JP2004303782A - Charge transfer device and solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excessively suppress the occurrence of undischarged remainders of discharged charges in the charge discharging directions of charge discharging circuits. <P>SOLUTION: A charge transfer device comprises a vertical charge transfer device which has a plurality of steps of charge transfer electrodes and transfers signal charges, a plurality of charge discharging circuits disposed with respect to one step of charge transfer electrodes and selectively discharge the signal charges transferred by means of the vertical charge transfer device in different charge discharging directions, and an output circuit which outputs the signal charges transferred by means of the vertical charge transfer device to the outside. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charge transfer device and a solid-state imaging device using the charge transfer device, and more particularly to a charge discharge structure of the charge transfer device.
[0002]
[Prior art]
Conventionally, in a solid-state imaging device using a charge transfer device, for example, a charge discharge circuit for discharging a signal charge to the outside is provided on a vertical charge transfer device, and a signal charge of an arbitrary horizontal line of a photoelectric conversion element is selected. Thinning out is performed. (For example, refer to Patent Document 1.)
FIG. 3 is a diagram illustrating a charge discharging structure in a charge transfer device of a conventional solid-state imaging device. FIG. 3A is a plan view showing a charge discharging structure in a charge transfer device of a conventional solid-state imaging device.
[0003]
The solid-state imaging device 200 includes a large number of photoelectric conversion elements 81 arranged in a square matrix, a plurality of columns of vertical charge transfer devices (VCCD) 82, a horizontal charge transfer device (HCCD) 83, and an output circuit 84. .
[0004]
The signal charge 87 accumulated in the photoelectric conversion element 81 is vertically transferred from the upper side to the lower side by the adjacent vertical charge transfer device 82. The horizontal charge transfer device 83 receives in parallel the signal charges 87 transferred by the plurality of columns of vertical charge transfer devices 82 and sequentially transfers them to the output circuit 84. The output circuit 84 outputs the signal charge 87 transferred by the horizontal charge transfer device 83 to the outside of the solid-state imaging device 200.
[0005]
A charge discharging circuit 90 is formed in the vicinity of the horizontal charge transfer device 83 at the end of the vertical charge transfer device 82. The charge discharge circuit 90 includes a transfer path 91, a discharge control gate 93, and a discharge drain 95, and can discharge the signal charge 87 transferred by the vertical charge transfer device 82 to the outside of the solid-state imaging device 200.
[0006]
FIG. 3B is a schematic cross-sectional view showing the configuration of the charge discharging circuit 90.
[0007]
The transfer path 91 is formed above the transfer channel 91c with an n-type transfer channel (hereinafter simply referred to as a transfer channel) 91c formed on the surface of the p-well (or p-type substrate) 85 and an insulating film 86 interposed therebetween. The transfer electrode 91e forms one transfer stage of the vertical charge transfer device 82. The transfer voltage supply line 92 supplies the control voltage Φvn to the transfer electrode 91e.
[0008]
The discharge control gate 93 is formed above the discharge channel 93 c, which is a region sandwiched between the transfer channel 91 c of the transfer path 91 and the n-type region formed as the discharge drain 95, and the insulating film 86. And a discharge control gate electrode 93e. The discharge control gate 93 is controlled to be turned on / off by a control voltage Φrc supplied by a discharge control voltage supply line 94. The control voltage Φrc is on when it is in a high level state and off when it is in a low level state.
[0009]
The discharge drain 95 is an n-type region formed on the surface of a p-well (or p-type substrate) 85, and is a drain for discharging the signal charge 87 from the vertical charge transfer device 82 (transfer path 91). It is. The drain voltage supply line 96 supplies the drain voltage Vdr to the drain 95.
[0010]
FIG. 3C is a potential distribution diagram formed in the semiconductor of the charge discharging circuit 90 shown in FIG.
[0011]
The potential 97 is the channel potential of the transfer channel, the potential 98off is the channel potential when the discharge operation of the discharge channel 93c is off (the control voltage Φrc is low level), the potential 98on is the discharge operation of the discharge channel 93c (the control voltage Φrc is high level). ) Channel potential, the potential 99 indicates the drain potential of the charge discharge drain 95.
