JPH0821711B2 - Charge transfer device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a charge transfer device used in a solid-state image pickup device such as a video camera.

(Prior Art) In recent years, a video camera incorporating a solid-state imaging device has been used. The CCD type solid-state imaging device is the mainstream of this solid-state imaging device. A conventional CCD (Charge Coupled Device) has a structure as illustrated in the plan view of FIG. 3 and its BB ′ sectional view (FIG. 4A). As shown in FIG. 3, the transfer channel 1 has a place 1a where the transfer channel width W is narrowed only at one position along the charge transfer direction, and the transfer electrodes 2a, 2b ... A portion 1a where transfer electrodes 3a, 3b, 3c formed of second layer polysilicon are formed so as to cover the edges and the transfer channel width W is narrowed to W '.
The structure is such that the transfer electrode 2a of the first layer is located on the upper side. As shown in FIG. 4A, the transfer electrodes of the first layer and the second layer are each partitioned by a silicon dioxide film (SiO ₂ ) 4 (separated by an insulating layer), and a P-type semiconductor substrate 5 is formed. It is joined to the upper N-type layer 6.

FIGS. 4 (b) and 4 (c) show the potential distribution and the state of the transfer charge C, which correspond in position to FIG. 4 (a).
(B) in FIG. 7 shows where the potential changes in the transfer electrode 2a. This is because the transfer channel 1 shown in FIG. This is because the narrower one has a lower potential. In the drawing, the upper part shows the low potential and the lower part shows the high potential.

Then, in such a state, when the charge is transferred in the direction in which the transfer channel width is narrow as shown in (c), the potential barrier 8 is generated as shown in the drawing, and the transfer charge C is left behind, so that the transfer efficiency is improved. It will be extremely low.

(Problems to be Solved by the Invention) As described above, in the conventional CCD, the width of the transfer channel is narrowed at one position to transfer charges, so that a potential barrier is generated due to the narrow channel effect, and the transfer efficiency is significantly reduced. There was a flaw.

In view of such circumstances, it is an object of the present invention to obtain a charge transfer device having high transfer efficiency by removing the influence of the potential barrier generated by the narrow channel effect.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a transfer channel width narrowed along the charge transfer direction within a predetermined length,
It is characterized in that it is narrowed to a predetermined width at a plurality of locations, and an effective boundary portion of the transfer electrodes is formed on the location where the transfer channel width is narrowed.

(Function) According to the present invention, by narrowing a plurality of points by the above means, a necessary width as a whole is narrowed, and a potential barrier due to a narrow channel effect occurs at a boundary of the transfer electrode at a plurality of points, and the potential barrier of the plurality of points is generated at the time of transfer. By applying different voltages to the transfer electrodes, it is possible to remove the influence of the narrow channel effect, so that high transmission efficiency can be obtained.

(Embodiment) FIG. 1 is a plan view of an embodiment of the present invention, FIG. 2 (a) is a sectional view taken along the line AA 'of FIG. 1, FIG. 2 (b) and FIG. 2 (c).
Shows a potential distribution corresponding to the position in FIG. 2A and a potential distribution when a voltage is applied to the transfer electrodes 3b and 3c.

As shown in FIG. 1 (a), the width W of the transfer channel 1 is narrowed at a plurality of places (1a, 1b, 1c), and the width narrowed at one place is less than or equal to a predetermined width, and as a whole it is necessary. Of the predetermined width W '. And, the places where the width of the transfer channel 1 is narrowed in the narrow places 1a, 1b, 1c and the potential is changed are 7a, 7b, 7c in FIG. 2 (b). The total potential difference due to these potential changes is the same as that in the conventional case (FIG. 4), but the potential difference at one location is much smaller than that in the conventional case. Then, this small potential difference formed in the boundary channel of the transfer electrodes spreads the depletion layer in the channel as shown in FIG. 2 (c) by applying different voltages to the transfer electrodes on both sides during transfer. The potential difference is absorbed and does not serve as a potential barrier. At this time, the transfer electrodes 3b, 3 on both sides
The larger the voltage difference applied to c, the larger the potential barrier can be absorbed. This can increase the width of narrowing the transfer channel at one location.

Here, the narrowing width allowed at one location and the length in the transfer direction of the portion where the width changes are as follows: transfer channel width, concentration and depth of N-type layer 6, thickness of silicon dioxide film 4, difference in applied voltage. Etc.

In addition, although the buried transfer channel is described in this embodiment, the same applies to the surface transfer channel.

(Effect of the Invention) As described above, according to the present invention, the width of the transfer channel of the charge transfer device forms an effective boundary portion of the transfer electrode on the narrowed portion, and is narrowed at one location. The width is set to a predetermined width or less, and the transfer channel width is narrowed at a plurality of points. As a result, a potential barrier due to the narrow channel effect is generated at the boundary between both transfer electrodes, and different voltages are applied to both transfer electrodes during transfer, so that the narrow channel effect is removed and high transfer efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view according to an embodiment of the present invention, and FIG. 2 (a).
Is a sectional view taken along the line AA 'in FIG. 1, FIGS. 2 (b) and 2 (c) are diagrams showing the potential distribution and the transfer state of the transfer charge corresponding to the position in FIG. 2 (a), and FIG. A plan view of the CCD, FIG. 4 (a) is a sectional view taken along line BB ′ in FIG. 3, and FIGS. 4 (b) and 4 (c) are potential distributions corresponding to FIG. 4 (a) and transfer states of transfer charges. FIG. 1 …… Transfer channel, 1a, 1b, 1c …… Narrow space, 2a, 2b, 2c, 3
a, 3b, 3c, 3d …… Transfer electrode, 4 …… Silicon dioxide film, 5
... P-type semiconductor substrate, 6 ... N-type layer, 7,7a, 7b, 7c ... potential change point, 8 ... potential barrier.

Claims (1)

[Claims] 1. A transfer channel width narrowed along a charge transfer direction is narrowed to a predetermined width at a plurality of points within a predetermined length, and an effective boundary portion of a transfer electrode is provided on a portion where the transfer channel width is narrowed. A charge transfer device comprising: