Dark current suppression for solid state image sensing device

A solid-state image sensing device having a plurality of pixels each of which outputs to a transmission portion (12) a signal charge corresponding to an amount of light projected thereon. The signal charge transmitted by the transmission portion (12) is outputted as an image signal for each pixel from the solid state image sensing device. Each pixel includes a photo-diode (32), a storage portion (41) for storing charge corresponding to a current output from the photo-diode (32) onto which light is projected, a transfer portion (42) for transferring the charge stored by the storage portion to the transmission portion, and a control portion (39) for controlling an amount of charge to be received by the transmission portion based on a dark current characteristic of a corresponding photo-diode (32).

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention generally relates to a solid state image sensing 
device, and more particularly to a solid state image sensing device in 
which photo-electric charge generated in photo-diodes is stored therein 
and information corresponding to the photo-electric charge is read out 
therefrom by electronic scanning. 
In recent years, to increase the number of pixels in a solid state image 
sensing device and to arrange the pixels with a high density, it is 
required that all the pixels have uniform characteristics. Thus, 
improvements in the production process of the image sensing device have 
been attempted. On the other hand, it is difficult to obtain uniform 
characteristics of photo-diodes which are made, for example, of compound 
semiconductor. In this case, output signals from the solid state image 
sensing device are corrected by complex processing in an external circuit. 
In the solid state image sensing device field, it is desired that variation 
of output signals depending on dispersion of characteristics of the 
photo-diodes is reduced without complex processing in an external circuit. 
(2) Description of the Related Art 
In a conventional solid state image sensing device having photo-diodes, a 
single bias voltage is supplied to the respective photo-diodes and 
electric charge corresponding to the quantity of light to each photo-diode 
and affected by the dark current of each photo-diode is stored therein and 
read out therefrom. Thus, in an external circuit coupled to the solid 
state image sensing device, dark current characteristics of the respective 
photo-diodes have been previously stored in a semiconductor memory, and 
the output signal from each pixel is corrected based on a dark current 
characteristic stored in the semiconductor memory for a corresponding 
photo-diode. 
As has been described above, when the conventional solid state image 
sensing device is used, the dispersion of the dark currents of the 
respective photo-diodes must be compensated for by the external circuit. 
Thus, the external circuit coupled to the solid state image sensing device 
is complex and a long processing time is needed in the external circuit. 
In addition, if the bias voltage is set to a value suitable for a 
photo-diode having a small dark current, the storage capacity of electric 
charge in a photo-diode having a large dark current is insufficient so 
that an output signal from a corresponding pixel is saturated. In this 
case, this pixel is a defective pixel. On the other hand, if the bias 
voltage to be supplied to the photo-diodes is set to a low value to 
prevent pixels corresponding to photo-diodes having a large dark current 
from being defective, the sensitivity of the solid state image sensing 
device deteriorates. 
SUMMARY OF THE INVENTION 
Accordingly, a general object of the present invention is to provide a 
novel and useful solid state image sensing device in which the 
disadvantages of the aforementioned prior art are eliminated. 
A more specific object of the present invention is to provide a solid state 
image sensing device in which the dispersion of image signals caused by 
the dispersion of the characteristics, such as the dark currents, of 
photo-diodes can be reduced without processing in an external circuit. 
The above objects of the present invention are achieved by a solid state 
image sensing device having a plurality of pixels each of which outputs to 
a transmission portion signal electric charge corresponding to an amount 
of light projected thereon, the signal electric charge transmitted by said 
transmission portion being output as an image signal for each pixel from 
said solid state image sensing device, each pixel comprising: a 
photo-diode; storage means for storing electric charge corresponding to a 
current output from said photo-diode onto which a light is projected; 
transfer means for transferring the electric charge stored by said storage 
means to said transmission portion; and control means for controlling, in 
accordance with a characteristic of said photo-diode, an amount of signal 
electric charge to be received by said transmission portion. 
According to the present invention, since the amount of signal electric 
charge supplied from each pixel to the transmission portion is controlled 
in accordance with a characteristic of the photo-diode (e.g. the 
characteristic regarding the dark current or the sensitivity), a solid 
state image sensing device in which the dispersion of image signals caused 
by the dispersion of photo-diode characteristics, such as the dark 
currents, can be reduced without processing in an external circuit can be 
obtained. 
Additional objects, features and advantages will become apparent from the 
following detailed description when read in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description will now be given of embodiments of the present invention. 
FIG. 1 shows a CCD (Charge Coupled Device) type solid state image sensing 
device having pixels arranged in a 2.times.2 matrix. In FIG. 1, a 
photo-diode 32 and an input circuit having input gate electrodes 38 and 
39, a storage electrode 41 and a transfer gate electrode 42 are provided 
for each pixel. The input circuit is formed on an insulating layer on a 
substrate. In this input circuit, the dark current of the photo-diode 32 
corresponding to each pixel is controlled as will be described later. 
The electric charge generated by the photo-diode 32 on which light is 
incident is stored in the substrate under the storage electrode 41, and 
the electric charge for each pixel is transmitted (shifted) by a vertical 
CCD 12. When transistors 14 and 15 are turned on, the electric charge for 
pixels aligned in a row is transferred as pixel signals from the vertical 
CCDs 12 to a horizontal CCD 13. The horizontal CCD 13 transmits (shifts 
out) the pixel signals, and the pixel signals supplied from the horizontal 
CCD 13 to an amplifier 16 are output therefrom. 
FIG. 2 shows a MOS type solid state image sensing device having pixels 
arranged in a 2.times.2 matrix. In FIG. 2, the photo-diode 32 and the 
input circuit having the input gate electrodes 38 and 39, the storage 
electrode 41 and the transfer gate electrode 42 are provided for each 
pixel in the same manner as the case shown in FIG. 1. The transfer gate 
electrode 42 for each of pixels aligned in a row is selected and turned on 
by a vertical shift register 22. When transistors 24 and 25 are turned on, 
signals for the pixels aligned in the row are transferred to a horizontal 
CCD 23 via transfer gate electrodes 42. The horizontal CCD 23 transmits 
the signals for pixels aligned in each row, and the signals supplied from 
the horizontal CCD 13 to an amplifier 26 are output therefrom. 
In a first embodiment, the input circuit and the photo-diode 32 provided 
for each pixel are formed as shown in FIGS. 3, 4 and 5. 
Referring to FIG. 3, an n-type region 36 is formed near the surface of the 
p-type substrate 33 therein, and an insulating film 34 is formed on the 
surface of the p-type substrate 33 so as to overlap with the n-type region 
36. The n-type region 36, the p-type substrate 33, the insulating film 34 
and the electrode 37 form an input diode. The n-type region 36 is 
connected to the cathode of the photo-diode 32 corresponding to a pixel 
via an electrode 37. The anode of the photo-diode 32 is grounded. The 
photo-diode 32 is sensitive, for example, to infrared rays. 
