JP2001057423A - Charge transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To offer a charge transfer device which improves transfer efficiency at the final stage of a charge transfer part without increasing a stray-diffusion capacity of the charged detection part at all, and further which increases the maximum quantity of transferred charge at the final stage. SOLUTION: An output gate electrode 101 of the final stage of a charge transfer part is formed straight regarding a direction of a channel's width 126 and a width 125 of the output gate electrode is made narrower than the width 126 of a transfer channel. The output gate electrode 101 on the transfer channel is surrounded in a U shape with a first final transfer electrode 102 which becomes a charge storage region. The electrode 102 on the transfer channel is further surrounded in a U shape with a second final transfer electrode which becomes a potential barrier region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a charge transfer device, and more particularly, to a charge transfer device for improving transfer efficiency and increasing the amount of transferred charges in the final stage.

[0002]

2. Description of the Related Art A solid-state image pickup device (area sensor, line sensor) widely used in video cameras, digital still cameras, facsimile machines and the like generally includes a photoelectric conversion unit for converting incident light into signal charges, and a photoelectric conversion unit. It comprises a charge transfer section for transferring the converted signal charges to the charge detection section, and a charge detection section for detecting the transferred signal charges as an output signal.

Here, as a charge transfer unit, a two-phase drive CCD (Charge Cou) operated by a two-phase drive pulse is used.
Various driving CCDs are used, such as a three-phase driving CCD that operates with three-phase driving pulses and a four-phase driving CCD that operates with four-phase driving pulses.
In particular, when high-speed driving of megahertz or higher is required, a two-phase driving CCD having a simple driving method is widely used.

Here, a conventional two-phase drive CCD (hereinafter, referred to as a CCD) will be described.
The structure and operation of the CCD will be described. FIG.
FIG. 10 is a cross-sectional view in the transfer direction schematically showing the structure near the final stage of a conventional general CCD, and FIG. 10 is a schematic view of the planar structure near the final stage of a conventional general CCD. 7 and 10, a p-type well 532 is formed on the surface of an n-type substrate 531.
A n-type well 533 is formed.
33 is a channel for transferring charges.

On the n − -type well 533, an output gate electrode 501, a first final transfer electrode 502, a second final transfer electrode 503,
A transfer electrode 504, a second transfer electrode 505, and a reset electrode 506 are formed.

An n-type charge accumulation region 530 is formed under the first final transfer electrode 502 and the first transfer electrode 504 by introducing an n-type impurity such as phosphorus or arsenic, and the remaining region of the transfer channel is formed. It becomes a potential barrier region. Here, the case where the charge accumulation region is formed by introducing an n-type impurity is described. However, a potential barrier region is formed by introducing a p-type impurity such as boron, or the first electrode and the second electrode are formed. In some cases, a method of providing a potential difference between the transfer channels of the two electrodes by giving a voltage difference between the two electrodes may be used.

The first final transfer electrode 502 and the second final transfer electrode 503 and the first transfer electrode 504 and the second transfer electrode 505 are formed as a set, and each set includes a two-phase drive pulse Φ1. , Φ2 are applied alternately. Further, a plurality of sets of the first transfer electrode 504 and the second transfer electrode 505 are formed according to the length of the charge transfer portion, and two-phase drive pulses Φ1 and Φ2 are similarly applied alternately to each set. Is done.

[0008] The signal charges transferred through the charge transfer section by the driving pulses of Φ1 and Φ2 are injected into the floating diffusion layer 510 of the charge detection section via the output gate electrode 501. The injected signal charge is transmitted to the output amplifier 512 as a potential change of the floating diffusion layer 510 according to the amount, and the potential change is amplified by the output amplifier 512 and output as an output signal outside the charge detection unit.

After detecting the charge, a reset pulse ΦR is applied to the reset electrode 506, and the signal charge remaining in the floating diffusion layer 510 is converted into a reset drain 511 (the reset drain 511 is not shown in FIG. From the left edge to the left area). In FIG. 10, 513 denotes a channel edge, 520 denotes a transfer direction, 522 denotes a channel narrowing angle, and 523 denotes a direction along the narrowing.

Next, the operation of the first conventional CCD will be described. FIG. 8 is a timing chart showing the operation of the drive pulse Φ1, Φ2 and the reset pulse ΦR, and FIG. Distribution.

Here, the voltage applied to the output gate electrode 501 is the first final transfer electrode 50 when the drive pulse φ1 is ON.
2 is set to be deeper than the channel potential of the output gate electrode 501 and that the channel potential of the first final transfer electrode 502 is shallower than the channel potential of the output gate electrode 501 when the drive pulse Φ1 is OFF. Have been.

Also, the voltage VR of the reset drain 511
D indicates that when the signal charge is injected into the floating diffusion layer 510, the signal charge does not flow over the output gate electrode 501 and flow back to the first final transfer electrode 502.
It is set to be sufficiently deeper than one channel potential.

Further, a reset pulse ΦR is supplied to the reset electrode 506 so as to be superimposed on the DC voltage. When the reset pulse ΦR is ON, the channel potential of the reset electrode 506 becomes deeper than the reset drain voltage VRD. It is set as follows.

In FIG. 8 and FIG. 9, at time t1, the signal charge Q1 is transferred and accumulated below the first final transfer electrode 502. At the same time, the signal charges in the floating diffusion layer 510 are discharged to the reset drain 511 at the same time when the reset electrode 506 is turned on, and the potential of the floating diffusion layer 510 is set to the reset drain level.

At time t2, the reset electrode 506 is turned off.
The state becomes F, and preparation for injecting signal charges into the floating diffusion layer 510 is performed. When the reset electrode 506 is turned off, a small amount of charge flows back from the channel of the reset electrode 506 to the floating diffusion layer 510, so that the floating diffusion layer 510 is set to a feedthrough level having a slightly lower potential than the reset drain level. .

At time t3, the driving pulse Φ1 is turned off.
The state becomes the F state, and the signal charge Q1 stored in the channel below the first final transfer electrode 502 is injected into the floating diffusion layer 510 via the output gate electrode 501. Here, assuming that the signal charge amount to be injected is Qsig and the total coupling capacitance of the floating diffusion layer 510 is Cfj, the potential change Vsig of the floating diffusion layer 510 is expressed by Vsig = Qsig / Cfj (1) Can be. This potential change Vsig is amplified by the output amplifier 512 and output as an output signal outside the charge detection unit.

At time t1 ', signal charges Q2
Is transferred and accumulated below the first final transfer electrode 502.
At the same time, the signal charge Q1 in the floating diffusion layer 510 is discharged simultaneously with the reset electrode 506 being turned on.
And the potential of the floating diffusion layer 510 is set to the reset drain level again. By repeating the above operation, charge transfer and charge detection of the two-phase driven CCD are realized.

Next, a planar structure near the final stage of the CCD according to the first conventional example will be schematically described with reference to FIG.
From equation (1), in order to increase the potential change Vsig of the floating diffusion layer 510, it is necessary to increase the signal charge amount Qsig and minimize the floating diffusion capacitance Cfj.

Generally, in a two-phase drive CCD, the channel potential difference between the first transfer electrode 504 and the second transfer electrode 505 is C
Since it is limited by the minimum drive voltage of the CD, when increasing the signal charge amount, the channel width of the CCD must be widened.

On the other hand, in order to reduce the floating diffusion capacitance Cfj, it is necessary to form the floating diffusion layer 510 as small as possible. Therefore, the channel width of this portion must be formed as narrow as possible. Therefore, in the final stage of the charge transfer section, the channel width is gradually narrowed from tens of microns to several microns across the floating diffusion layer 510.
Generally, 4 is provided.

However, when such channel narrowing 514 is provided, the following three problems occur. First, as the channel width gradually decreases, a narrow channel effect occurs in the first final transfer electrode 502 and the output gate electrode 501, and the electric field in the transfer direction becomes weaker or the electric field in the transfer reverse direction becomes smaller. Occurs
There arises a problem that transfer efficiency in channel narrowing 514 is degraded.

Second, since the channel area of the first final transfer electrode 502 becomes smaller than the channel area of the first transfer electrode 504, the maximum transfer charge amount of the charge transfer section is limited by the first final transfer electrode 502. A problem arises.

Third, since the transfer distance in the direction 523 along the aperture is much longer than the transfer distance in the transfer direction 520, the electric field in the direction 523 along the aperture becomes weaker, and the first Channel narrowing 51 as well as the problem
4 degrades the transfer efficiency.

