JPH04364738A - Charge transfer device - Google Patents

Abstract

PURPOSE:To provide a charge transfer device excellent in charge transfer speed and efficiency by employing a constitution which positively utilizes a variation in potential to have potential gradient in a transfer direction. CONSTITUTION:A feature is to have an isolating means 5 which is arranged between a plurality of charge transfer elements 27 28 to bring only a part of the elements 27 28 in continuity and to make one electrode 3 of a plurality of electrodes 1, 2, 3 constituting those charge transfer elements 27, 28 overlap another adjacent electrode 4 at a predetermined position with an overlap shape enlarged in a charge transfer direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge transfer device that transfers charges using a charge coupled device or a charge transfer device (hereinafter abbreviated as CCD).

0002

2. Description of the Related Art CCDs are being actively developed as imaging devices because they have many advantages such as a simple structure. In addition, recently there has been a particular demand for high image quality, and CCD
There has also been an increasing demand for higher resolution and faster transfer frequencies. In order to meet these demands, conventional CCDs have adopted a method of using a plurality of horizontal CCDs (hereinafter abbreviated as HCCD) and halving the transfer frequency. This not only halved the transfer frequency, but also had the advantage of halving the HCCD density and lowering power consumption. As a typical example, the one described in Japanese Patent Application Laid-open No. 189966/1983 is known.

FIG. 5 is a partially enlarged view of conventional HCCDs 27 and 28. In FIG. 5, two HCCDs 27 and 28 are provided, and a transfer electrode 29 is provided between them. H
CCDs 27 and 28 are connected to the same F through composite electrodes 25 and 26.
It is connected to D (floating diffusion layer) 30. Transfer electrode 21
, 22, 23, and 24 are two-phase drive CCDs;
4. Store and transfer charge below. Also, synthetic electrodes 25, 26
The relationship between the transfer electrodes 21, 22, 23, and 24 is similar to that of a two-phase drive CCD. Further, it is assumed that the transfer electrode 29 is formed of a first layer of polysilicon, the transfer electrodes 22 and 24 are formed of a second layer of polysilicon, and the transfer electrodes 21 and 23 are formed of a third layer of polysilicon.

First, in the direction of arrow 31, the signal charge is HCC
The light is transferred to the transfer electrodes 22 and 24 of D27. It is transferred to below the transfer electrode 22 of the HCCD 28 as shown by the arrow 36 using the transfer electrode 29 . In the figure, reference numerals 38 and 40 are separating parts, which are composed of channel stoppers. After that, H.C.
Driving pulses φH11 and φH12 are applied to the transfer electrodes of CDs 27 and 28, respectively. After that, the charge is two H
The signals are transferred to the CCDs 27 and 28, and then transferred to the FD 30 via the composite electrodes 25 and 26 and the output electrode 34.

FIG. 6 is an explanatory diagram of driving pulses, and the operation will be explained in more detail using this diagram. φT to transfer electrode 29
G is connected to the composite electrodes 25 and 26 through the terminal 39 through φAG
However, φR is applied to the reset electrode 35. T=t0
Here, the transfer from the VCCD (not shown, but above the arrow 31) to the HCCD 27 has been completed. T
Since φTG is in the ON state at =t1, the charge in the A region of the HCCD 27 in FIG. 5 passes through the transfer electrode 29 and is transferred to the HCCD 28. Furthermore, the charge in the B region is blocked by the separation section 40 and therefore remains in the HCCD 27 . T=t
2, φH12=OFF, so A of HCCD27
All charges in the area are transferred under the transfer electrode 29 and HCCD 2.
Transferred to 8. Also, since φH11 is in the ON state,
The charges in region B still remain on the transfer electrode 22 of the HCCD 27. At T=t3, φTG=OFF, so all the charges existing under the transfer electrode 29 are transferred to HCCD2.
It is transferred to the transfer electrode 22 of No. 8.

In this way, charge is transferred between the HCCDs 27 and 28, the charges are separated into the two HCCDs 27 and 28, and then the charges are transferred to the FD3 using φH12 and φH11.
Transfer in direction 0. As a result, φH11 and φH12 are 2
The frequency is half of that required when using HCCDs 27 and 28 that are not separated into two.