The substrate 33 is covered by an insulating film 35 made of SiO.sub.2. The 
input gate electrode 38, the storage electrode 41, the transfer gate 
electrode 42 and a transmission portion electrode 43 of the vertical CCD 
12 are formed on the insulating film 35. The input gate electrode 39 which 
is used to control a bias voltage of the photo-diode 32 is also formed on 
the insulating film 35. A floating electrode 40 is formed in the 
insulating film 35 under the input gate electrode 39. The floating 
electrode 40 functions to control the bias voltage to be supplied to the 
photo-diode 32. The substrate 33 is grounded. 
In the first embodiment, electrons are injected into the floating electrode 
40 in accordance with the size of the dark current of the photo-diode 32, 
and the electrons are maintained in the floating electrode 40. The bias 
voltage supplied to the photo-diode 32 is controlled by the electrons 
maintained in the floating electrode 40, so that the dark current of the 
photo-diode 32 is corrected. 
The details are as follows. 
First, under a condition in which no light is incident on the photo-diode 
32, electrons corresponding to the dark current of the photo-diode 32 is 
stored in a potential well 51 formed in the substrate 33 under the input 
gate electrode 39. The potential well 51 is formed as follows. The input 
gate electrode 38 is controlled so as to be maintained, for example, at 
about 1 volt which corresponds to the bias voltage of the photo-diode 32, 
so that an input gate is opened. Further, the input gate electrode 39 is 
maintained at a predetermined voltage which is about 10 volts, so that the 
potential well 51 is formed under the input gate electrode 38. 
In order to prevent the leakage of electrons stored in the potential well 
51, a low voltage is supplied to the storage electrode 41, and the 
transfer gate electrode 42 is maintained at 0 volt so that the transfer 
gate is shut down. 
In the above state, electrons are injected into the potential well 51 by 
the dark current of the photo-diode 32 for a predetermined time. 
After this, as shown in FIG. 4, the input gate electrode 38 is controlled 
so as to be maintained at 0 volt so that the input gate is shut down, and 
the input gate electrode 39 is maintained at a voltage which is about 50 
volts higher than the previous voltage. As a result, the electrons stored 
in the potential well 51 are injected into the floating electrode 40. 
FIG. 6 is a potential diagram indicating the potential in a section taken 
along a line X1-X2 shown in FIG. 4. In FIG. 6, the electrons stored in the 
potential well 51 formed in the substrate 33 tunnel through an insulating 
portion 45 under the floating electrode 40 and are injected into the 
floating electrode 40. The electrons are then stored in the floating 
electrode 40. In this case, the electric charge of the electrons injected 
into the floating electrode 40 is in proportion to the number of electrons 
stored in the potential well 51 by the dark current of the photo-diode 32. 
To inject the electrons into the floating electrode 40, light having energy 
exceeding the energy barrier of the insulating portion 45 may also be 
projected onto the surface of the input circuit under a condition in which 
the electric charge corresponding to the dark current of the photo-diode 
32 is stored in the potential well 51. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is injected into the floating electrode 40 as described 
above, light is incident on the photo-diode 32 in an imaging operation. 
FIG. 5 shows a state where signal electric charge is stored in a potential 
well 52 formed in the substrate 33 under the storage electrode 41 in the 
imaging operation. The storage electrode 41 is maintained at a voltage of 
about 10 volts, so that the potential well 52 is formed. 
In the imaging operation, the bias voltage supplied to the photo-diode 32 
is controlled by the input gate electrode 39. A predetermined voltage is 
supplied to the input gate electrode 39 and a voltage slightly higher than 
the predetermined voltage supplied to the input gate electrode 39 is 
supplied to the input gate electrode 38. In the imaging operation, the 
operating point of the photo-diode 32 is moved in accordance with the 
amount of electric charge maintained in the floating electrode 40, so that 
the signal electric charge obtained based on the correction of the 
dispersion of the dark currents of the photo-diodes in the solid state 
image sensing device is stored in the potential well 52. 
The dispersion of the dark currents of the photo-diodes in the solid state 
image sensing device is reduced in the imaging operation as follows. 
FIG. 7A shows a current-voltage characteristic of the photo-diode 32. The 
photo-diode 32 operates under a condition in which a bias voltage is 
supplied as a reverse bias thereto. A current Ib.sub.0 at the operating 
point a.sub.0 at which a predetermined bias voltage V.sub.po is supplied 
to the photo-diode 32 without light incident on the photo-diode 32 is the 
dark current. 
FIG. 7B shows a drain current-gate voltage (I.sub.D -V.sub.G characteristic 
of a virtual transistor having as virtual source the n-type region 36, as 
virtual drain of the storage electrode 41 and as virtual gate the input 
gate electrode 39. The virtual transistor has a threshold voltage 
V.sub.th. 
In the input circuit, the photo-diode 32 and the virtual transistor are 
serially connected to each other, and the operating point of the 
photo-diode 32 depends on the current-voltage characteristic of the 
photo-diode 32 and the I.sub.D -V.sub.G characteristic of the virtual 
transistor. 
The operating point of the photo-diode 32 is moved by shifting the 
threshold voltage V.sub.th of the virtual transistor as shown in FIG. 8. 
In FIG. 8, P.sub.F1 represents a characteristic of a photo-diode PV1 
having a small dark current, and P.sub.F2 represents a characteristic of a 
photo-diode PV2 having a large dark current. A continuous line T.sub.FO 
represents an initial drain current-gate voltage characteristic of the 
virtual transistor. The dark current of the photo-diode PV1 is Ib1 at an 
operating point a1. The dark current of the photo-diode PV2 is Ib2 at an 
operating point a2. The dark current Ib2 of the photo-diode PV2 is about 
two and a half times as large as the dark current Ib1 of the photo-diode 
PV1. 
When the electric charge Q corresponding to the dark current is injected 
into the floating electrode 40, the threshold voltage V.sub.th is shifted. 
The shifting quantity .DELTA.V.sub.th of the threshold voltage V.sub.th is 
represented by 
EQU .DELTA.V.sub.th =-Q/(.epsilon..sub.2 /d.sub.2) 
where d.sub.2 is the thickness of an insulating portion 44 as shown in FIG. 
6, the insulating portion 44 lying between the input gate electrode 39 and 
the floating electrode 40 as shown in FIG. 4, .epsilon..sub.2 is the 
dielectric constant of the insulating portion 44. 
Thus, in the input circuit connected to the photo-diode having a large dark 
current, the threshold voltage V.sub.th of the virtual transistor is 
greatly shifted. In FIG. 8, in the input circuit connected to the 
photo-diode PV1, the threshold voltage V.sub.th of the virtual transistor 
is shifted by .DELTA.V.sub.th1, and in the input circuit connected to the 
photo-diode PV1, the threshold voltage V.sub.th is shifted by 
.DELTA.V.sub.th2. The shifting quantity .DELTA.V.sub.th2 of the 
photo-diode PV2 is about two and a half times as large as the shifting 
quantity .DELTA.V.sub.th1 of the photo-diode PV1. 
