circuit  84  outputs the signal electric charges  87  transferred by the horizontal charge transfer device  83  to the outside the solid-state imaging device  202 .  
         [0113]    By providing a transfer lines  271 L and  271 R that is inclined to the verticality as shown in the diagram around the horizontal charge transfer device  83  at the end of the vertical charge transfer device  82   h , the vertical charge transfer devices  82   h  horizontally adjoining each other are made closer, and the first charge-discharging device  230  is formed in an enlarged space. The first charge-discharging device  230  is consisted of the inclined transfer circuits  221 L and  221 R of the vertical charge transfer device  82   h  on either side, discharging controlling gate  223 L and one overflow drain  225 L, and can discharge the signal electric discharge  87  transferred at the vertical charge transfer devices  82   h  on either side that is adjacent horizontally to the outside the solid-state imaging device  202 . That is, adjacent two columns of the vertical charge transfer devices  82   h  share one overflow drain  225 .  
         [0114]    Moreover, as shown in the drawing, a inclined transfer circuit  221 L and  221 R of the first charge-discharging device is inclined to the opposite direction of the transfer lines  271 L and  271 R vertically, and a second charge-discharging device  240  with different electric discharging direction from the first charge-discharging device  230  in a space that is enlarged by the inclined transfer lines  221 L and  221 R.  
         [0115]    The second charge-discharging device  240  is consisted of the inclined transfer circuits  221 L and  221 R of the vertical charge transfer device  82   h  on both sides, discharging control gate  223 R and one overflow drain  225 R, and can discharge the signal electric charge  87  transferred at the vertical charge transfer devices on both sides which are adjacent horizontally to the outside the solid-state imaging device  202 . That is, it has structure that adjacent two columns of vertical charge transfer devices  82   h  share one overflow drain.  
         [0116]    Discharging principles and the like of the above-described charge-discharging device is almost same as the before-described fifth embodiment, and detailed explanation will be omitted.  
         [0117]    As described in the above, according to the sixth embodiment of the present invention, since two columns of the vertical charge transfer devices  82   h  share one overflow drain  225  ( 225 L or  225 R), the number of the drains decreases half, and intensity of the horizontal direction will be increased.  
         [0118]    Also, the left-behind electric charge with charge-discharging direction of the charge-discharging device can be removed as same as the above-described fifth embodiment by providing the second charge-discharging device  240  that has different charge-discharging direction on the charge transfer line (transfer channel)  211  that is same as the first charge-discharging device  230 .  
         [0119]    Moreover, although the number of the drains will be decreased than the before-described fifth embodiment, actually it may be possible that the vertical charge transfer devices on both sides cannot share the overflow drain, and the number of the drains for the vertical charge transfer device on both sides will not be a perfect ½, but will be about a half.  
         [0120]    As described in the above, according to the embodiments of the present invention, the left-behind electric charge that will be a problem at a time of discharging signal electric charge to be transferred at the vertical charge transfer device can be decreased remarkably by providing plurality of the charge-discharging devices with different charge-discharging direction for one vertical charge transfer device.  
         [0121]    For example, when probability of generating left-behind electric charge at one charge-discharging device is η, probability of left-behind electric charge at a time of providing n number of charge-discharging devices decreases to the n-th power of η. Here, n&lt;1 and n≧2 (n indicates an integer).  
         [0122]    Moreover, in the above-described first to fourth embodiments, the examples with two charge-discharging devices have been explained. Moreover, probability of existence of the left-behind electric charge can be decreased by providing more than two charge-discharging devices.  
         [0123]    Also, in the above-described fifth embodiment, the CCD solid-state imaging device in a tetragonal matrix has been used as an example, and in the sixth embodiment, the CCD solid-state imaging device in a pixel interleaved arrangement has been used as an example. CCD solid-state imaging device in a pixel interleaved arrangement can be adopted for the fifth embodiment, and the CCD solid-state imaging device in a tetragonal matrix can be adopted for the sixth embodiment.  
         [0124]    The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It is apparent that various modifications, improvements, combinations, and the like can be made by those skilled in the art.