[0012]
During the normal operation of the solid-state imaging device 200, the charge discharge control electrode 93e maintains an off state (the control voltage Φrc is at a low level), and the signal charge 87 transferred through the vertical charge transfer path 82 is not discharged outside. Then, it is transferred to the horizontal charge transfer device 83. Here, as necessary, when the signal charge 87 is transferred to the transfer channel 91c, the charge discharge control electrode 93e is turned on (the control voltage Φrc is at a high level), and is indicated by a dotted arrow in the figure. As described above, the signal charge 87 can be discharged from the transfer channel 91c to the charge discharge drain 95 via the discharge channel 93c.
[0013]
According to the above-described discharging operation, since a plurality of charge discharging circuits 90 arranged in parallel are performed at a time, the selection of the photoelectric conversion element 81 is performed by switching on / off of the charge discharging control electrode 93e at a specific timing. The signal charges of one horizontal line thus formed can be selectively thinned out.
[0014]
[Patent Document 1] JP-A-6-338524
[Problems to be solved by the invention]
In general, the potential barrier 89 as shown in FIG. 3C may exist in the transfer channel 91c with a certain probability due to, for example, processing variations. If the potential barrier 89 is present, a certain amount or less of charge cannot be discharged to the charge discharge drain 95. In this case, in the above-described charge discharge circuit 90, when the charge discharge control electrode 93e is turned on and the signal charge 87 is discharged to the charge discharge drain 95, the transfer channel 91c having the potential barrier 89 has the potential barrier 89. As a result, the signal charge 87 may be left behind. The signal charge left here is output from the vertical charge transfer path 82 via the horizontal charge transfer device 83 after the discharge operation is completed.
[0016]
For example, when all the signal charges are discharged to the charge discharge drain 95 by the charge discharge circuit 90, the remaining discharge charges are output to the vertical line where the potential barrier 89 exists, and appear as a white line on the reproduction screen. This phenomenon appears as an image in which a white line is superimposed on a signal even in the case of a well-known vertical 1/2 line thinning with a digital still camera or the like, and the image quality is significantly deteriorated.
[0017]
An object of the present invention is to drastically suppress the generation of unremoved charges in the charge discharging direction of the charge discharging circuit.
[0018]
Another object of the present invention is to suppress the occurrence of vertical lines due to residual charge transfer due to potential barriers or potential variations that exist in the transfer channel of the vertical charge transfer device included in the charge discharging circuit. That is.
[0019]
[Means for Solving the Problems]
According to one aspect of the present invention, a charge transfer device includes a plurality of stages of charge transfer electrodes, and a plurality of charge transfer devices are arranged with respect to a vertical charge transfer device that transfers signal charges, and one stage of the charge transfer electrodes, A charge discharging circuit that selectively discharges signal charges transferred by the vertical charge transfer device in different charge discharging directions; and an output circuit that outputs the signal charges transferred by the vertical charge transfer device to the outside.
[0020]
According to another aspect of the present invention, a solid-state imaging device includes a semiconductor substrate, a plurality of photoelectric conversion elements formed on the semiconductor substrate, and a photoelectric conversion element formed above the semiconductor substrate. 3. A vertical charge transfer device for transferring the converted signal charge, and a charge transfer device according to claim 1 or 2 for selectively discharging the signal charge photoelectrically converted at a predetermined position.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a charge discharging structure in the vertical charge transfer device 2 of the solid-state imaging device 101 according to the first embodiment of the present invention.
[0022]
FIG. 1A is a plan view showing a charge discharging structure in the vertical charge transfer device 2 of the solid-state imaging device 101.
[0023]
The solid-state imaging device 101 includes a large number of photoelectric conversion elements 1 arranged in a square matrix, a plurality of vertical charge transfer devices (VCCDs) 2 formed adjacent to each column of the photoelectric conversion elements 1, and a plurality of vertical columns. A horizontal charge transfer device (HCCD) 3 formed at one end of the charge transfer device 2 and an output circuit 4 connected to one end of the horizontal charge transfer device 3 are configured.
[0024]
The signal charge 7 accumulated in the photoelectric conversion element 1 is vertically transferred from the upper side to the lower side by the adjacent vertical charge transfer device 2. The horizontal charge transfer device 3 receives in parallel the signal charges 7 transferred by the plurality of columns of vertical charge transfer devices 2 and sequentially transfers them to the output circuit 4. The output circuit 4 outputs the signal charge 7 transferred by the horizontal charge transfer device 3 to the outside of the solid-state imaging device 101.