Due to the shifting of the threshold voltage V.sub.th of the virtual 
transistor, the operating point of the photo-diode PV1 is moved from a1 to 
a2, and the operating point of the photo-diode PV2 is moved from b1 to b2. 
Due to moving of the operating point, the dark current of the photo-diode 
PV1 is changed from Ib1 to Ib1.sub.s which is approximately equal to Ib1. 
That is, the dark current of the photo-diode PV1 is almost unchanged. On 
the other hand, the dark current of the photo-diode PV2 is greatly 
decreased from Ib2 to Ib2.sub.s. 
As has been described above, the larger the dark current of the 
photo-diode, the further the operating point of the photo-diode is moved 
towards the lower voltage of the reverse bias of the photo-diode. As a 
result, a larger the dark current of the photo-diode, the larger the 
quantity by which the dark current is decreased by the electric charge 
injected into the floating electrode 40. Thus, the dispersion of dark 
currents of photo-diodes in the solid state image sensing device can be 
reduced. In addition, since the dark current of the photo-diode is 
controlled by controlling the bias voltage thereof, the defective pixels 
and deterioration of sensitivity, which are caused by the lack of the 
storage capacity of electric charge in a portion under the storage 
electrode 41 do not occur. 
The dispersion of the dark currents of the photo-diodes is reduced as has 
been described above, and signal electric charge corresponding to each of 
the dark currents whose dispersion is reduced is stored in the potential 
well 52 located under storage electrode 41 provided for each pixel, in the 
imaging operation shown in FIG. 5. 
After the signal electric charge is completely stored in the potential well 
52, voltages which are higher than the voltage supplied to the storage 
electrode 41 are supplied to the transfer gate electrode 42 and the 
transmission portion electrode 43. As a result, the signal electric charge 
is transferred from the potential well 52 to a transmission portion in the 
substrate under the transmission portion electrode 43. After this, the 
transfer gate electrode 42 is set to 0 volt so that the transfer gate is 
shut down, and the electric charge in the transmission portion is 
transmitted (shifted) in a direction perpendicular to the plane of the 
drawing of FIG. 5. Due to the transmission of the signal electric charge, 
the solid state image sensing device outputs signals. 
FIG. 9A shows output signals of the solid state image sensing device in a 
case where no electric charge corresponding to the dark current is stored 
in the floating electrode 40. The output signals include the dispersion of 
the dark currents of the respective photo-diodes PV1, PV2, PV3, PV4, . . . 
. On the other hand, FIG. 9B shows output signals of the solid state image 
sensing device in a case where electric charge corresponding to the dark 
current is stored in the floating electrode 40. In this case, the 
dispersion of the dark currents of the photo-diodes PV1, PV2, PV3, PV4, . 
. . is reduced. Thus, it is not necessary for the external circuit to 
correct the dispersion of the output signals. As a result, the external 
circuit can be simplified in comparison with an external circuit coupled 
to the conventional solid state image sensing device. 
Since the floating electrode 40 is insulated from other electrodes, the 
electric charge injected into the floating electrode 40 is maintained 
therein even if the power supply to the solid state image sensing device 
is turned off. Thus, the function in which the dispersion of the dark 
currents of the photo-diodes is reduced, once performed, can remain in 
effect in the solid state image sensing device for a long time. 
The injection of the electric charge into the floating electrode 40 can be 
repeated. In this case, under a condition in which a negative voltage is 
supplied as the reverse bias to the input gate electrode 39, a negative 
voltage whose absolute value is greater than that of the above negative 
voltage is supplied to the input gate electrode 39, or under a reverse 
biasing condition, ultraviolet rays are projected onto the device. In this 
way, the electric charge stored in the floating electrode 40 is set free 
and dispersed in the substrate 33. After this, new electric charge is 
injected into the floating electrode 40. 
In the above embodiment, under a condition in which no light is incident on 
the photo-diode 32, the electric charge corresponding to the dark current 
is stored in the potential well 51 located under the input gate electrode 
39, and an amount of electric charge corresponding to the amount of 
electric charge stored in the potential well 51 is injected into the 
floating electrode 40. However, the electric charge can be also injected 
into the floating electrode 40 as follows. 
Under a condition in which light is uniformly projected onto the 
photo-diode 32 so that a current slightly greater than the dark current is 
generated by the photo-diode 32, the electric charge is stored in the 
potential well 51, and the amount of electric charge corresponding to the 
amount of electric charge stored in the potential well 51 is injected into 
the floating electrode 40. In this case, the amount of electric charge 
injected into the floating electrode 40 is increased by the projection of 
the light onto the photo-diode 32. Thus, in the imaging operation, a 
voltage supplied to the input gate electrode 39 is controlled so as to be 
increased by the amount corresponding to the increasing of the electric 
charge injected in the floating electrode 40. As a result, the dispersion 
of the dark currents of the photo-diodes can be reduced in the same manner 
as in a case where the electric charge is stored in the potential well 51 
under a condition in which no light is incident on the photo-diodes. 
In this solid state image sensing device, the dispersion of levels of the 
output signals caused by the dispersion of sensitivities of the 
photo-diodes can be reduced in the same manner as for the dispersion of 
the dark currents described above. First, an amount of electric charge 
corresponding to the sensitivity of each photo-diode 32 is stored in the 
potential well 51 under a condition in which a weak light is projected 
onto each of the photo-diodes 32. Next, an amount of electric charge 
corresponding to the amount of electric charge stored in the potential 
well 51 is injected into the floating electrode 40. In this case, the 
higher the sensitivity of the photo-diode, the larger the amount of 
electric charge injected into the floating electrode. In the imaging 
operation, the bias voltage across each photo-diode is corrected in 
accordance with the amount of electric charge injected into the floating 
electrode 40 so that the dispersion of the levels of the output signals 
caused by the dispersion of the sensitivities of the respective 
photo-diodes is reduced. 
After the electric charge corresponding to the dark current is stored in 
the potential well 52 located under the storage electrode 41, the electric 
charge may be injected into the floating electrode 40. 
A description will now be given, with reference to FIGS. 10 and 11, of a 
second embodiment of the present invention. In FIG. 10, those parts which 
are the same as those shown in FIG. 3 are given the same reference 
numbers. 
In each input circuit of the solid state image sensing device according to 
the second embodiment shown in FIG. 10, a multilayer insulating film 
including an insulating layer 46 made of Si.sub.3 N.sub.4 and an 
insulating layer 47 made of SiO.sub.2 is formed under the input gate 39 
used to supply the bias voltage to the photo-diode 32. In this input 
circuit, after electric charge corresponding to the dark current of the 
photo-diode 32 is stored in the potential well 51, the electric charge is 
injected into a boundary portion between the insulating layers 46 and 47 
and the insulating layer 46 itself and trapped therein. 
