Charge transfer device and a solid state imaging device using the charge transfer device

An electric charge transfer apparatus comprising a plurality of vertical charge transfer devices for transferring a signal electric charge, a plurality of charge-discharging circuit sets formed next to each of the plurality of vertical charge transfer device, and an output circuit for outputting the signal electric charge transferred by the plurality of charge-discharging circuits to outside of the electric charge transfer apparatus. Each of the plurality of charge-discharging circuit sets includes at least two charge-discharging circuits for discharging the signal electric charge transferred by at least one of adjacent vertical transfer devices consecutively to avoid an electrical barrier caused by left-behind electric charge.

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

A) Field of the Invention

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.

B) Description of the Related Art

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.)

FIGS. 7are drawings showing a charge-discharging structure in the conventional charge transfer device of the solid-state imaging device.FIG. 7Ais a plan view showing a charge-discharging structure in the conventional charge transfer device of the solid-state imaging device.

A solid-state imaging device300is consisted of a multiplicity of photoelectric conversion elements381arranged in a tetragonal matrix, plurality of columns of vertical charge transfer devices (VCCD)382, a horizontal charge transfer device (HCCD)383and an output circuit384.

A signal charge387stored in the photoelectric conversion elements381is vertically transferred from the upper side to the lower side in the drawing by the adjacent vertical charge transfer device382. The horizontal charge transfer device383receives the signal charges387transferred by plurality of columns of the vertical charge transfer devices382in parallel and transfers them to the output circuit384one after another. The output circuit384outputs the signal charges387transferred by the horizontal charge transfer device383to outside of the solid-state imaging device300.

A charge-discharging device390is formed around the horizontal charge transfer device383near the lower end of the vertical charge transfer device382. The charge-discharging device390is consisted of a transfer circuit391, discharging control gate393and a overflow drain395and can discharge the signal charge387transferred by the vertical charge transfer device382to outside of the solid-state imaging device300.

FIG. 7Bis a schematic cross sectional view showing a structure of the charge-discharging device390.

The transfer circuit391is consisted of n-type transfer channel (hereinafter called transfer channel)391cformed on the surface of p-well (or p-type substrate)385, and transfer electrode391eformed above transfer channel391cwith the insulating film386therebetween, and forms one transfer unit of the vertical charge transfer device382. A transfer voltage supplying line392supplies a control voltage φvn to the transfer electrode391e.

The discharging control gate393is consisted of a transfer channel393cwhich is an area between the n-type circuit formed as overflow drain395and the transfer channel391cof the transfer circuit391, and a discharging control gate electrode393eformed above discharging channel393cwith the insulated film386therebetween. Turning on/off of the discharging control gate393is controlled by control voltage φrc supplied by the discharging control voltage supply line394. 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.

The overflow drain395is consisted of an n-type area formed on a surface of the p-well (or p-type substrate)385and is a drain for discharging the signal charge387to the outside. The drain voltage supplying line396supplies a drain voltage Vdr to the drain395.

FIG. 7Cis an electrical potential distribution map formed in a semiconductor of the charge-discharging device390shown inFIG. 7B.

Electrical potential397shows channel electrical potential of the transfer channel, electrical potential398off shows channel electrical potential when the drain operation is turned off (control voltage φrc is in the state of low level), electrical potential398on shows channel electrical potential when the drain operation is turned on (control voltage φrc is in the state of high level), and electrical potential399shows drain electrical potential of the voltage overflow drain395.

During the solid-state imaging elements300is being operated normally, the charge-discharging control electrode393emaintains the state of turned-off (control voltage φrc is being at the low level), and the signal charge387transferred in the vertical charge transfer device382is not discharged to the outside, but is transferred to the horizontal charge transfer device383. Then, depending on necessity, when the signal charge387is transferred to the transfer channel391c, as shown with an dotted arrow in the drawing, by turning on the charge-discharging control electrode393e(making the control voltage φrc at the high level), the signal charge387can be drained from the transfer channel391cto the charge overflow drain395via the discharging channel393c.