[0025]
Near the horizontal charge transfer device 3 at the end of the vertical charge transfer device 2, a first charge discharge circuit 10 and a second charge discharge circuit 20 are formed on the left and right of the same charge transfer stage of the vertical charge transfer device 2. The
[0026]
The first charge discharging circuit 10 includes a transfer path 11, a discharge control gate 13L, and a discharge drain 15L, and selectively converts the signal charge 7 that is photoelectrically converted at a predetermined position and transferred by the vertical charge transfer device 2. It can be discharged outside the solid-state imaging device 101.
[0027]
The second charge discharging circuit 20 includes a transfer path 11 common to the first charge discharging circuit 10, a discharge control gate 13 </ b> R, and a discharge drain 15 </ b> R, and the signal charge discharged by the first charge discharging circuit 10. 7 can be selectively discharged to the outside of the solid-state imaging device 101.
[0028]
FIG. 1B is a schematic cross-sectional view showing the configuration of the first charge discharging circuit 10 and the second charge discharging circuit 20.
[0029]
The transfer path 11 is formed above the transfer channel 11c with an n-type transfer channel (hereinafter simply referred to as a transfer channel) 11c formed on the surface of the p-well (or p-type substrate) 5 and the insulating film 6 interposed therebetween. The transfer electrode 11e forms one charge transfer stage of the vertical charge transfer device 2. The transfer voltage supply line 12 supplies the transfer control voltage Φvn to the transfer electrode 11e. The transfer path 11 forms part of both the charge discharging circuit 10 and the second charge discharging circuit 20.
[0030]
The discharge control gate 13L is formed above the discharge channel 13Lc, which is a region sandwiched between the transfer channel 11c of the transfer path 11 and the n-type region formed as the discharge drain 15L, and the insulating film 6 is interposed therebetween. And a discharge control gate electrode 13Le.
[0031]
The discharge control gate 13R is formed above the discharge channel 13Rc sandwiching the insulating channel 6 and the discharge channel 13Rc sandwiched between the transfer channel 11c of the transfer path 11 and the n-type region formed as the discharge drain 15R. And a discharge control gate electrode 13Re.
[0032]
The discharge control gates 13L and 13R are controlled to be turned on / off by a discharge control voltage Φrc supplied by the discharge control voltage supply line 14. The discharge control voltage Φrc is on when it is in a high level state and off when it is in a low level state.
[0033]
The discharge drains 15L and 15R are formed of an n-type region formed on the surface of the p-well (or p-type substrate) 5, and discharge the signal charge 7 from the vertical charge transfer device 2 (transfer path 11) to the outside. The drain of. The drain voltage supply line 16 supplies the drain voltage Vdr to the discharge drains 15L and 15R.
[0034]
FIG. 1C is a potential distribution diagram formed in the semiconductor of the first charge discharging circuit 10 shown in FIG.
[0035]
The potential 17 is the channel potential of the transfer channel, the potential 18off is the channel potential when the discharge operations of the discharge channels 13Lc and 13Rc are off (the control voltage Φrc is low level), and the potential 18on is the discharge operation of the discharge channels 13Lc and 13Rc (control voltage). The channel potential when Φrc is high), the potential 19, indicates the drain potential of the charge discharge drains 15L and 15R.
[0036]
During the normal operation of the solid-state imaging device 101, the charge discharge control electrodes 13Le and 13Re are kept off (the control voltage Φrc1 is at a low level), and the signal charge 7 transferred through the vertical charge transfer path 2 is discharged to the outside. Without being transferred to the horizontal charge transfer device 3. Here, as necessary, when the signal charge 7 is transferred to the transfer channel 11c, the charge discharge control electrodes 13Le and 13Re are turned on (the control voltage Φrc is at a high level), whereby a dotted arrow in the figure. As shown in FIG. 6, the signal charge 7 can be discharged from the transfer channel 11c to the left and right charge discharge drains 15L and 15R via the discharge channels 13Lc and 13Rc.
[0037]
According to the above-described discharging operation, the signal discharging control electrodes 13Le and 13Re are switched on / off at a specific timing, whereby the signal charges photoelectrically converted by the photoelectric conversion element 1 at a predetermined position can be selectively thinned out. it can.
[0038]
Here, in the common transfer channel 11c, for example, when the potential barrier 9 exists on the first charge discharging circuit side 10 as shown in the figure, a signal charge of a certain amount or less is discharged to the discharge drain 15L. I can't. However, since the potential barrier 9 does not exist in the path to the discharge drain 15R of the second charge discharge circuit 20, a signal charge of a certain amount or less can be discharged through the discharge drain 15R.
[0039]
In addition, for example, even when the potential barrier 9 exists in the approximate center of the common transfer channel 11c, a certain amount or less of the signal charge from the first charge discharging circuit side 10 is discharged through the discharge drain 15L, A certain amount or less of signal charges from the two charge discharge circuit sides 20 are discharged through the discharge drain 15R.
[0040]
As described above, according to the first embodiment of the present invention, the potential barrier 9 does not exist in the path to the drain 15 regardless of the position of the potential barrier 9 in the common transfer channel 11c. A signal charge of a certain amount or less can be discharged through either one of the charge discharging circuit side 10 or the second charge discharging circuit side 20. Therefore, it is possible to eliminate the remaining of signal charges.
[0041]
The configuration shown in FIG. 1A is the same as that of a known square array CCD solid-state imaging device except for the first charge discharging circuit 10 and the second charge discharging circuit 20.
[0042]
FIG. 2 is a diagram showing a charge discharging structure in the vertical charge transfer device 2 of the solid-state imaging device 102 according to the second embodiment of the present invention.
[0043]
FIG. 2 is a diagram showing a charge discharging structure in the vertical charge transfer device 2h of the solid-state imaging device 102 according to the second embodiment of the present invention.
[0044]
The photoelectric conversion elements 1h of the solid-state imaging device 102 are arranged in a matrix with a so-called pixel shift arrangement or a honeycomb arrangement. That is, the pixels in the odd rows and the pixels in the even rows are arranged with a half pitch shift in the horizontal direction, and the pixels in the odd column and the pixels in the even column are arranged with a half pitch shift in the vertical direction.
[0045]
The photoelectric conversion element 1h is basically a rhombus, but has a chamfered shape (strictly, an octagon). By adopting the rhombic pixels in the honeycomb arrangement, the ineffective area can be reduced and the width of the transfer path of the vertical charge transfer device (VCCD) 2h can be formed wide. A plurality of columns of vertical charge transfer devices (VCCDs) 2h arranged along the photoelectric conversion elements 1h in each column are formed by meandering in the vertical direction along the shape of the photoelectric conversion elements 1h.
[0046]
The signal charge 7 accumulated in the photoelectric conversion element 1h is vertically transferred from the upper side to the lower side of the drawing by the adjacent vertical charge transfer device 2h. The horizontal charge transfer device 3 receives in parallel the signal charges 7 transferred by the plurality of columns of vertical charge transfer devices 2 and sequentially transfers them to the output circuit 4. The output circuit 4 outputs the signal charge 7 transferred by the horizontal charge transfer device 3 to the outside of the solid-state imaging device 102.
[0047]
By providing transfer stages 71L and 71R inclined with respect to the vertical as shown in the figure in the vicinity of the horizontal charge transfer device 3 at the end of the vertical charge transfer device 2h, two columns of vertical charge transfer devices 2h adjacent in the horizontal direction are provided. The first charge discharging circuit 30 is formed in the enlarged space. The first charge discharging circuit 30 includes inclined transfer paths 21L and 21R of the left and right vertical charge transfer devices 2h, a discharge control gate 23L, and one discharge drain 25L, and the left and right vertical charge transfers adjacent in the horizontal direction. The signal charge 7 transferred by the device 2h can be discharged outside the solid-state imaging device 102. That is, two adjacent vertical charge transfer devices 2h share one discharge drain 25L.
[0048]
Further, as shown in the figure, the inclined transfer paths 21L and 21R of the first charge discharging circuit 30 are inclined in the opposite direction to the transfer stages 71L and 71R with respect to the vertical, respectively. A second charge discharging circuit 40 having a charge discharging direction different from that of the first charge discharging circuit 30 is formed in the space expanded by 21L and 21R.
[0049]
The second charge discharging circuit 40 includes inclined transfer paths 21L and 21R, a discharge control gate 23R, and one discharge drain 25R of the left and right vertical charge transfer devices 2h, and the left and right vertical charge transfers adjacent in the horizontal direction. The signal charge 7 transferred by the device 2h can be discharged outside the solid-state imaging device 102. That is, two adjacent vertical charge transfer devices 2h share a single discharge drain 25R.