FIG. 11 shows a potential in a section taken along a line X3-X4 shown in 
FIG. 10. As shown in FIG. 11, electrons stored in the potential well 51 in 
the substrate 33 tunnel through the insulating layer 47 and are injected 
into a charge trapping portion in the boundary between the insulating 
layers 46 and 47 and the insulating layer 46 itself. The electrons are 
trapped in the charge trapping portion. The electric charge of the 
electrons injected into the charge trapping portion is in proportion to 
the number of electrons stored in the potential well 51, the number of 
electrons corresponding to the dark current of the photo-diode 32. The 
operating point of the photo-diode 32 is moved, in the same manner as that 
described in the first embodiment, in accordance with the amount of 
electric charge injected into the charge trapping portion in the boundary 
between the insulating layer 46 and 47 and the insulating layer 46 itself. 
Thus, in the second embodiment, due to the action of the electric charge 
stored in the multilayer insulating film including the insulating layers 
46 and 47, which electric charge corresponds to the dark current of 
photo-diode 32 in each pixel, in the imaging operation, the dispersion of 
the dark currents can be reduced in the same manner as in the first 
embodiment. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is stored in the potential well located under the storage 
electrode 41, the electric charge may be injected into the charge trapping 
portion in the insulating layers 46 and 47. 
A description will now be given, with reference to FIGS. 12, 13 and 14, of 
a third embodiment of the present invention. In FIGS. 12, 13 and 14, those 
parts which are the same as those shown in FIG. 3 are given the same 
reference numbers. 
Referring to FIGS. 12, 13 and 14, an input gate electrode 61, the storage 
electrode 41, the transfer gate electrode 42 and the transmission portion 
electrode 43 of the vertical CCD 12 are stacked on a structure including 
the substrate 33 and the insulating film 35 so as to be separated from the 
substrate 33 by the insulating film 35. The input gate electrode 61 is 
used to control the bias voltage of the photo-diode 32. A floating 
electrode 62 is formed in the insulating film 35 under the input gate 61. 
The floating gate 62 has the function of correcting the bias voltage of 
the photo-diode 32. The substrate 33 is grounded. 
In the third embodiment, electrons corresponding to the dark current of the 
photo-diode 32 are injected into and stored in the floating electrode 62, 
and the dark current of the photo-diode 32 is corrected using the electric 
charge of the electrons stored in the floating electrode 62. The details 
will be described below. 
First, under a condition in which no light is incident on the photo-diode 
32, as shown in FIG. 12, the voltage supplied to the input gate electrode 
61 is controlled so as to be maintained, for example, at 1 volt so as to 
correspond to the bias voltage of the photo-diode 32, so that an input 
gate is opened. In addition, the storage electrode 41 is maintained at a 
predetermined voltage of about 10 volts so that a potential well 65 is 
formed under the storage electrode 41. The transfer gate electrode 42 is 
maintained at 0 volts, so that the transfer gate is shut down. In this 
state, electrons corresponding to the dark current of the photo-diode 32 
are injected into the potential well 65 for a predetermined time. 
After this, as shown in FIG. 13, a high voltage of about 50 volts is 
supplied to the input gate electrode 61, so that the electrons stored in 
the potential well 65 are injected into the floating electrode 62. The 
electric charge Q of the electrons injected into the floating electrode 65 
is in proportion to the number of electrons, corresponding to the dark 
current of the photo-diode 32, which are stored in the potential well 65. 
If the voltage-proof of the photo-diode 32 is low, the anode of the 
photo-diode 32 is disconnected from the ground line while the electric 
charge is being injected into the floating electrode. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is injected into the floating electrode 62 as described 
above, the imaging operation is carried out under a condition in which 
light is projected onto the photo-diode 32. FIG. 14 shows a state where 
signal electric charge is stored in a potential well 66 formed under the 
storage electrode 41 in the imaging operation. A voltage of about 10 volts 
is supplied to the storage electrode 41, so that the potential well 66 is 
formed under the storage electrode 41. 
In the imaging operation, the bias voltage of the photo-diode 32 is 
controlled using the input gate electrode 61. At this time, the operating 
point of the photo-diode 32 is moved, in the same manner as in the first 
embodiment, in accordance with the electric charge injected into the 
floating electrode 62, so that the bias voltage of the photo-diode 32 is 
varied. Thus, the dispersion of the dark currents of the respective 
photo-diodes in the solid state image sensing device is reduced, and 
signal electric charge including a component corresponding to a dark 
current is stored in the potential well 66 for each pixel. 
According to the third embodiment, the dispersion of the dark currents of 
the photo-diodes in the solid state image sensing device is reduced, in 
the imaging operation, by the electric charge corresponding to each of the 
dark currents, stored in the floating electrode 62. 
A description will now be given, with reference to FIG. 15, of a fourth 
embodiment of the present invention. In FIG. 15, those parts which are the 
same as those shown in FIG. 12 are given the same reference numbers. 
In each input circuit of the solid state image sensing device according to 
the fourth embodiment shown in FIG. 15, a multilayer insulating film 
including an insulating layer 63 made of Si.sub.3 N.sub.4 and an 
insulating layer 64 made of SiO.sub.2 is formed under the input gate 61 
used to supply the bias voltage to the photo-diode 32. In this input 
circuit, after electric charge corresponding to the dark current of the 
photo-diode 32 is stored in the potential well 65, the electric charge is 
injected into a boundary portion between the insulating layers 63 and 64 
and the insulating layer 46 itself and trapped therein. The electric 
charge of the electrons injected into a charge trapping portion in the 
multilayer insulating film is in proportion to the number of electrons, 
corresponding to the dark current of the photo-diode 32, stored in the 
potential well 65. 
The operating point of the photo-diode 32 is moved, in the same manner as 
in the third embodiment, in accordance with the amount of electric charge 
injected into the charge trapping portion in the boundary between the 
insulating layers 63 and 64 and the insulating layer 63 itself. Thus, the 
dispersion of the dark currents of the photo-diodes in the solid state 
image sensing device can be reduced, in the same manner as in the third 
embodiment, by the electric charge trapped in the multilayer insulating 
film including the insulating layers 63 and 64 for each pixel, in the 
imaging operation. 
A description will now be given, with reference to FIGS. 16, 17, 18 and 19, 
of a fifth embodiment of the present invention. In FIGS. 16, 17, 18 and 
19, those parts which are the same as those shown in FIG. 3 are given the 
same reference numbers. 
Referring to FIGS. 16, 17, 18 and 19, an input gate electrode 38, the 
storage electrode 41, a transfer gate electrode 71 and the transmission 
portion electrode 43 of the vertical CCD 12 are stacked on a structure 
including the substrate 33 and the insulating film 35 so as to be 
separated from the substrate 33 by the insulating film 35. The input gate 
electrode 38 is used to control the bias voltage of the photo-diode 32. A 
floating electrode 72 is formed in the insulating film 35 under the 
transfer gate electrode 71. The floating gate 72 has a function for 
correcting the amount of signal electric charge to be supplied to the 
transmission portion in accordance with the characteristic of the 
photo-diode 32. The substrate 33 is grounded. 
In the fifth embodiment, electrons corresponding to the dark current of the 
photo-diode 32 are injected into and stored in the floating electrode 72, 
and the amount of the signal electric charge to be transmitted to the 
transmission portion of the vertical CCD 12 is corrected using the 
electric charge of the electrons stored in the floating electrode 72. The 
details will be described below. 
First, under a condition in which no light is incident on the photo-diode, 
as shown in FIG. 16, a voltage supplied to the input gate electrode 38 is 
controlled so as to be maintained, for example, at 1 volt so as to 
correspond to the bias voltage of the photo-diode 32, so that the input 
gate is opened. In addition, a voltage of about 10 volts is supplied to 
the transfer gate electrode 71, so that a potential well 75 is formed 
under the transfer gate electrode 71. A voltage of 0 volts is supplied to 
the transmission portion electrode 43, so that the transfer gate is shut 
down. In the above state, electrons corresponding to the dark current of 
the photo-diode 32 are stored in the potential well 75 for a predetermined 
time. 
Subsequently, as shown in FIG. 17, in a state where a voltage of 0 volts is 
supplied to the input gate electrode 38 so that the input gate is shut 
down, a high voltage of about 50 volts is supplied to the transfer gate 
electrode 71, so that the electrons stored in the potential well 75 are 
injected into the floating electrode 72. The electric charge of the 
electrons injected into the floating electrode 72 is in proportion to the 
number of electrons, corresponding to the dark current of the photo-diode 
32, stored in the potential well 75. 
After the electric charge corresponding to the dark current is stored in 
the floating electrode 72 as has been described above, the light is 
projected onto the photo-diode 32 and the imaging operation is carried 
out. FIGS. 18 and 19 show states where the transmission of signal electric 
charge is performed in the imaging operation. 
In the imaging operation, due to voltage control of the input gate 
electrode 38, the bias voltage of the photo-diode 32 is controlled at a 
predetermined value. A voltage of about 10 volts is supplied to the 
storage electrode 41 and a voltage of 0 volts is supplied to the transfer 
gate electrode 71 so that the transfer gate is shut down. As a result, the 
signal electric charge is stored in a potential well 76 located under the 
storage electrode 41 as shown in FIG. 18. 
After the signal electric charge is stored in the potential well 76, a 
voltage supplied to the transfer gate electrode 71 is controlled at a 
predetermined value which is approximately equal to that of the voltage 
supplied to the storage electrode 41 so that the transfer gate is opened. 
The voltage supplied to the transmission portion electrode 43 is then 
controlled so as to be higher than the voltage supplied to the transfer 
gate electrode 71. At this time, if the dark current of the photo-diode is 
equal to zero, the potential of a portion under the transfer gate 
electrode 71 is equal to the potential of the bottom of the potential well 
76 located under the storage electrode 41. As a result, the entire signal 
electric charge stored in the potential well 76 is transferred to the 
transmission portion via the transmission gate. 
Since the actual dark current of the photo-diode 32 is not equal to zero, 
the electric charge corresponding to the value of the dark current is 
injected into the floating electrode 72. Thus, the potential barrier is 
elevated by the quantity corresponding to the amount of electric charge 
injected into the floating electrode 72. As a result, the electric charge 
corresponding to the dark current of the photo-diode 32 remains in the 
potential well 76 located under the storage electrode 41, and the signal 
electric charge corresponding to only the amount of light projected onto 
the photo-diode 32 is transferred to the transmission portion of the 
vertical CCD 12 via the transmission gate. 
FIG. 18 shows a case where a small dark current is generated by the 
photo-diode 32. In this case, only a small amount of electric charge is 
injected into the floating electrode 72, so that the potential barrier of 
the portion located under the transfer gate electrode 71 is low. Thus, a 
small amount of electric charge corresponding to the dark current remains 
in the potential well 76 located under the storage electrode 41. 
On the other hand, FIG. 19 shows a case where a large dark current is 
generated by the photo-diode 32. In this case, a large amount of electric 
charge is injected into the floating electrode 72, so that the potential 
barrier of the portion located under the transfer gate electrode 71 is 
high. Thus, a large amount of electric charge corresponding to the dark 
current of the photo-diode 32 remains in the potential well 76 located 
under the storage electrode 41. 
FIG. 20 shows a state where the electrons remaining in the potential well 
76 move. That is, after the transferring of the signal electric charge is 
completed, the electrons remaining in the potential well 76 passes, as 
shown by an arrow ml in FIG. 20, thorough an ejecting gate located under 
an ejecting gate electrode 79 and are ejected from an ejecting drain 
electrode 78. 
As has been described above, according to the fifth embodiment, due to the 
operation of the floating electrode 72 in which the electric charge 
corresponding to the dark current of the photo-diode 32 is stored, the 
signal electric charge to which the correction regarding the dark current 
is applied can be transferred to the transmission portion in the imaging 
operation. Thus, the solid state image sensing device can generate output 
signals to which the correction regarding the dark currents is applied. In 
addition, it is prevented that each stage in the transmission portion is 
saturated with the electric charge by the dark current and the electric 
charge further overflows into the next stage. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is stored in the potential well formed under the storage 
electrode 41, this electric charge may be injected into the floating 
electrode 72. 
A description will now be given, with reference to FIG. 21, of a sixth 
embodiment of the present invention. In FIG. 21, those parts which are the 
same as those shown in FIG. 16 are given the same reference numbers. In 
the sixth embodiment shown in FIG. 21, a multilayer insulating film having 
an insulating layer 73 made of Si.sub.3 N.sub.4 and an insulating layer 74 
made of SiO.sub.2 is formed under the transfer gate electrode 71. 
In the sixth embodiment, after the electric charge corresponding to the 
dark current of the photo-diode 32 is stored in the potential well 75, the 
electric charge is injected into a charge trapping portion in the boundary 
between the insulating layers 73 and 74 and the insulating layer 73 itself 
and maintained therein. The amount of the electric charge injected into 
the charge trapping portion is in proportion to the number of electrons, 
corresponding to the dark current of the photo-diode 32, stored in the 
potential well 75. 
The height of the potential barrier of the transfer gate in the imaging 
operation is controlled, in the same manner as in the fifth embodiment, in 
accordance with the amount of electric charge injected into the charge 
trapping portion in the boundary between the insulating layers 73 and 74 
and the insulating layer 73 itself. Thus, due to the operation of the 
multilayer insulating film having the insulating layers 73 and 74 in which 
the electric charge corresponding to the dark current is injected, the 
signal electric charge to which the correction regarding the dark current 
is applied can be transferred to the transmission portion, in the same 
manner as in the fifth embodiment. 