In order to solve such a problem, in the technique described in Japanese Patent Application Laid-Open No. 5-63175 (hereinafter referred to as a second conventional example), an output gate electrode and a final transfer electrode are connected to a signal charge. It is convex in the direction opposite to the transfer direction.

Since the operation of the CCD according to the second conventional example is exactly the same as the operation of the CCD according to the first conventional example, the device structure in the vicinity of the last stage of the charge transfer section of the CCD according to the second conventional example is described here. Will be described.

The planar structure near the final stage of the CCD according to the second conventional example has an output gate electrode 60 as shown in FIG.
1. Final transfer electrodes 602, 603, transfer electrodes 604, 6
05 differs from the CCD according to the first conventional example. In FIG. 11, reference numeral 606 denotes a reset electrode;
0 indicates a floating diffusion layer, 611 indicates a reset drain, 612 indicates an output amplifier, 613 indicates a channel edge, 614 indicates a channel narrowing, 620 indicates a transfer direction, 622 indicates a channel narrowing angle, and 623 indicates a direction along the narrowing. .

The most significant features of the CCD according to the second prior art are that the output gate electrode 601, the final transfer electrodes 602, 60
3 is projected in the direction opposite to the transfer direction of the signal charge, and the width of the transfer channel of the output gate electrode 601 and the final transfer electrodes 602 and 603 is effectively enlarged.

By increasing the effective channel width in this manner, a decrease in the channel potential due to the narrow channel effect in channel narrowing 614 is reduced, and the transfer efficiency can be prevented from deteriorating. This has a tentative effect that the channel area of the final transfer electrode 602 is increased and the maximum transfer charge amount of the charge transfer section is increased.

[0029]

In the charge transfer section of the conventional solid-state imaging device described above, in the case of the CCD according to the second conventional example, the output gate electrode and the final transfer electrode are made convex in the direction opposite to the transfer direction. Therefore, the area of the floating diffusion layer increases, and the floating diffusion capacitance Cfj increases.
More specifically, the coupling capacitance between the floating diffusion layer and the P-type well and the coupling capacitance between the floating diffusion layer and the output gate electrode increase.

In a solid-state image pickup device used for a high-definition image input device such as a digital still camera, since the unit pixel size is very small (about 5 μm square), the amount of signal charge obtained per unit pixel is small. . for that reason,
In order to maximize the potential change in the floating diffusion layer, efforts have been made to reduce the floating diffusion capacitance Cfj as much as possible (5 fF or less).

Therefore, in the CCD according to the second conventional example, the floating diffusion capacitance Cfj increases as the area of the floating diffusion layer increases, and as a result, the output signal output from the charge detection unit decreases. Occurs. In order to suppress such an increase in the floating diffusion capacitance Cfj, it is necessary to make the convex shape of the output gate electrode and the final transfer electrode as small as possible.

However, since the improvement of the transfer efficiency and the increase of the transfer charge amount when the channel is narrowed are in a trade-off relationship with the formation of the convex portion of the electrode in this portion, the smaller the convex shape is, the more the above described is. First conventional CCD
The same problems as described above, that is, the problem of deterioration of transfer efficiency due to channel narrowing and the limitation of the maximum transfer charge amount at the first final transfer electrode appear again.

Therefore, an object of the present invention is to solve the above-mentioned problems and to improve the transfer efficiency at the last stage of the charge transfer section without increasing the floating diffusion capacitance of the charge detection section at all. To provide a charge transfer device capable of increasing the maximum transfer charge amount in the above.

[0034]

According to the present invention, there is provided a charge transfer device including a charge transfer unit for transferring a signal charge photoelectrically converted in a solid-state imaging device to a charge detection unit for detecting the signal charge as an output signal. A transfer device, comprising: an output gate electrode disposed at the last stage of the charge transfer unit and including at least one or more electrodes, and having an electrode width on a transfer channel of the output gate electrode being equal to that of the output gate electrode. It is configured to be narrower than the channel width at the position.

That is, in the charge transfer device of the present invention, an output gate electrode composed of at least one or more electrodes is disposed at the last stage of the charge transfer section for transferring signal charges, and the output gate electrode is provided on the transfer channel of the output gate electrode. The electrode width is narrower than the channel width at the position of the output gate electrode.

Further, in the charge transfer device of the present invention, a charge detection unit for detecting a signal charge as an output signal is disposed adjacent to the last stage of the charge transfer unit, and a side of the output gate electrode which is in contact with the charge detection unit is provided. It is characterized by a straight line in a range in contact with the charge detection unit.

Further, in the charge transfer device according to the present invention, a final transfer electrode comprising at least one or more electrodes is further provided at the final stage of the charge transfer unit, and the transfer of the output gate electrode other than the side in contact with the charge detection unit is performed. A final transfer electrode is provided so as to surround the side on the channel, and the signal charge is transferred not only in the channel length direction but also in the channel width direction from the final transfer electrode to the output gate electrode.

Further, in the charge transfer device of the present invention, a charge storage region is provided in the transfer channel below the final transfer electrode so as to surround the output gate electrode, and a potential barrier region is formed so as to surround the charge storage region. It is characterized by being arranged.

The channel width of the charge detecting section may be narrower than the channel width of the charge transferring section, and the transfer channel may be narrowed at a right angle from the charge transferring section to the charge detecting section. Further, the channel width of the charge detection unit is configured to be narrower than the channel width of the charge transfer unit, and the transfer channel may be gradually narrowed from the charge transfer unit to the charge detection unit.

According to the charge transfer device of the present invention, the electrode width of the output gate electrode is configured to be narrower than the transfer channel width at that position, and the charge storage region is provided so as to surround the output gate electrode. Further, by disposing the potential barrier region so as to surround the periphery thereof, even if the transfer channel is narrowed at a sharp angle in the final stage of the charge transfer portion,
Since the narrow channel effect does not occur, it is possible to prevent the transfer efficiency from deteriorating in the final stage.

At the same time, since the channel area of the potential accumulation region below the final transfer electrode is enlarged, it is possible to prevent the maximum transfer charge amount of the charge transfer section from being limited at the last stage. On the other hand, since the area of the floating diffusion layer does not increase, the increase of the floating diffusion capacitance which is a problem in the second conventional example described above does not occur at all.

[0042]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a planar structure near the last stage of a CCD according to a first embodiment of the present invention.
In FIG. 1, the planar structure in the vicinity of the last stage in the CCD of the first embodiment has an output gate electrode 101,
The electrode shapes of the first final transfer electrode 102 and the second final transfer electrode 103 and the narrowing angle 122 of the channel are greatly different from those of the above-described CCDs according to the first conventional example and the second conventional example.

That is, the electrode width 125 of the output gate electrode
Is smaller than the channel width 126 of the transfer channel at the position of the output gate electrode 101, the first final transfer electrode 102 is formed in a U-shape so as to surround the periphery of the output gate electrode 101 on the transfer channel, and the second Last transfer electrode 1
03 is also the first final transfer electrode 102 on the transfer channel.
Is formed in a U-shape so as to surround the periphery of.

The channel narrowing 114 is configured such that the narrowing angle 122 is 90 degrees.
The first transfer electrode 104 and the second transfer electrode 105 are formed in a plurality of stages in accordance with the length of the charge transfer portion, similarly to the CCDs according to the first and second conventional examples described above. 106, the reset drain 111, and the output amplifier 112 are also configured in the same manner as the CCDs according to the first and second conventional examples described above.

Here, the CC according to the first embodiment of the present invention
The principle of operation in D is basically the same as that of the above-described first conventional CCD shown in FIGS. 8 and 9, and a description thereof will be omitted. In FIG. 1, 110 is a floating diffusion layer, 113 is a channel edge, 120 is a transfer direction, 1
21 denotes a channel width direction, 123 denotes a direction along the narrowing, and 130 denotes a charge accumulation region.

Next, the CCD according to the first embodiment of the present invention will be described.
Will be described. According to the first embodiment of the present invention, first, the output gate electrode 101 is connected to the second
In this case, the area of the floating diffusion layer 110 of the charge detection unit does not increase because the charge diffusion layer 110 is formed linearly in the channel width direction 121 without being formed so as to be convex in the direction opposite to the transfer direction as in the conventional example. In addition, an increase in the floating diffusion capacitance Cfj can be suppressed.

Second, by making the electrode width 125 of the output gate electrode smaller than the channel width 126 of the transfer channel, the signal charges in the output gate electrode 101 are not only transmitted in the transfer direction 120 but also in the channel width direction 121. Since it is transferred, the channel narrowing angle 1
22 can be set to 90 degrees, and the influence of the narrow channel effect in channel narrowing 114 can be eliminated. As a result, in the transfer channel below the output gate electrode 101, the electric field in the transfer direction weakens,
Since a problem such as generation of an electric field in the reverse direction of the transfer does not occur, deterioration of the transfer efficiency in this portion can be prevented.

Third, by surrounding the periphery of the output gate electrode 101 on the transfer channel in a U-shape with the first final transfer electrode 102, the signal charge transferred to the channel below the first final transfer electrode 102 becomes Not only the region of the output gate electrode 101 facing the transfer direction 120 but also the channel width direction 12
Since the charge is also accumulated in the region facing 1, the maximum transfer charge amount of the first final transfer electrode 102 can be increased.

Fourth, by surrounding the periphery of the first final transfer electrode 102 on the transfer channel with the second final transfer electrode 103, not only the transfer direction 120 but also the channel width direction 121 with a sufficient transfer electric field. Signal charges can be transferred. In particular, when the electrode length in the channel width direction 121 of the first final transfer electrode 102 is configured to be the same as the electrode length in the transfer direction 120, the transfer electric field in the channel width direction 121 is at the same level as the transfer electric field in the transfer direction 120. To a channel narrowing angle 122 of 9
Even when it is set to 0 degrees, it is possible to improve the transfer efficiency in the channel width direction 121 to about the same as the transfer efficiency in the transfer direction 120.

When the electrode length in the channel width direction 121 of not only the first final transfer electrode 102 but also the second final transfer electrode 103 is made equal to the electrode length in the transfer direction 120, the first final transfer electrode Since the channel area of 102 is equal to the channel area of the first transfer electrode 104,
The maximum transfer charge amount of the charge transfer unit is the first final transfer electrode 102
There is also an effect that the problem of being restricted by the problem does not occur.

Therefore, according to the first embodiment of the present invention, the transfer efficiency at the final stage of the charge transfer section is improved without increasing the floating diffusion capacitance Cfj, and the maximum transfer charge at this final stage is increased. A charge transfer device with an increased amount can be realized.

FIG. 2 shows a CC according to the second embodiment of the present invention.
It is a schematic diagram of a planar structure near the last stage of D. In FIG. 2, the planar structure near the final stage of the CCD according to the second embodiment of the present invention is different from the CCD according to the first embodiment of the present invention in the shape of the channel narrowing 214 at the final stage of the charge transfer section. ing.

That is, in the first embodiment of the present invention, the narrowing angle of the channel is set to 90 degrees, but in the second embodiment of the present invention, the narrowing angle 222 is set to be smaller than 90 degrees. . More specifically, even when the channel is narrowed down, at least a part of the narrowing angle 2 within the range in which at least a part of the side of the output gate electrode 201 facing the channel width direction 221 remains on the transfer channel.
22 is set.

When the aperture angle 222 is reduced in this manner, the transfer electric field in the direction 223 along the aperture becomes the vector sum of the electric field in the transfer direction 220 and the electric field in the channel width direction 221. C according to the embodiment of
The transfer efficiency is further enhanced compared to the CD, and the transfer efficiency at the output stage can be further improved. Note that channel narrowing 214
May be linearly narrowed down from the channel width of the charge transfer section to the channel width of the floating diffusion layer 210 as shown by 214a, or may be narrowed down only below the second final transfer electrode 203 as shown by 214b. Good.

In FIG. 2, 201 is an output gate electrode, 202 is a first final transfer electrode, 203 is a second final transfer electrode, 204 is a first transfer electrode, 205 is a second transfer electrode, 206 is a reset electrode, 210 is a floating diffusion layer, 21
1 is a reset drain, 212 is an output amplifier, 213 is a channel edge, 220 is a transfer direction, and 230 is a charge accumulation region.

In the CCD according to the second embodiment of the present invention,
In addition to the effects obtained by the CCD according to the first embodiment of the present invention, the following effects can be obtained. That is, when the channel is narrowed down as in 214a, the maximum transfer charge amount of the first final transfer electrode 202 is slightly reduced as compared with the CCD according to the first embodiment of the present invention. The transfer electric field in the direction 223 is greatly enhanced, and there is an effect that the transfer efficiency in this portion is greatly improved.

When the channel is narrowed down as in 204b, the maximum transfer charge amount of the first final transfer electrode 202 can be as large as that of the CCD according to the first embodiment of the present invention. , At the same time along direction 2
Since the transfer electric field of 23 can be strengthened as compared with the CCD according to the first embodiment of the present invention, it is possible to simultaneously improve the transfer efficiency in the output stage and increase the maximum transfer charge amount.

The shape of the channel narrowing 214 is as follows.
The output gate electrode 201 is not limited to the above 214a and 214b, and may be freely deformed within a range where at least a part of the side of the output gate electrode 201 facing the channel width direction 221 remains on the transfer channel. .

FIG. 3 shows a third embodiment of the present invention.
FIG. 5 is a cross-sectional view in the transfer direction schematically showing a structure near the last stage of D. In FIG. 3, the CCD according to the third embodiment of the present invention has a configuration in which the final transfer electrode 302 has a one-electrode configuration made of a second-layer polysilicon film, and the final transfer electrode 302 and the second transfer electrode 305. This is different from the CCD according to the first embodiment of the present invention in that an n − -type potential barrier region is formed by ion-implanting a p-type impurity such as boron into the lower n-type transfer channel.

The potential barrier region 33 below the final transfer electrode 302
5 is formed by implanting a p-type impurity into a part of the transfer channel by mask alignment. In such a configuration of the output stage, the transfer channel under the output gate electrode 301 and the charge accumulation region 330 under the final transfer electrode 302 have the same impurity distribution, so that the output gate electrode 301 has a channel potential at the output gate electrode 301. A constant voltage is applied so as to be shallower than the channel potential of the charge storage region 330 under the final transfer electrode 302 at the time of the high level and deeper than the channel potential of the charge storage region 330 under the final transfer electrode 302 at the time of the low level. Is done.

In FIG. 3, reference numeral 304 denotes a first transfer electrode; 306, a reset electrode; 310, a floating diffusion layer;
1 is a reset drain, 312 is an output amplifier, 331 is an n-type substrate, 332 is a p-type well, 333 is an n-type well,
Reference numeral 334 denotes a gate insulating film.

FIG. 4 shows a third embodiment of the present invention.
It is a schematic diagram of a planar structure near the last stage of D. In FIG. 4, the planar structure in the vicinity of the final stage of the CCD according to the third embodiment of the present invention has a U-shaped final transfer electrode 302 so as to surround the periphery of the output gate electrode 301 on the transfer channel.
A potential barrier region 335 is formed in a U-shape by ion-implanting a p-type impurity into the transfer channel below the final transfer electrode 302 at a certain distance from the output gate electrode 301. As a result, a region surrounded by the output gate electrode 301, the potential barrier region 335, and the channel narrowing 314 becomes the charge storage region 330.

As described above, the fact that the charge storage region 330 and the potential barrier region 335 are formed under the final transfer electrode 302 composed of one electrode is the reason for the CCD according to the third embodiment of the present invention. The biggest feature. In FIG. 4, 311 is a reset drain, 313 is a channel edge, 320 is a transfer direction, 321 is a channel width direction, 32
Reference numeral 2 denotes a channel narrowing angle.

Next, a CCD according to a third embodiment of the present invention will be described.
The effect will be described. In the CCD according to the first embodiment of the present invention in which the final transfer electrode is composed of two electrodes, the CCD is disposed between the charge accumulation region and the potential barrier region below the final transfer electrode.
Inevitably, a gap between the electrodes is formed due to the configuration. Such a gap between the transfer electrodes causes a potential dip in a transfer channel below the transfer electrode, and causes a deterioration in transfer efficiency.

In the CCD according to the third embodiment of the present invention,
Since the final transfer electrode 302 is composed of one electrode, no gap between the electrodes is structurally formed between the charge accumulation region and the potential barrier region, and such a potential dent does not occur. Therefore, the CCD according to the third embodiment of the present invention has an effect that the transfer efficiency at the final stage of the charge transfer unit is further improved as compared with the CCD according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a CC according to the fourth embodiment of the present invention.
FIG. 5 is a cross-sectional view in the transfer direction schematically showing a structure near the last stage of D. In FIG. 5, the CCD according to the fourth embodiment of the present invention has two output gate electrodes (401a, 401a).
b) and the second output gate electrode 4
01a, second final transfer electrode 403, second transfer electrode 405
It differs from the CCD according to the first embodiment of the present invention in that a potential barrier region 435 formed by ion-implanting a p-type impurity such as boron into the lower transfer channel is formed.

In the CCD according to the fourth embodiment of the present invention,
Since the transfer channels under the output gate electrodes 401a and 401b and the transfer channels under the final transfer electrodes 402 and 403 have the same impurity distribution, the output gate electrodes 401a and 401b have the same impurity distribution.
In this case, a constant voltage equal to or slightly higher than the high level voltage of the transfer pulse Φ1 supplied to the final transfer electrodes 402 and 403 may be applied.

In FIG. 5, 404 is a first transfer electrode, 406 is a reset electrode, 410 is a floating diffusion layer, 41
Reference numeral 2 denotes an output amplifier, 431 denotes an n-type substrate, 432 denotes a p-type well, 433 denotes an n-type well, and 434 denotes a gate insulating film.

FIG. 6 shows a CC according to the fourth embodiment of the present invention.
It is a schematic diagram of a planar structure near the last stage of D. In FIG. 6, the planar structure near the final stage of the CCD according to the fourth embodiment of the present invention is similar to that of the first output gate electrode 40 on the transfer channel.
A second output gate electrode 401b is formed in a U shape so as to surround the periphery of 1a, and a first final transfer electrode 402 is further formed so as to surround the periphery of the second output gate electrode 401b on the transfer channel. A second final transfer electrode 403 is configured to surround the periphery.

A potential barrier region 43 formed by ion implantation of a p-type impurity is formed in the transfer channel below the second output gate electrode 401b and the second final transfer electrode 403.
5 is formed in the same U-shape as the electrode. FIG.
, 411 denotes a reset drain, 413 denotes a channel edge, 414 denotes a channel narrowing, 420 denotes a transfer direction, 421 denotes a channel width direction, 422 denotes a channel narrowing angle, and 426 denotes a channel width of the transfer channel.

Next, a CCD according to a fourth embodiment of the present invention will be described.
The effect will be described. According to the fourth embodiment of the present invention, since the potential difference is provided between the channel below the first output gate electrode 401a and the channel below the second output gate electrode 401b, the transfer electric field at this portion is reduced by the transfer direction 420 and the transfer direction 420. In both the channel width direction 421, the CCD is strengthened compared to the CCD according to the first embodiment of the present invention.

Therefore, in order to increase the maximum transfer charge amount, the channel width 426 of the transfer channel is set to the value of the first embodiment of the present invention.
Even when the CCD is further expanded than the CCD according to the embodiment, the charge transfer in the channel width direction 421 can be performed with sufficient transfer efficiency. At the same time, the channel area of the first final transfer electrode 402 surrounding the second output gate electrode 401b is increased, so that the maximum transfer charge amount of the first final transfer electrode 402 can be further increased.

In the fourth embodiment of the present invention, the second output gate electrode 401b, the second final transfer electrode 403, and the second transfer electrode 405 are formed of a second-layer polysilicon film. Although the potential barrier region 435 is formed by implanting a p-type impurity, the first output gate electrode 401a, the first final transfer electrode 402, and the first transfer electrode 40 are formed.
The same effect can be obtained even if the charge storage region is formed by injecting an n-type impurity such as phosphorus or arsenic under these electrodes and forming a charge storage region under the second polysilicon film. .

As described above, in the charge transfer device having a structure in which the channel is narrowed from the charge transfer section to the charge detection section, the floating diffusion layer is formed by forming the output gate electrode linearly in the channel width direction. Does not increase, the increase of the floating diffusion capacitance Cfj is suppressed.

Further, the signal width of the output gate electrode is made smaller than the channel width of the transfer channel, and the periphery of the output gate electrode on the transfer channel is surrounded by a final transfer electrode in a U-shape, whereby the signal charge is transferred in the transfer direction. Not only in the channel width direction but also in the channel width direction, so that the channel narrowing angle can be set to 90 degrees or an angle close thereto. As a result, a narrow channel effect in channel narrowing is suppressed, and transfer efficiency in this portion is improved.

At the same time, the signal charges transferred to the charge storage region below the final transfer electrode are stored not only in the region of the output gate electrode facing the transfer direction but also in the region facing the channel width direction. The effect of increasing the maximum transfer charge amount of the electrode is also obtained. It should be noted that the present invention is not limited to the configuration of each of the above embodiments, and it is clear that each embodiment can be appropriately modified within the scope of the technical idea of the present invention.

[0077]

As described above, according to the present invention, in a charge transfer device having a structure in which a channel is narrowed from a charge transfer portion to a charge detection portion, an output gate electrode is linearly arranged in a channel width direction. It is possible to improve the transfer efficiency in the last stage of the charge transfer unit and further increase the maximum transfer charge amount in the last stage without increasing the floating diffusion capacitance of the charge detection unit at all. effective.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a planar structure near a final stage of a CCD according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a planar structure near a final stage of a CCD according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view in a transfer direction schematically showing a structure near a final stage of a CCD according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram of a planar structure near a final stage of a CCD according to a third embodiment of the present invention.

FIG. 5 is a sectional view in the transfer direction schematically showing a structure near the last stage of a CCD according to a fourth embodiment of the present invention.

FIG. 6 is a schematic diagram of a planar structure near a final stage of a CCD according to a fourth embodiment of the present invention.

FIG. 7 is a cross-sectional view in the transfer direction schematically showing a structure near a final stage of a CCD according to a first conventional example.

FIG. 8 is a timing chart of a CCD driving pulse according to the first conventional example.

FIG. 9 is a cross-sectional structure near the last stage of the CCD of the first conventional example 1 and times t1, t2, t3, t in the timing chart.
It is a channel potential distribution in 1 '.

FIG. 10 is a schematic diagram of a planar structure near a final stage of a CCD according to a first conventional example.

FIG. 11 is a schematic diagram of a planar structure near a final stage of a CCD according to a second conventional example.

[Explanation of symbols]

101, 201, 301 Output gate electrode 102, 202, 402 First final transfer electrode 103, 203, 403 Second final transfer electrode 104, 204, 304, 404 First transfer electrode 105, 205, 305, 405 Second transfer electrode 106, 206, 306, 406 Reset electrode 110, 210, 310, 410 Floating diffusion layer 111, 211, 311, 411 Reset drain 112, 212, 312, 412 Output amplifier 113, 213, 313, 413 Channel edge 114, 214, 314,414 Channel narrowing 120,220,320,420 Transfer direction 121,221,321,421 Channel width direction 122,222,322,422 Channel narrowing angle 125 Output gate electrode electrode width 126,426 Transfer channel Channel width 130, 230, 330 Charge storage region 131, 231, 331, 431 N-type substrate 132, 232, 332, 432 P-type well 133, 233, 333, 433 N-type well 134, 234, 334, 434 Gate insulating film 223 Direction along narrowing down 302 Final transfer electrode 335, 435 Potential barrier region 401a First output gate electrode 401b Second output gate electrode

Claims (6)

[Claims] 1. A charge transfer device comprising: a charge transfer unit that transfers a signal charge photoelectrically converted in a solid-state imaging device to a charge detection unit that detects the signal charge as an output signal; It has an output gate electrode which is arranged in a stage and is composed of at least one or more electrodes, and the electrode width of the output gate electrode on the transfer channel is configured to be smaller than the channel width at the position of the output gate electrode. Charge transfer device characterized by the above-mentioned. 2. The charge detection section is disposed adjacent to a final stage of the charge transfer section, and a side of the output gate electrode that contacts the charge detection section is a straight line in a range in contact with the charge detection section. The charge transfer device according to claim 1, wherein: 3. A charge transfer unit, comprising: a final transfer electrode disposed at a final stage of the charge transfer unit and including at least one or more electrodes, and on the transfer channel other than a side of the output gate electrode contacting the charge detection unit. The final transfer electrode is disposed so as to surround a side, and the signal charge extends not only in the channel length direction from the final transfer electrode to the output gate electrode but also in the channel length direction.
3. The charge transfer device according to claim 1, wherein the charge is transferred also in a channel width direction. 4. A charge storage region provided to surround the output gate electrode in the transfer channel below the final transfer electrode, and a potential barrier region provided to surround the charge storage region. The charge transfer device according to claim 3, wherein: 5. The charge detection unit according to claim 1, wherein a channel width of the charge detection unit is smaller than a channel width of the charge transfer unit, and the transfer channel is narrowed at a right angle from the charge transfer unit to the charge detection unit. The charge transfer device according to any one of claims 1 to 4, wherein 6. The charge detection unit according to claim 1, wherein a channel width of the charge detection unit is smaller than a channel width of the charge transfer unit, and the transfer channel is gradually narrowed from the charge transfer unit to the charge detection unit. The charge transfer device according to any one of claims 1 to 4, wherein