According to the above-described operation, since it is operated at once in plurality of the electric charge-discharging device390arranged in parallel, the signal charge of the one horizontal line of the photoelectric conversion element381that was chosen can be alternatively thinned out by changing on-off of electric charge drain control electrode393eat specific timing.

Generally, there may be a potential barrier as shown inFIG. 7Cat a certain probability in the transfer channel391c, for example, by manufacturing unevenness. When there is a potential barrier389, the electric charge below a fixed amount cannot be drained by the charge-discharging device395. In the above-described electric charge-discharging device390, the signal electric charge387may be remained by the electric potential barrier389in the transfer channel391chaving the electric potential barrier389when the signal electric charge387is drained to the charge-discharging device395with the electric charge-discharging control electrode393eturned on. The remained signal electric charge is output from the vertical charge transfer circuit382through the horizontal charge transfer device383after the drain operation finishes.

For example, all the signal electric charges are drained to the charge-discharging device395by the electric charge-discharging device390, the remained electric charge is output from the vertical line having the electric potential barrier389, 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

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.

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.

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.

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.

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.

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.

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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1are diagrams showing an electric charge-discharging structure in a vertical charge transfer device2of a solid-state imaging device101according to a first embodiment of the present invention.

FIG. 1Ais a plan view showing an electric charge flow structure in the vertical charge transfer device2of the solid-state imaging device101.

The solid-state imaging device101is consisted of a multiplicity of photoelectric conversion elements1arranged in a tetragonal matrix, plurality of columns of the vertical charge transfer devices (VCCD)2formed adjacent to each column of the photoelectric conversion elements1, a horizontal charge transfer device (HCCD)3formed at the lower end of the plurality of columns of the vertical charge transfer devices2and an output circuit4connected to the end of horizontal charge transfer device.

A signal electric charge7stored in the photoelectric conversion elements1is transferred from upper side of the drawing to the lower side in vertical by the adjacent vertical charge transfer device2. The horizontal charge transfer device3receives the transferred signal electric charge7in parallel by the plural columns of the vertical charge transfer devices2to transfer to the output circuit4in sequence. The output circuit4outputs the signal electric charge7to the outside of the solid-state imaging device101by the horizontal charge transfer device3.

A first charge-discharging device10and a second charge-discharging device20are formed serially on the same side at the end of the vertical charge transfer device2near the horizontal charge transfer device3. The first charge-discharging device10is consisted of a transfer circuit11, a discharging control gate13and an overflow drain15and can selectively discharge the signal electric charge7photo-electric converted at a predetermined position and transferred in the vertical charge transfer device2to the outside of the solid-state imaging device101. The second charge-discharging device20is consisted of a transfer circuit21, a discharging control gate23and an overflow drain25and can discharge the signal electric charge8left by the charge-discharging device10to the outside the solid-state imaging device101.

FIG. 1Bis a schematic cross sectional view showing a structure of the first charge-discharging device10.

The transfer circuit11is consisted of an n-type transfer channel (hereinafter called just the transfer channel)11cformed on a surface of a p-well (or a p-type substrate)5and a transfer electrode11eformed upper side of the transfer channel11cwith an insulating film6formed therebetween, and forms one transfer unit of the vertical charge transfer device2. A transfer voltage supplying line12supplies a first transfer control voltage φvn1to the transfer electrode11e.

The discharging control gate13is consisted of a discharging channel13cwhich is an area between the n-type area formed as a discharging circuit15and a transfer channel11cof the transfer circuit11, and a discharging control gate electrode13eformed above discharging channel13cwith the insulated film6therebetween. Turning on/off of the discharging control gate13is controlled by first discharging control voltage φrc1supplied by the discharging control voltage supplying line14. Moreover, when the first discharging control voltage φrc1is in a state of high level, it is turned on, and when the discharging control voltage φrc1is in a state of low level, it is turned off.

The overflow drain15is 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 charge7to the outside. The drain voltage supplying line16supplies the first drain voltage Vdr1to the overflow drain15.

FIG. 1Cis an electric potential distribution map formed in a semiconductor of the first charge-discharging device10shown inFIG. 1B.

Each of electric potential17, electric potential18off, electric potential18on and electric potential19indicates channel electric potential of the transfer channel, channel electric potential at a time of drain operation off (when the control voltage13cis at the low level) of the discharging channel13c, channel electric potential at a time of drain operation on (when control voltage φrc1is at the high level) of the discharging channel13cand drain electric potential of the charge-discharging device15.

During a normal operation of the solid-state imaging elements101, the charge-discharging control electrode13emaintains the state of turned-off (control voltage φrc1is at the low level), and the signal charge7transferred at the vertical charge transfer device2is not discharged to the outside, but is transferred to the horizontal charge transfer device3. Then, depending on necessity, when the signal charge7is transferred to the transfer channel11c, as shown with a dotted arrow in the drawing, by turning on the charge-discharging control electrode13e(making the control voltage φrc1at the high level), the signal charge7can be drained from the transfer channel11cto the charge overflow drain15via the discharging channel13c.

According to the above-described operation, the signal charge photoelectric converted by the photoelectric conversion element1at a specific timing can be alternatively thinned out by changing on-off of electric charge drain control electrode13eat the specific timing.

Moreover, for example, when an electric potential barrier9exists in the transfer channel11cof the first charge-discharging device10, all of the signal electric charge7cannot be drained, and left-behind electric charge8(FIG. 1E) may be left in the transfer channel11c.

FIG. 1Dis a schematic cross sectional view showing structure of the second charge-discharging device20.

The transfer circuit21is consisted of a n-type transfer channel (hereinafter called just the transfer channel)21cformed on the surface of the p-well (or the p-type substrate)5and a transfer electrode21eformed upper side of the transfer channel21cwith the insulating film6therebetween, and forms one transfer unit of the vertical charge transfer device2. A transfer voltage supplying line22supplies a second transfer control voltage φvn2to the transfer electrode21e.

The discharging control gate23is consisted of a discharging channel23cwhich is an area between the n-type area formed as discharging circuit25and the transfer channel21cof the transfer circuit21, and a discharging control gate electrode23eformed above the discharging channel23cwith the insulated film6therebetween. Turning on/off of the discharging control gate23is controlled by second discharging control voltage φrc2supplied by the discharging control voltage supplying line24. Moreover, when the second discharging control voltage φrc2is in a state of the high level, the discharging control gate23is turned on, and when the discharging control voltage φrc2is in a state of the low level, it is turned off.

The overflow drain25is 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 charge8to the outside. The drain voltage supplying line26supplies the second drain voltage Vdr2to the overflow drain15.

FIG. 1Eis an electric potential distribution map formed in the semiconductor of the second charge-discharging device20shown inFIG. 1D.

Each of electric potential27, electric potential28off, electric potential28on and electric potential29indicates channel electric potential of the transfer channel, channel electric potential at a time of drain operation off (when the control voltage φrc2is at the low level) of the discharging channel23c, channel electric potential at a time of drain operation on (when control voltage φrc2is at the high level) of the discharging channel23cand drain electric potential of the charge-discharging device25.

During a normal operation of the solid-state imaging elements101, the charge-discharging control electrode23emaintains the state of being turned-off (control voltage φrc2is at the low level), and the signal charge7that is transferred in the vertical charge transfer device2is not discharged to the outside, but is transferred to the horizontal charge transfer device3. Then, after the electric charge-discharging operation (after transferring the left-behind electric charge8to the transfer channel21c) by the first charge-discharging device10, as shown with an dotted arrow in the drawing, by turning on the charge-discharging control electrode23e(making the control voltage φrc2being high level), the signal charge8can be drained from the transfer channel21cto the charge overflow drain25via the discharging channel13c.

As described in the above, in the first embodiment of the present invention, by providing the second charge-discharging device20under the first charge-discharging device10, the left-behind electric charge8left by the first charge-discharging device10can be drained by the second charge-discharging device20. Therefore, the left-behind electric charge8can be cleared almost completely.

Since it is considered that the probability that the electric potential barrier9exists in the first charge-discharging device10, and the probability that the electric potential barrier9exists in the second charge-discharging device20are 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 devices10and20is “ 1/100”, the probability that an electric charge will be left in both the first charge-discharging device10and the second charge-discharging device20becomes “ 1/10,000”, and can obtain the large improvement effect.