A description will now be given, with reference to FIGS. 22, 23 and 24, of 
a seventh embodiment of the present invention. In FIGS. 22, 23 and 24, 
those parts which are the same as those shown in FIG. 16 are given the 
same reference numbers. 
Referring to FIGS. 22, 23 and 24, a skimming gate electrode 81 is provided 
between the storage electrode 41 and the transfer gate electrode 42. A 
floating electrode 82 is formed in the insulating layer 35 under the 
skimming gate electrode 81. The floating gate 82 is used to control the 
amount of the signal electric charge to be output in accordance with the 
characteristic of the photo-diode 32. The substrate is grounded. 
In the seventh embodiment, electrons corresponding to the dark current of 
the photo-diode 32 are injected into and maintained in the floating 
electrode 82, and the amount of signal electric charge transferred to the 
transmission portion of the vertical CCD 12 is controlled by the electric 
charge stored in the floating electrode. The details will be described 
bellow. 
First, as shown in FIG. 22, a voltage supplied to the input gate electrode 
38 is controlled so as to correspond to the bias voltage of the 
photo-diode 32, so that the input gate is opened. The storage electrode 41 
is maintained at a voltage approximately equal to the voltage supplied to 
the input gate electrode 38. The skimming gate electrode is controlled so 
as to be maintained at a predetermined voltage of about 10 volts so that a 
potential well 85 is formed under the skimming gate electrode 81. The 
transfer gate electrode 42 is maintained at 0 volts so that the transfer 
gate is shut down. In the above state, electrons corresponding to the dark 
current of the photo-diode 32 are stored in the potential well 85 for a 
predetermined time. 
Subsequently, as shown in FIG. 23, in a state where the input gate 
electrode 38 is maintained at 0 volts so that the input gate is shut down, 
a high voltage of about 50 volts is supplied to the skimming gate 
electrode 81, so that the electrons stored in the potential well 85 are 
injected into the floating electrode 82. The electric charge injected into 
the floating electrode 82 is in proportion to the number of electrons, 
corresponding to the dark current of the photo-diode 32, stored in the 
potential well 85. 
After the electric charge is stored in the floating electrode 82 as 
described above, light is projected onto the photo-diode 32 and the 
imaging operation is performed. FIG. 24 shows the structure of each pixel 
in the solid state image sensing device in the imaging operation. 
In the imaging operation, the bias voltage of the photo-diode 32 is 
controlled so as to be maintained at a predetermined value using the input 
gate electrode 38. A predetermined voltage of about 10 volts is supplied 
to the storage electrode 41, and the transfer gate electrode 42 is 
provided with 0 volts so that the transfer gate is shut down. As a result, 
the signal electric charge is stored in the potential well 86 located 
under the storage electrode 41. 
After the signal electric charge is completely stored in the potential well 
86, the voltage of the skimming gate electrode 81 in each input circuit is 
controlled so as to be maintained at a predetermined value slightly less 
than that of the voltage supplied to the storage electrode 41, so that the 
skimming gate is opened. In addition, the transfer gate electrode 42 and 
the transmission portion electrode 43 are provided with voltages each of 
which is greater than the voltage supplied to the skimming gate electrode 
81. At this time, the electric charge corresponding to the dark current 
has been injected into the floating electrode 82, so that the potential 
barrier of a portion located under the skimming gate electrode 81 is 
elevated by the quantity corresponding to the electric charge injected 
into the floating electrode 82. Thus, the electric charge corresponding to 
the dark current of the photo-diode 32 remains in the potential well 86 
located under the storage electrode 41 and the signal electric charge 
corresponding to only the amount of light incident on the photo-diode 32 
is transferred to the transmission portion of the vertical CCD 12 via the 
transmission gate. The electric charge which remains in the potential well 
86 is ejected, in the same manner as in the sixth embodiment, via the 
ejecting drain electrode after the transferring of the electric charge is 
completed. 
As has been described above, according to the seventh embodiment, due to 
the operation of the floating electrode 82 in which the electric charge 
corresponding to the dark current of the photo-diode 32 is stored, the 
signal electric charge to which the correction regarding the dark current 
of the photo-diode 32 is applied can be transferred to the transmission 
portion in the imaging operation. In addition, since the skimming gate 
electrode can be controlled to be maintained at a constant voltage, noise 
hardly affects the solid state image sensing device in comparison with the 
case of the fifth embodiment in which the electric charge corresponding to 
the dark current is stored in the portion located under the transfer gate 
electrode 42. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is stored in the potential well located under the storage 
electrode 41, the electric charge may be injected into the floating 
electrode 82. 
A description will now be given, with reference to FIG. 25, of an eighth 
embodiment of the present invention. In FIG. 25, those parts which are the 
same as those shown in FIG. 22 are given the same reference numbers. 
Referring to FIG. 25, a multilayer insulating film having an insulating 
layer 83 made of Si.sub.3 N.sub.4 and an insulating layer 84 made of 
SiO.sub.2 is formed under the skimming gate electrode 81. In the eighth 
embodiment, after the electric charge corresponding to the dark current of 
the photo-diode 32 is stored in the potential well 85, the electric charge 
is injected into and maintained in the charge trapping portion in the 
boundary between the insulating layers 83 and 84 and the insulating layer 
83 itself. The amount of the electric charge injected into the charge 
trapping portion is in proportion to the number of electrons, 
corresponding to the dark current of the photo-diode 32, stored in the 
potential well 85. 
The height of the potential barrier of the skimming gate in the imaging 
operation is controlled, in the same manner as in the seventh embodiment, 
in accordance with the amount of electric charge injected into the charge 
trapping portion in the boundary between the insulating layers 83 and 84 
and the insulating layer 83 itself. Thus, due to the insulating layers 83 
and 84 in which the electric charge corresponding to the dark current is 
stored, the signal electric charge to which the correction regarding the 
dark current of the photo-diode 32 is applied can be transferred to the 
transmission portion in the imaging operation, in the same manner as in 
the seventh embodiment. 
A description will now be given, with reference to FIGS. 26, 27, 28 and 29, 
of a ninth embodiment of the present invention. In FIGS. 26, 27 and 28, 
those parts which are the same those shown in FIG. 22 are given the same 
reference numbers. 
Referring to FIGS. 26, 27 and 28, a skimming gate electrode 93 is provided 
between storage electrodes 91 and 92 so that the storage electrodes 91 and 
92 are separated from each other. A floating electrode 94 is formed in the 
insulating film 35 under the skimming gate electrode 93. The floating 
electrode 94 is used to control the amount of output signal electric 
charge in accordance with the characteristic of the photo-electrode 32. 
The substrate 33 is grounded. 
In the ninth embodiment, electrons corresponding to the dark current of the 
photo-diode 32 are injected into and stored in the floating electrode 93, 
and due to the electric charge of the electrons stored in the floating 
electrode 93, the amount of signal electric charge transferred to the 
transmission portion of the vertical CCD 12 is controlled. The details 
will be described below. 
First, as shown in FIG. 26, the voltage supplied to the input gate 
electrode 38 is controlled so as to correspond to the bias voltage of the 
photo-diode 32, so that the input gate is opened. The storage electrode 91 
is maintained at a voltage approximately equal to the voltage supplied to 
the input gate electrode 38. The skimming gate electrode 93 is maintained 
at a predetermined voltage of about 10 volts so that a potential well 97 
is formed under the skimming electrode 93. The transfer gate electrode 42 
is maintained at 0 volts so that the transfer gate is shut down. In the 
above state, electrons corresponding to the dark current of the 
photo-diode 32 are injected into the potential well 97 for a predetermined 
time. 
After this, as shown in FIG. 27, in a state where the input gate electrode 
is controlled so as to be maintained at 0 volt so that the input gate is 
shut down, the skimming gate 93 is maintained at a high voltage of about 
50 volts, and the electrons stored in the potential well 97 are injected 
into the floating electrode 94. The quantity of electric charge of the 
electrons injected into the floating electrode 94 is in proportion to the 
number of electrons, corresponding to the dark current of the photo-diode 
32, stored in the potential well 97. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is injected into the floating electrode 94 as described 
above, light is projected onto the photo-diode 32; and the imaging 
operation is carried out. FIG. 28 shows a state of the solid state image 
sensing device in the imaging operation. 
In the image operation, the voltage of the input gate electrode 38 is 
controlled so that the bias voltage of the photo-diode 32 is maintained at 
a predetermined value. A voltage of about 10 volts is supplied to the 
storage electrodes 91 and 92. The skimming gate electrode 93 is provided 
with a voltage which is less than the voltage of the storage electrode 91 
by a predetermined value. The transfer gate electrode is maintained at 0 
volts so that the transfer gate is shut down. In the above state, the 
signal electric charge is stored in a potential well 98 located under the 
storage electrode 91 and a potential well 100 located under the storage 
electrode 92. 
After the signal electric charge is completely stored in the potential 
wells 98 and 100, the transfer gate electrode 42 is controlled so as to be 
maintained at a voltage greater than the voltage of the storage electrode 
92 so that the transfer gate is opened. At this time, the electric charge 
corresponding to the dark current of the photo-diode 32 has been injected 
into the floating electrode 94, so that the potential barrier 99 of a 
portion under the skimming gate electrode 93 is elevated by the quantity 
corresponding to the amount of electric charge injected into the floating 
electrode 94. Thus, the electric charge corresponding to the dark current 
of the photo-diode 32 remains in the potential well 98 located under the 
storage electrode 91, and the signal electric charge corresponding to only 
the amount of light incident to the photo-diode is transferred from the 
potential well 100 located under the storage electrode 92 to the 
transmission portion of the vertical CCD 12 via the transmission gate. 
FIG. 29 shows a state where the electric charge remaining in the potential 
well 98 moves. That is, after the transferring of the signal electric 
charge is completed, the electric charge which remains in the potential 
well 76 passes, as shown by an arrow m2 in FIG. 29, thorough an ejecting 
gate located under an ejecting gate electrode 79 and is ejected from an 
ejecting drain electrode 78. 
As described above, according to the ninth embodiment, due to the floating 
electrode 94 in which the electric charge corresponding to the dark 
current of the photo-diode 32 is stored, the signal electric charge to 
which the correction regarding the dark current of the photo-diode is 
applied can be transferred to the transmission portion in the imaging 
operation. 
After the electric charge corresponding to the dark current of the 
photo-diode 32 is stored in the potential well formed under the storage 
electrode 91, this electric charge may be injected into the floating 
electrode 94. 
A description will now be given, with reference to FIG. 30, of a tenth 
embodiment of the present invention. In FIG. 30, those parts which are the 
same as those shown in FIG. 26 are given the same reference numbers. 
Referring to FIG. 30, a multilayer insulating film having an insulating 
layer 95 made of Si.sub.3 N.sub.4 and an insulating layer 96 made of 
SiO.sub.2 is formed under the skimming gate electrode 93. 
In the tenth embodiment, after the electric charge corresponding to the 
dark current of the photo-diode 32 is stored in the potential well 97, the 
electric charge stored therein is injected into and maintained in the 
charge trapping region in the boundary between the insulating layers 95 
and 96 and the insulating layer 95 itself. The amount of electric charge 
injected into the charge trapping region is in proportion to the number of 
electrons, corresponding to the dark current of the photo-diode 32, stored 
in the potential well 97. 
The height of the potential barrier of the skimming gate in the image 
operation is changed, in the same manner as in the ninth embodiment, in 
accordance with the amount of electrical charge injected into the charge 
trapping region in the boundary between the insulating layers 95 and 96 
and the insulating layer 95 itself. Thus, due to the insulating layers 95 
and 96 in which the electric charge corresponding to the dark current of 
the photo-diode 32 is stored, the signal electric charge to which the 
correction regarding the dark current of the photo-diode 32 is applied can 
be transferred to the transmission portion in the imaging operation in the 
same manner as in the ninth embodiment. 
A description will now be given, with reference to FIGS. 31, 32, 33 and 34, 
of an eleventh embodiment of the present invention. 
Referring to FIG. 33, p-type regions 117 and 118 are formed in an n-type 
substrate 114 so as to be close to the surface of the n-type substrate 
114. The p-type region 115 is connected to the ground line via an 
electrode 115. A gate electrode 120 covered by an insulating film 126 is 
formed between the p-type regions 117 and 118. A floating electrode 121 is 
formed in the insulating film 126 under the gate electrode 120. The gate 
electrode 120 is used to control the bias voltage of a photo-diode 102. 
The floating gate 121 is used to correct the bias voltage in accordance 
with the characteristic of the photo-diode 102. 
An n-type region 106 and an insulating film 104 which are parts of an input 
diode are formed in a p-type substrate 103 so as to be close to the 
surface of the p-type substrate 103. The n-type region 106 is connected to 
the photo-diode 102 corresponding to a pixel via a diode connecting 
electrode 107. The anode of the photo-diode 102 is connected to the p-type 
region 118 via a diode connecting electrode 116. An input gate 108 to 
which an original voltage for the bias voltage of the photo-diode 102 is 
to be supplied, a storage electrode 111, a transfer gate electrode 112 and 
a transmission portion electrode 113 of the vertical CCD 12 are formed on 
a structure including the substrate 103 and an insulating film 105 made of 
SiO.sub.2 so as to be separated from the substrate 103 by the insulating 
film 105. 
In the eleventh embodiment, holes corresponding to the dark current of the 
photo-diode 102 are injected into the floating electrode 121, and the dark 
current of the photo-diode 102 is controlled by the holes injected into 
the floating electrode 121. The details are described below. 
First, under a condition in which no light is incident on the photo-diode 
102, as shown in FIG. 31, a voltage supplied to the input gate 108 is 
controlled so as to correspond to the bias voltage of the photo-diode 102. 
The gate electrode 120 is maintained at a predetermined voltage of about 
-10 volts so that a potential well 131 is formed under the gate electrode 
120. In addition, the storage electrode 111 is controlled so as to be 
maintained at a voltage of about 10 volts so that a potential well 132 is 
formed under the storage electrode 112. The transfer gate electrode 112 is 
maintained at 0 volts so that the transfer gate is shut down. In this 
state, holes corresponding to the dark current of the photo-diode 102 are 
injected into the potential well 131 for a predetermined time. 
After this, as shown in FIG. 32, a high voltage of about -50 volts is 
supplied to the gate electrode 120, so that the holes stored in the 
potential well 131 are injected into the floating electrode 121. 
FIG. 34 shows the potential in a section taken along a line X5-X6 shown in 
FIG. 32. As shown in FIG. 34, the holes stored in the potential well 131 
formed in the substrate 114 tunnel through an insulating portion 123 and 
are injected into the floating electrode 121. The holes are stored in the 
floating electrode 121. The amount of electric charge Q of the holes 
injected into the floating electrode 121 is in proportion to the number of 
holes, corresponding to the dark current of the photo-diode 102, stored in 
the potential well 131. 
The electric charge may be injected into the floating electrode 121 as 
follows. That is, in a state where the electric charge corresponding to 
the dark current is stored in the potential well 131, light having an 
energy exceeding the potential barrier of the insulating portion 123 is 
projected onto the surface of the solid state image sensing device. 
After the electric charge corresponding to the dark current of the 
photo-diode 102 is injected into the floating electrode 121 as described 
above, light is projected onto the photo-diode 102, and the imaging 
operation is carried out. In the imaging operation, as shown in FIG. 33, 
the storage electrode 111 is controlled so as to be maintained at a 
voltage of about 10 volts so that a potential well 133 is formed under the 
storage electrode 111. The signal electric charge is stored in the 
potential well 133. The input gate electrode 108 is maintained at a 
predetermined voltage and the gate electrode 120 is maintained at a 
predetermined voltage of about -1 volt. 
In the imaging operation, a threshold voltage of a virtual transistor 
having a virtual drain and a virtual source which are respectively formed 
of the p-type regions 117 and 118 is shifted in accordance with the amount 
of electric charge injected into the floating electrode 121. The shifting 
of the threshold voltage of the virtual transistor is the same as the 
shifting of the threshold voltage V.sub.th in the first embodiment. 
Due to the shifting of the threshold voltage of the virtual transistor, the 
operating point of the photo-diode 102 is moved in the same manner as that 
of the photo-diode 32 in the first embodiment so that the bias voltage of 
the photo-diode 102 is changed. Thus, the signal electric charge obtained 
based on the correction of the dispersion of the dark currents of the 
photo-diodes in the solid state image sensing device is stored in the 
potential well 133. 
According to the eleventh embodiment, due to the floating electrode into 
which the electric charge corresponding to the dark current of the 
photo-diode 102 is injected, the dispersion of the dark currents of the 
photo-diodes in the solid state image sensing device can be reduced in the 
imaging operation in the same manner as in the first embodiment. 
A description will now be given, with reference to FIG. 35, of a twelfth 
embodiment of the present invention. In FIG. 35, those parts which are the 
same as those shown in FIG. 31 are given the same reference numbers. 
Referring to FIG. 35, a multilayer insulating film having an insulating 
layer 124 made of Si.sub.3 N.sub.4 and an insulating layer 125 made of 
SiO.sub.3 is formed under the gate electrode 120. 
In the twelfth embodiment, after the electric charge corresponding to the 
dark current of the photo-diode 102 is stored in the potential well 131, 
the electric charge is injected into and stored in the charge trapping 
region in the boundary between the insulating layers 124 and 125 and the 
insulating layer 124 itself. The amount of electric charge of the holes 
injected into the charge trapping region is in proportion to the number of 
holes, corresponding to the dark current of the photo-diode 102, stored in 
the potential well 131. 
In the imaging operation, the bias voltage of the photo-diode 102 is 
controlled, in the same manner as the eleventh embodiment, in accordance 
with the amount of electric charge injected into the charge trapping 
region in the boundary between the insulating layers 124 and 125 and the 
insulating layer 124 itself. Thus, in the twelfth embodiment, due to the 
insulating layers 124 and 125 in which the electric charge corresponding 
to the dark current of each photo-diode is stored, the dispersion of the 
dark currents of the photo-diodes in the solid state image sensing device 
can be reduced in the same manner as the eleventh embodiment. 
A description will now be given, with reference to FIG. 36, of a thirteenth 
embodiment of the present invention. In the thirteenth embodiment, the 
input circuit having the function for correcting the dark current of the 
photo-diode as described above is used as an input circuit in the solid 
state image sensing device having a TDI (Time Delay And Integration) 
function. In the solid state image sensing device having the TDI function, 
the signal electric charges obtained from a plurality of photo-diodes for 
one pixel are delayed and added to each other in order to improve the 
signal-to-noise ratio. 
Referring to FIG. 36, four photo-diodes 141.sub.1 -141.sub.4 are provided 
for each pixel. Input circuits 142.sub.1 -142.sub.4 are respectively 
coupled to the photo-diodes 141.sub.1 -141.sub.4. Each of the input 
circuits 142.sub.1 -142.sub.4 has the function of correcting the dark 
current of a corresponding one of the photo-diodes 141.sub.1 -141.sub.4. 
The signal electric charges generated by the photo-diodes 141.sub.1 
-141.sub.4 are controlled by the input circuits 142.sub.1 -142.sub.4 and 
the controlled signal electric charges are delayed and integrated with 
each other by a storage electrode 143. A signal obtained by the 
integrating operation of the storage electrode 143 is supplied to a 
read-out circuit. 
In a general solid state image device having the TDI function, if a 
photo-diode having a large dark current is included in the photo-diodes 
141.sub.1 -141.sub.4, a potential well located under the storage electrode 
143 overflows while the integrating operation is being carried out. On the 
other hand, in the example of the solid state image device shown in FIG. 
36, the signal electric charge output from each of the input circuits 
142.sub.1 -142.sub.4 is controlled in accordance with the dark current of 
a corresponding one of the photo-diodes 141.sub.1 -141.sub.4 so that the 
component corresponding to the dark current is uniform in the signal 
electric charge. Thus, even if a photo-diode having a large dark current 
is included in the photo-diodes 141.sub.1 -141.sub.4, there is no danger 
that the potential well located under the storage electrode 143 will 
overflow. As a result, in the solid state image sensing device having the 
TDI function, the number of photo-diodes for each pixel can be increased. 
The present invention is not limited to the aforementioned embodiments, and 
variations and modifications may be made without departing from the scope 
of the claimed invention.