[0050]
Since the discharging principle of the charge discharging circuit is substantially the same as that of the first embodiment, the description thereof is omitted.
[0051]
As described above, in the second embodiment of the present invention, the two vertical charge transfer devices 2h share one discharge drain 25 (25L or 25R), so the number of drains is reduced by half and the horizontal direction The degree of integration can be greatly increased.
[0052]
Further, by providing the second charge discharging circuit 40 having a different charge discharging direction in the same charge transfer stage (transfer channel) 11c as the first charge discharging circuit 30, the charge is charged in the same manner as in the first embodiment. It is possible to eliminate charge remaining due to the charge discharging direction of the discharging circuit.
[0053]
By sharing the drain 25 (25L or 25R), the number of drains is halved compared to the first embodiment described above. Since there are cases where it cannot be shared, the number of drains does not become a full ½ but becomes “about ½”.
[0054]
As described above, according to the embodiment of the present invention, a signal transferred through the vertical charge transfer device is provided by providing a plurality of charge discharge circuits in different charge discharge directions with respect to the charge transfer stage of one vertical charge transfer device. It is possible to drastically reduce the remaining charge discharge, which is a problem when the charge is selectively discharged.
[0055]
For example, if η is the probability that one charge discharging circuit will be left behind, the probability of charge remaining when n charge discharging devices are provided for one vertical charge transfer device is the nth power of η. Decrease. Here, η <1, n ≧ 2 (n is an integer).
[0056]
In each of the first and second embodiments described above, an example in which two charge discharging devices are provided has been described. However, by providing three or more charge discharging devices, there is a charge left behind. Isolation can be reduced.
[0057]
In the first embodiment described above, a square array CCD solid-state imaging device has been described as an example. In the second embodiment, a pixel shift array CCD solid-state imaging device has been described as an example. The second embodiment can also be applied to a square array CCD solid-state image pickup device by applying to a pixel shift array CCD solid-state image pickup device.
[0058]
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0059]
【The invention's effect】
As described above, according to the present invention, it is possible to drastically suppress the generation of undischarged charges in the charge discharging direction of the charge discharging circuit.
[0060]
In addition, according to the present invention, it is possible to suppress the occurrence of vertical lines due to residual charge transfer caused by potential barriers or potential variations that exist in the transfer channel of the vertical charge transfer device included in the charge discharging circuit. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a 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.
FIG. 2 is a diagram showing a charge discharging structure in the vertical charge transfer device 2 of the solid-state imaging device 102 according to the second embodiment of the present invention.
3 is a diagram showing a charge discharging structure in a vertical charge transfer device of a conventional solid-state imaging device 200. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoelectric conversion element, 2 ... Vertical charge transfer apparatus, 3 ... Horizontal charge transfer apparatus, 4 ... Output circuit, 5 ... P well, 6 ... Insulating film, 7 ... Signal charge, 9 ... Potential barrier, 10,30 ... 1st 1 charge discharging circuit, 20, 40 ... second charge discharging device, 11, 21 ... transfer path, 12 ... transfer voltage supply line, 13, 23 ... discharge control gate, 14 ... Ejection control voltage supply line, 15, 25 ... Drain drain, 16 ... Drain voltage supply line, 71 ... Transfer stage, 101,102 ... Solid-state imaging device

Claims (3)

A vertical charge transfer device having a plurality of charge transfer electrodes and transferring signal charges;
A plurality of charge transfer electrodes arranged for one stage of the charge transfer electrode, and selectively discharging signal charges transferred by the vertical charge transfer device in different charge discharge directions;
A charge transfer device comprising: an output circuit for outputting signal charges transferred by the vertical charge transfer device to the outside. The charge discharge circuit has a charge discharge drain shared with other charge discharge circuits having the same corresponding vertical charge transfer device,
2. The charge transfer device according to claim 1, wherein the charge discharge drain is about ½ of the number of columns of the vertical charge transfer device. A semiconductor substrate;
A plurality of photoelectric conversion elements formed on the semiconductor substrate;
A vertical charge transfer device that is formed above the semiconductor substrate and transfers signal charges photoelectrically converted by the photoelectric conversion elements;
A solid-state imaging device having a charge transfer device according to claim 1 or 2, wherein the signal charge photoelectrically converted at a predetermined position is selectively discharged.

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