[0007]

[Problems to be Solved by the Invention] However, there are various problems with such a configuration. FIG. 7 is a potential explanatory diagram of a conventional example. As density increases, the pitch in the X direction in FIG. 5 becomes shorter. Generally, when the distance between the electrodes becomes short, a narrow channel effect appears in which the potential becomes shallower. Therefore, a case where a narrow channel effect occurs in the conventional example will be explained.

[0008] Since the electrodes are somewhat uneven in minute areas due to the influence of manufacturing processes, etc., the distance between the electrodes also varies slightly. If we pay attention to the potential distribution in the Y direction, it will become deeper when the distance between the electrodes is wide because it is affected by the narrow channel effect, and conversely, it will be shallower if the distance between the electrodes is narrower. As a result, unevenness of potential occurs in the Y direction according to the distance between the electrodes, and HCCD2
When data is transferred from 7 to HCCD 28, there is a remaining transfer (hatched portion in FIG. 7(a)). The remainder of this transfer is α
If so, the charge at the next stage of the HCCD 27 is increased by +α to the actual charge amount, and the charge amount transferred to the HCCD 28 is decreased by α. These become FPN (fixed pattern noise) and cause a significant deterioration of image quality.

[0009] The occurrence of these potential irregularities is due to the HCCD27
not only. The separation region distance γ under the transfer electrode 29 is
It may become narrower than the width β (in the X direction) of the transfer electrode 24 of the HCCD 27 (see (b) in the figure), or a recess may be formed in the transfer direction. At these times, a convex portion of potential is generated at the location of the transfer electrode 29 (FIG. 2(c)), and the transfer from the HCCD 27 to the bottom of the transfer electrode 29 cannot be performed sufficiently. As a result, FPN has occurred.

[0010] Furthermore, even if the opposing sides between the separation parts 40 can be constructed in parallel, the potential flat part (parallel part) is long, so that in the latter half of the charge transfer, the charge reverses and transfer remains. There is.

The same thing can be done from below the transfer electrode 29 to the HCCD.
This also applies to transfers to 28.

As described above, due to the narrow channel effect that appears with the increase in density, residual charge transfer occurs in various parts, resulting in a problem of significant image quality deterioration due to FPN and the like. This problem was inevitable because the narrow channel effect was unavoidable if higher density was required.

The present invention has been made in view of the problems of the conventional charge transfer device, and it is possible to transfer charges by actively utilizing changes in potential and by adopting a configuration in which a potential gradient is provided in the transfer direction. The object of the present invention is to provide a charge transfer device with excellent speed and efficiency and a method for manufacturing the same.

[0014]

[Means for Solving the Problems] The present invention provides a plurality of charge transfer elements, a separation means disposed between the plurality of charge transfer elements, and making only a portion of the plurality of charge transfer elements electrically conductive;
A charge transfer device comprising a plurality of electrodes constituting the charge transfer element, wherein the shapes of the plurality of electrodes, which are overlapped in a non-conducting state, are different at the leading end and the rear end, and the charge transfer direction is wide. It is a transfer device.

The present invention also provides a plurality of charge transfer elements,
a separation means disposed between the plurality of charge transfer elements and making only a portion of the plurality of charge transfer elements conductive; a first electrode disposed on the separation means; and a second electrode constituting the charge transfer element. , having a third electrode, and providing a protrusion extending in the charge transfer direction on one or both of the second and third electrodes on the first electrode to realize overlapping in a non-conductive state. This is a charge transfer device characterized by:

[0016]

[Function] The present invention has a configuration in which a narrow channel effect occurs in the direction of charge transfer between HCCDs due to the configuration of the overlapping and riding portions described above, so a potential gradient is generated within the HCCD and the separation portion, improving charge transfer efficiency. . At the same time, H
There is also a gradient that makes it easier for charges to move in the transfer direction as a CCD. In other words, by intentionally creating a region where the narrow channel effect occurs, a gradient in the transfer direction is created where the potential was previously flat, and the charge transfer efficiency and speed can be significantly improved.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic diagram for explaining one embodiment of the present invention, and will be briefly explained using this diagram. 6 in Figure 2
9 are transfer electrodes, which are made of polysilicon. As shown in FIG. 2, the transfer electrodes 7 and 8 are formed on a silicon substrate via an insulating film (SiO2), so that capacitors C1 and C3 are formed. Note that the transfer electrode 6
, 9 as well. Also, within the silicon substrate,
Since a depletion layer is formed, a capacitor C2 is formed. That is, the transfer electrodes 6 to 9 are connected to the silicon substrate P layer via the capacitors C1 to C3. However, since polysilicon is not a perfect conductor, for example, not all of the lines of electric force from the portion where the transfer electrode 7 rides on the transfer electrode 8 are absorbed by the transfer electrode 8. In other words, some Si
Since it is absorbed by the substrate, a capacitor C4 is equivalently formed. As a result, at the time of CCD transfer, it is necessary to consider the influence of the riding electrode.