Moreover, although in the embodiment of the present invention, only the first charge-discharging device10and the second charge-discharging device20are 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 “ 1/100”, the probability that an electric charge will be left in all the charge-discharging devices becomes “ 1/1,000,000”, and charge-discharging device probability of electric charge-discharging will be near “0” substantially.

Moreover, the structure shown inFIG. 1Ais the same as well-known square lattice arranged CCD solid-state imaging device except the first charge-discharging device10and the second charge-discharging device20.

FIGS. 2are diagrams showing an electric charge-discharging structure in the vertical charge transfer device2of a solid-state imaging device102according to a second embodiment of the present invention.

FIG. 2Ais a plan view showing structure of charge-discharging device in the vertical charge transfer device2of a solid-state imaging device102. The solid-state imaging device102is different from the above-described first embodiment in a point that the electric charge-discharging directions of the first charge-discharging device10and the charge-discharging device30. Since other structure and operation is the same as the first embodiment, the explanations of them will be omitted.

FIG. 2Bis a schematic cross sectional view showing structure of the first charge-discharging device10, andFIG. 2Dis a schematic cross sectional view showing structure of a second charge-discharging device30. Since structure of the first charge-discharging device10is the same as the structure of the charge-discharging device10shown inFIG. 1B, the explanation for it is omitted. Also, the detailed explanation of the second charge-discharging device30will be omitted because only difference between the second charge-discharging device20shown inFIG. 1Dand the second charging discharging device30is that local relationship among each parts are mirror symmetries.

As shown inFIG. 2BandFIG. 2D, the first charge-discharging device10has the discharging control gate13positioned on the left side of the transfer device11, and the signal electric charge7is discharged to the left-side drain15. On the other hand, the second charge-discharging device30has the discharging control gate33positioned on the right side of the transfer device31, and left-behind electric charge8is discharged to the right-side drain35.

As described in the above, an advantage of making discharging directions of the first charge-discharging device10and the second charge-discharging device30symmetry is explained by referring electric potential distribution maps shown inFIG. 2CandFIG. 2E.

When the electric potential barrier9is extended to a vertical direction in vertical charge transfer device2(transfer channels11cand31c), as shown in the drawing, it exists discharging channel13cside in the transfer channel11c, and it exists opposite side of the discharging channel33cin the transfer channel31c. In this case, when charge-discharging direction of the first charge-discharging device10and the second charge-discharging device20is same, the left-behind electric charge cannot be avoided. However, as in this second embodiment, the left-behind electric charge8can be discharged to the overflow drain35where is the opposite side of the first charge-discharging device10by making the charge-discharging directions of the first charge-discharging device10and the second charge-discharging device30reversed.

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.

FIGS. 3are diagrams showing an electric charge-discharging structure in a vertical charge transfer device2hof a solid-state imaging device103according to a third embodiment of the present invention.

FIG. 3Ais a plan view showing a charge-discharging structure in the vertical charge transfer device2of a solid-state imaging device3.

Photoelectric conversion elements1hof the solid-state imaging device103are disposed in a matrix with a so-called pixel interleaved arrangement (PIA) or the honeycomb arrangement. That is, the photoelectric conversion elements1hin 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 elements1h, and the photoelectric conversion elements1hin the even number columns and in the odd number columns are shifted in the vertical direction by about a half pitch of photoelectric conversion elements1h. 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.

The photoelectric conversion elements1hare 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)2hcan be formed. Plural columns of the vertical charge transfer devices (VCCD)2harranged along the photoelectric conversion elements1hof each column are formed by slaloming along the shape of photoelectric conversion elements1h.

The signal electric charges7stored in the photoelectric conversion elements1hare transferred from upper side to downward vertically by the adjacent vertical charge transfer device2h. The horizontal charge transfer device3receives the signal electric charges7transferred by the plural columns of the vertical charge transfer devices2in parallel and transfers to output circuit4in sequence. The output circuit4outputs the signal electric charges7transferred by the horizontal charge transfer device3to the outside of the solid-state imaging device103.

By providing a transfer line71that is inclined to the verticality, as shown in the drawing, near the end of the vertical charge transfer device2hclose to the horizontal charge transfer device3, two columns of the adjacent vertical charge transfer devices2hare made to be closer and the first charge-discharging device40is formed in an enlarged space. The first charge-discharging device40is consisted of the transfer circuits41L and41R of the vertical charge transfer device2hon either side, discharging controlling gates43L and43R on either side and one overflow drain45, and can discharge the signal electric discharge7transferred at the vertical charge transfer devices2hon either side that is adjacent horizontally to the outside the solid-state imaging device103. That is, adjacent two columns of the vertical charge transfer devices2hshare one overflow drain45.

Moreover, as shown in the drawing, a transfer line72that is inclined to the opposite direction of the transfer line71vertically is provided in the latter line of the first charge-discharging device40, and a second charge-discharging device50with different electric discharging direction from the first charge-discharging device40in a space that is enlarged by the inclined transfer line72.

FIG. 3Bis a schematic cross sectional view showing structure of the first charge-discharging device40. Moreover, the explanation for the second charge-discharging device50will be omitted because the only difference between the second charge-discharging device50and the first charge-discharging device40is that the second charge-discharging device50corresponds to the vertical charge transfer device2hshifted one column to a horizontal direction and other structure and operation are almost the same.

Discharging control gate43L and43R, each of which is consisted of discharging control electrode43eand discharging channel43care formed on both sides of the overflow drain. Moreover, transfer circuits41L and41R each of which is consisted of transfer electrode41eand transfer channel41care formed to the outside of the discharging control gate43L and43R. The signal electric charges7of the transfer circuit41L and41R are discharged by the discharging control gates43L and43R which are turned on at the same time from the same overflow drain45.

FIG. 3Cis an electric potential distribution map formed in the semiconductor of the first charge-discharging device40shown inFIG. 3B.

Electrical potential47indicates channel electrical potential of the transfer channel41c. Electrical potential48off indicates channel electrical potential at a time of discharging operation is turned off (when control voltage φrc3is at the low level) of the discharging channel43c. Electrical potential48on indicates channel electrical potential at a time of discharging operation (when the control voltage φrc3is at the high level) of the discharging channel43c. Electrical potential49indicates drain electrical potential of the charge-discharging device45.

When the signal electric charges are transferred to the transfer channels on right and left sides, the signal electric charges7can be discharged from the transfer channels on both sides to the charge-discharging device45via the discharging channels43con right and left sides as shown with dotted arrows in the drawing by making right and left side of the electric charge control electrodes43eturned on (making the control voltage φrc3at the high level).

In the second electrical charge-discharging device50, 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 device40.

As described in the above, in the third embodiment of the present invention, since two columns of the vertical charge transfer devices2hshare one overflow drain45, 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 device50that discharges to the different direction at lower line of the first charge-discharging device40.

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.

FIG. 4is a diagram showing an electric charge discharging structure in the vertical charge transfer device2hof a solid-state imaging device104according 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.

The difference from the before-described third embodiment is that the first charge-discharging device60and the second charge-discharging device70are formed in a same space. In this case, as shown in the drawing, the overflow drains of the first charge-discharging device60and the second charge-discharging device70is combined together, and it can be one overflow drain65. 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.

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.

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<1 and n≧2 (n indicates an integer).

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.

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.

FIGS. 5are diagrams showing an electric charge discharging structure in the vertical charge transfer device82of the solid-state imaging device201according to a first embodiment of the present invention.

FIG. 5Ais a plan view showing the electric charge-discharging structure in a vertical charge transfer device82of a solid-state imaging device201.

The solid-state imaging device201is consisted of a multiplicity of photoelectric conversion elements81arranged in a tetragonal matrix, plurality of columns of vertical charge transfer devices (VCCD)82formed adjacent to each column of the photoelectric conversion elements81, a horizontal charge transfer device (HCCD)83formed at the end of the plurality of columns of vertical charge transfer devices82and an output circuit84connected to the end of the horizontal charge transfer device.

Signal electric charges87stored in the photoelectric conversion elements81are transferred from upper side of the diagram to the lower side in vertical by the adjacent vertical charge transfer device83. The horizontal charge transfer device83receives the transferred signal electric charges87in parallel by the plural columns of the vertical charge transfer devices82to transfer to an output circuit84in sequence. The output circuit84outputs the signal electric charges87to the outside of the solid-state imaging device201by the horizontal charge transfer device83.

A first electric charge-discharging device210and a second electric charge-discharging device220are formed serially at the end of the vertical charge transfer device82near the horizontal charge transfer device83.

The first electric charge-discharging device210is consisted of a transfer circuit211, an discharging control gate213and an overflow drain215and can selectively discharge the signal electric charge87photo-electric converted at a predetermined position and transferred in the vertical charge transfer device82to the outside the solid-state imaging device201.

The second charge-discharging device220is consisted of a transfer circuit211, a discharging control gate213R and an overflow drain215R and can discharge the signal electric charge87photo-electric converted at the same position of the signal electric charge87discharged at the charge-discharging device210to the outside the solid-state imaging device201.

FIG. 5Bis a schematic cross sectional view showing a structure of the first charge-discharging device210and the second charge-discharging device220.

The transfer circuit211is consisted of an n-type transfer channel (hereinafter called just the transfer channel)211cformed on a surface of a p-well (or a p-type substrate)85and a transfer electrode211eformed upper side of the transfer channel211cwith an insulating film86therebetween, and forms one electric charge transfer unit of the vertical charge transfer device82. A transfer voltage supplying line212supplies a first transfer control voltage φvn1to the transfer electrode211e. Moreover, the transfer circuit211is a part of the electric charge-discharging device210and the second charge-discharging device220.

The discharging control gate213L is consisted of a discharging channel213Lc which is an area between the n-type area formed as overflow drain215L and a transfer channel211cof the transfer circuit211, and a discharging control gate electrode213Le formed above the discharging channel213Lc with the insulated film86therebetween.

A discharging control gate213R is consisted of a discharge channel213Rc which is an area between the n-type region formed as the overflow drain215R and the transfer channel211cof the transfer circuit211, and a discharging control gate electrode213Re formed above discharging channel213Rc with the insulated film86therebetween.

Turning on/off of the discharging control gates213L and213R are controlled by discharging control voltage φrc supplied by the discharging control voltage supplying line214. Moreover, when the first discharging control voltage φrc1is at the high level, the discharging control gates213L and213R are turned on, and when the discharging control voltage φrc1is at the low level, the discharging control gates213L and213R are turned off.

The overflow drains215L and215R, 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 charges87to the outside. The drain voltage supplying line216supplies the drain voltage Vdr to the overflow drains215L and215R.

FIG. 5Cis an electric potential distribution map formed in a semiconductor of the first charge-discharging device210shown inFIG. 5B.

Each of electric potential217, electric potential218off, electric potential218on and electric potential219indicates 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 channels213Lc and213Rc, channel electric potential at a time of drain operation on (when control voltage φrc is high level) of the discharging channels213Lc and213Rc and drain electric potential of the charge-discharging device215L and215R.

During a normal operation of the solid-state imaging elements201, the charge-discharging control electrodes213Le and213Re maintain the state of turned-off (control voltage φrc is at the low level), and the signal charges87transferred at the vertical charge transfer device82are not discharged to the outside, but are transferred to the horizontal charge transfer device83. Then, depending on necessity, when the signal charges87are transferred to the transfer channel211c, as shown with dotted arrows in the drawing, by turning on the charge-discharging control electrodes213Le and213Re (making the control voltage φrc at the high level), the signal charges87can be discharged from the transfer channel211cto the charge overflow drains215L and215R on right and left sides via the discharging channels213Lc and213Rc.

According to the above-described operation, the signal charges photoelectric converted at the photoelectric conversion element81at a specific timing can be alternatively thinned out by changing on-off of electric charge drain control electrodes213Le and213Re at the specific timing.

For example, as shown in the drawing, an electrical potential barrier89exists in the first charge-discharging device side210in a common transfer channels, the signal electric charge below fixed quantity cannot be discharged to the overflow drain215L. However, in the process which results in the overflow drain215R of the second electric charge-discharging circuit220, the electrical potential barrier89does not exist, and the signal electric charge below fixed quantity can be discharged through overflow drain215R.

Moreover, for example, even when the potential barrier9exists in the center mostly in the common transfer channels211c, the signal electric charge below the fixed quantity from the first electric charge-discharging device210side is discharged through overflow drain215L, and the signal electric charge below the fixed quantity from the second electric charge-discharging circuit220side is discharged through overflow drain215R.

As described in the above, according to the fifth embodiment of the present invention, even if the electrical potential barrier89exists in the common transfer channel211c, the signal electric charge below the fixed quantity can be discharged through either one of the first charge-discharging device210side and the second charge-discharging device220side on which the electrical potential barrier89does not exist. Therefore, left-behind electric charge can be removed.

Moreover, the structure shown inFIG. 5Ais similar to the well-known CCD solid-state imaging device in a tetragonal matrix except the first charge-discharging device210and the second charge-discharging device220.

FIG. 6is a diagram showing an electric charge-discharging structure in the vertical charge transfer device82hof the solid-state imaging device202according to a sixth embodiment of the present invention.

Photoelectric conversion elements81hof the solid-state imaging device202are disposed in a matrix with a so-called pixel interleaved arrangement or the honeycomb arrangement. That is, the photoelectric conversion elements81hin 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 elements81h, and the photoelectric conversion elements81hin the even number columns and in the odd number columns are shifted in the vertical direction by about a half pitch of photoelectric conversion elements81h.

The photoelectric conversion elements81hare 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)82hcan be formed. Plural columns of the vertical charge transfer devices (VCCD)82harranged along the photoelectric conversion elements1hof each column are formed by slaloming along the shape of photoelectric conversion elements81h.

The signal electric charges87stored in the photoelectric conversion elements81hare transferred from upper side to downward vertically by the adjacent vertical charge transfer device82h. The horizontal charge transfer device83receives the signal electric charges87transferred by the plural columns of the vertical charge transfer device82in parallel and transfers to output circuit84in sequence. The output circuit84outputs the signal electric charges87transferred by the horizontal charge transfer device83to the outside the solid-state imaging device202.

By providing a transfer lines271L and271R that is inclined to the verticality as shown in the diagram around the horizontal charge transfer device83at the end of the vertical charge transfer device82h, the vertical charge transfer devices82hhorizontally adjoining each other are made closer, and the first charge-discharging device230is formed in an enlarged space. The first charge-discharging device230is consisted of the inclined transfer circuits221L and221R of the vertical charge transfer device82hon either side, discharging controlling gate223L and one overflow drain225L, and can discharge the signal electric discharge87transferred at the vertical charge transfer devices82hon either side that is adjacent horizontally to the outside the solid-state imaging device202. That is, adjacent two columns of the vertical charge transfer devices82hshare one overflow drain225.

Moreover, as shown in the drawing, a inclined transfer circuit221L and221R of the first charge-discharging device is inclined to the opposite direction of the transfer lines271L and271R vertically, and a second charge-discharging device240with different electric discharging direction from the first charge-discharging device230in a space that is enlarged by the inclined transfer lines221L and221R.

The second charge-discharging device240is consisted of the inclined transfer circuits221L and221R of the vertical charge transfer device82hon both sides, discharging control gate223R and one overflow drain225R, and can discharge the signal electric charge87transferred at the vertical charge transfer devices on both sides which are adjacent horizontally to the outside the solid-state imaging device202. That is, it has structure that adjacent two columns of vertical charge transfer devices82hshare one overflow drain.

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.

As described in the above, according to the sixth embodiment of the present invention, since two columns of the vertical charge transfer devices82hshare one overflow drain225(225L or225R), the number of the drains decreases half, and intensity of the horizontal direction will be increased.

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 device240that has different charge-discharging direction on the charge transfer line (transfer channel)211that is same as the first charge-discharging device230.

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.

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.

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<1 and n≧2 (n indicates an integer).

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.

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.

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.