FIG. 1 is a partially enlarged view of a charge transfer device according to a first embodiment of the present invention, and this embodiment is used in a region where a narrow channel effect appears. Regarding the transfer between HCCDs, the operation is the same as the conventional one unless otherwise specified.

Reference numerals 1 to 4 indicate transfer electrodes, and reference numeral 5 indicates a separation section. Parts that are unchanged from the conventional example are designated by the same reference numerals. In this embodiment, since the charge storage portion is provided in the transfer electrodes 2 and 4,
Ion implantation is performed under the transfer electrodes 1 and 3 to make the potential shallower than the surrounding area. The difference from the conventional example is the shape of the transfer electrode 3 and the distance between the separation part 5 is large, so the transfer electrode 4 does not ride on the separation part 5 (extension from the HCCD 27).
There is a particular thing.

In this embodiment, the transfer electrode 29 is formed in the first layer of polysilicon, the transfer electrodes 2 and 4 are formed in the second layer, and the transfer electrodes 1 and 4 are formed in the third layer. The transfer electrode 3 is configured to ride on the transfer electrode 4, and the electrode shape is expanded toward the HCCD 28 direction. In the process of transfer between HCCDs, the states φH12, φTG=H, and φH11=L occur. At this time, the influence of the transfer electrode 3 appears below the transfer electrode 4, and the potential of the overlapping portion becomes deeper.

FIG. 3 is a potential distribution diagram in the first embodiment, and the potential distribution will be explained using this diagram.

(a) is a partial extraction of FIG. 1, and (b) to (e) show the potential distribution along aa'. (b) shows the state in which φH11, φH12=H, and φTG=L. In (c), everything is in the H state, so the charge is HCCD
It spreads in 28 directions. φH12, φTG=H, φH11
In case (d) where =L, the transfer electrode 4
The influence of the transfer electrode 3 appears below. In other words, originally,
Charge transfer residuals corresponding to (a) and (c) of FIG. 7 should occur. However, since the transfer electrode 3 is ON, the potential of the portion that overlaps with the transfer electrode 4 is deeper than that of the portion that does not overlap. Furthermore, since the configuration is such that it spreads in the direction of the HCCD 28, a narrow channel effect occurs in which the effect becomes stronger as the overlap increases, so a potential gradient is created in the direction of the transfer electrode 29, and the unevenness of the potential in the conventional method is almost eliminated. Note that since the CCD normally operates at room temperature, it has thermal energy of 25 mV. Further, assuming that the speed of charge follows Maxwell's distribution law, even if the charge remains untransferred, if the unevenness of the potential decreases to about 10 mV, it will overcome this. In other words, if this state (d) is reached, no untransferred data will be generated.

Further, in the same manner as described above, the electrodes riding on the transfer electrodes 29 also act. φH11=L, φH12
=H, a part of the transfer electrode 29 is connected to the transfer electrode 4 (φ
H11), the potential becomes shallow (Figure 3(d)). Figure 1
This corresponds to the upper right triangular part between the separation parts 5 in . Therefore, it is affected by the narrow channel effect, and HCCD2
Potential gradients occur in eight directions.

FIG. 3(e) shows the case where φTG=M (intermediate value). Since the area affected by the narrow channel effect described above is limited, other areas remain flat. Therefore, if the potential instantaneously becomes shallow due to transfer, the charge existing between the separation portions will be distributed to both sides of the HCCDs 27 and 28. To prevent this, the potential of the transfer electrode 29 is changed to a potential deeper than φH11=L by a time T, φTG=M.
It is set to . It is assumed that the applied voltage increases in the order of L<M<H. Regarding φTG=L, a voltage (actually negative) lower than φH11=L is applied to prevent charge from being mixed into the opposite side (HCCD 27) during transfer toward the HCCD amplifier.

FIG. 4 is a partially enlarged view of a charge transfer device according to a second embodiment of the present invention. Figure (a) is “ICD8
9. This is an example in which the present invention is applied between the separation parts described in "1.3 million pixel FIT-CCD for HDTV cameras." 10 to 13, 20 are transfer electrodes, 14 is a separation part, and the charge is indicated by the arrow. The transfer electrode 20 is the first layer, the transfer electrodes 10 and 12 are the second layer, and the transfer electrodes 11 and 13 are
consists of a third layer. Conventionally, a problem occurred when the distance between the separation parts 14 was long, but in the second embodiment,
The transfer electrode 11 on the transfer electrode 20 is characterized by providing a protruding portion. As explained in the first embodiment, φH1=L, φH2
In the =H state, transfer in the direction of the arrow becomes smooth due to the influence of the protrusion, and there is less remaining transfer than in the past.

In this embodiment, the protruding portion is connected to the transfer electrode 11.
However, there is no problem in providing a notch in the transfer electrode 12 or in the transfer electrodes 10 and 11. However, since the φH2 signal is supplied to the transfer electrodes 10 and 11 at the same time, it is only necessary to add a separate signal during transfer between the separation sections 5. In this case, low frequency drive is sufficient, so
This can be easily realized by connecting a switching circuit to the transfer electrode 10 or by switching the power supply of the driver section. For example, a three-value control section of a commercially available VCCD driving IC may be used.

FIG. 2B shows a case where the present invention is applied to a VCCD. 15 to 18 are transfer electrodes, 16 and 18 are the first layer, 15 and 17 are the second layer, and 19 is a channel stopper. When transferring in the direction of the arrow, a potential gradient is generated by the transfer electrodes 15 and 17 formed by riding on each other. As a result, VCCD is less likely to cause unused transfers.
Transfer becomes possible.

Note that the present invention is not limited to the embodiments described above. For example, the spread of the transfer electrodes 3 shown in FIG. 1 may be set on a staircase, or may be arranged symmetrically on the HCCD 28. Alternatively, the transfer electrode 1 may be set. Furthermore, the gist of the present invention is to widen the shape of the overlapping portion of the electrodes in the charge transfer direction. Therefore, a configuration may be adopted in which the electrodes that have ridden are made parallel to the transfer direction and the lower layer electrodes are spread out. others,
It goes without saying that the present invention can be applied to a type of CCD in which a charge storage section is formed by increasing the potential. As described above, various modifications can be made without departing from the gist of the present invention.

[0030]

[Effects of the Invention] As described above, according to the present invention,
When holding a plurality of charge transfer elements, charge transfer between the charge transfer elements can be performed smoothly with a simple configuration, and generation of FPN caused mainly by residual transfer can be prevented. As a result, even if the density increases further in the future, it is possible to alleviate the increase in driving frequency, and it is possible to obtain high image quality without the occurrence of FPN, which is extremely effective in practice.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged view of a charge transfer device in a first embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the same embodiment.

FIG. 3 is a potential distribution diagram in the first embodiment.

FIG. 4 is a partially enlarged view of a charge transfer device in a second embodiment of the present invention.

FIG. 5 is a partially enlarged view of a conventional HCCD.

FIG. 6 is an explanatory diagram of driving pulses.

FIG. 7 is a potential explanatory diagram of a conventional example.

[Explanation of symbols]

Claims (4)

[Claims] 1. A plurality of charge transfer elements, a separation means disposed between the plurality of charge transfer elements for making only a portion of the plurality of charge transfer elements conductive, and a plurality of electrodes constituting the charge transfer elements. In the charge transfer device, the front portion or some of the plurality of electrodes overlap each other in a non-conducting state, and the shape of the overlap has a riding-up portion that expands in the charge transfer direction. Charge transfer device. 2. A first electrode disposed on a separation means, and second and third electrodes forming the charge transfer element,
2. The charge transfer device according to claim 1, wherein the voltage applied to the first transfer electrode is controlled using three or more values. 3. The second and third electrodes are controlled by two values, and one of the voltages applied to the first electrode is set between the two values. Item 2. Charge transfer device according to item 2. 4. A plurality of charge transfer elements, a separation means disposed between the plurality of charge transfer elements for making only a portion of the plurality of charge transfer elements electrically conductive, and a first separation means disposed on the separation means. an electrode, and second and third electrodes constituting the charge transfer element.
In a charge transfer device having an electrode, a protruding portion extending in the charge transfer direction is provided on one or both of the second and third electrodes on the first electrode to form an overlapping and riding portion in a non-conducting state. A charge transfer device characterized by: