JPH01255273A - Solid-state image sensor - Google Patents

Abstract

PURPOSE:To improve transfer efficiency by constructing at least the width of a charge transfer channel of a vertical transfer unit so as to gradually increase along a charge transferring direction at least under the same electrode. CONSTITUTION:In a solid stage image sensor element in which charges photoelectrically converted by a plurality of regularly arranged photodetectors 2211-2288 are transferred to horizontal transfer units 25a, 25b through vertical transfer units 141a-244b, at least the widths W of the charge transfer channels of the units 241a-244b are so formed as to gradually increase along a charge transferring direction at least under the same electrode. For example, vertical transfer units 241a and 241b, 242a and 242b, 243a and 243b, 244a and 244b are so constructed as to perform a vertical transferring operation by sole gate electrodes. The channel widths W of the units 241a-244b are so formed of a channel stop as to gradually increase its width along the charge transferring direction to the units 25a, 25b.

Description

[Detailed Description of the Invention] [Summary] Regarding a solid-state image sensor that transfers charges using a charge-coupled device, the purpose of improving the transfer efficiency is to perform photoelectric conversion using a plurality of regularly arranged receiving/source parts. In a solid-state imaging device that transfers charges obtained through a vertical transfer section to a horizontal transfer section, at least the width of the charge transfer channel of the vertical transfer section is configured to gradually increase along the charge transfer direction.

[Industrial application field]

The present invention relates to a TG image device, and particularly to a charge coupled device (C
G[): Charge Coupled Dev
The present invention relates to a solid-state image sensor that transfers charges using an ice.

The number of pixels in solid-state image sensors has been increasing in recent years due to the demand for higher image quality, and at the same time, the chip size has been reduced. For this reason, solid 1liil! ! The density of elements has become remarkable, and the unit pixel area (i.e. 1
There is a need to reduce the total area of each part required to generate, accumulate, and transfer charge for a pixel.

However, (in a CD-type solid state image element, each unit pixel has a light receiving section and a transfer section, and in order to improve sensitivity, the area ratio of the light receiving section to the transfer section must be increased. Therefore, even if the unit pixel area is reduced, it is necessary to ensure that a sufficiently large amount of transferred charge can be obtained without deteriorating the sensitivity.

[Conventional technology]

FIG. 5 shows a configuration diagram of an example of a conventional solid-state image sensor. In the same figure, 111 to 1nn are light receiving parts, each consisting of a photodiode, etc., with a total of n pieces in the horizontal direction and n pieces in the vertical direction.
Two light receiving sections are arranged in a matrix. Also,
211-2nn are transfer 1 gates provided in one-to-one correspondence with the light receiving sections 111-'nn, respectively; 31-3. 4 is a vertical transfer section, and 4 is a horizontal transfer section.

Charges obtained by charge conversion by the light receiving sections 111 to 'nn are selected by pixels by the transfer 1 gates 211 to 2nn, and, for example, the N charges from the light receiving sections of nl [l;] of one horizontal line are collectively The data is transferred to the vertical transfer units 31 to 3o.

The charges transferred to the vertical transfer sections 31 to 3o are then transferred in the direction of the arrow (vertical direction) and accumulated in the horizontal transfer section 4.

The horizontal transfer unit 4 transfers this accumulated charge in the direction of arrow B (horizontal direction).
The video signal is transferred serially to the output terminal 6 through the output section 5 and outputted as a video signal. In this way, charges obtained by sequentially selecting pixels from the top to the bottom are transferred to the n light-receiving portion corners of each horizontal line.

In this conventional solid-state WI element, in order to compensate for the decrease in transfer charge due to the reduction in the area of the transfer section (a part of the vertical transfer section corresponding to the transfer gate) due to the reduction in the unit pixel area, vertical direction The gate electrode of the transfer section of the light receiving section constituting several pixels or all pixels in the same vertical direction is shared. Therefore, for example, in the case of a structure in which the gate electrodes of the transfer sections of the light receiving sections of all pixels in the same vertical direction (for example, 1.1, . . . , 1, 1, etc.) are shared, the vertical transfer sections 31 to 31
3n each has a configuration that allows transfer with a single gate electrode.

Thereby, the amount of transferred charges can be the sum of the charges of the plurality of light receiving sections sharing the gate electrode in each of the vertical transfer sections 31 to 3°, so that the amount of transferred charges can be increased.

[Problem to be solved by the invention]

In the conventional solid-state image sensing device described above, as shown in FIG. Accumulated charges 8a from a plurality of pixels are transferred to the transfer section (2) as shown by arrow C as the potential of the transfer section (2) is changed to a low value as shown by 9.

In this case, as shown in FIG. 6 (A>), immediately after the start of transfer, there is a lot of charge in the transfer section (■), and the difference in potential between the transfer sections (■) and (2) is large, so the electric field is large and the charge 8a is The data begins to be transferred to the transfer unit ■ at high speed.

However, since the transfer section (2) shares the gate electrode, the channel ring is good, and as time passes as shown in FIG.
As the charge 8C in the transfer section ■ increases and the difference in potential between the transfer sections ■ and ■ becomes smaller (because the electric field becomes smaller), the charge transfer speed gradually slows down and the normal limited readout time is reduced. Inside, charges are left behind in the transfer section (2), resulting in a decrease in transfer efficiency.

The present invention has been made in view of the above points, and an object of the present invention is to provide a solid-state image sensor that can improve transfer efficiency.

[Means to solve the problem]

In the solid-state imaging device of the present invention, the width of the charge transfer channel of at least the vertical transfer section of the vertical transfer section and the horizontal transfer section is
The structure is such that it gradually becomes wider along the charge transfer direction under at least the same electrode.

(effect) The vertical transfer section and horizontal transfer section are shown in FIG. 1(A).

As schematically shown in (C), the MO8LI structure is formed in which an insulating film 11 is formed on a semiconductor substrate 10 and a gate electrode 12 is further formed thereon, and a channel is formed on the surface side of the semiconductor substrate 10. High concentration diffusion layer 1 called stop
3a and 13b are provided.

By the way, the potential of the semiconductor region corresponding to the channel directly under the gate electrode is as shown in the conceptual diagram of FIG.
The channel width corresponds to the width of the wide gate electrode (19 in Figure 3 (A)) and the narrow gate electrode (20 in Figure 3 (B)), but in principle, as shown by the solid line. The depth is the same.

However, in reality, the edge part of the potential is shown in Figure 3 (
The potential changes not steeply as shown in A) and (B), but gently as shown by the broken line. Therefore, as the channel width becomes narrower, as shown by the broken line in FIG. 3(B), the potential becomes shallower than when the channel width is wide (FIG. 3(A)).

This phenomenon is the same even if the shape of the gate electrode is the same or the channel width is changed using a channel stop. The present invention focuses on this point, and by changing the channel width using a channel stop, the depth of the potential is made to be inclined along the charge transfer direction.

That is, in the present invention, on the upstream side in the charge transfer direction, a high concentration diffusion layer (channel stop) 1 is formed as shown in FIG. 1(C).
3b, the channel width W2 is narrowed to make the potential of the channel width shallow as shown in FIG. 1(D), and on the downstream side of this in the charge transfer direction, high concentration diffusion is made as shown in FIG. 1(A). The channel width W1 is formed relatively wide by the layer (channel stop) 13a, and the potential of the channel width is made relatively deep as shown in FIG. 1(B).

Therefore, the potential of the vertical transfer section in the present invention has a slope that gradually becomes deeper along the charge transfer direction, as shown by 14 in FIGS. 2(A) to 2(C).

As a result, when the potential of the horizontal transfer section to which the charges of the vertical transfer section are transferred is shallow as shown at 168 in FIG. 2(A), the charges 15a accumulated in the vertical transfer section are By making it shallow as shown at 16b in Figure (B), the transfer starts in the direction of the arrow, and even if the charge in the vertical transfer part decreases as time passes as shown at 15b, the potential 14 is tilted. The charge transfer rate continues to be faster than before. Therefore, as shown by 15c in FIG. 2(C), the charge is completely transferred to the horizontal transfer section in a shorter time than in the past.

(Embodiment) Fig. 4 shows a configuration diagram of an embodiment of the present invention.The tree droplet example is a solid-state m-image element consisting of a total of 64 pixels, 8 pixels in the horizontal direction and 8 pixels in the I-direction direction. 2288 is a light receiving part that constitutes each pixel, 23 to 2388 are receiving parts 2211 to 2288
a transfer gate provided corresponding to one body 1;
41. ．． 24B, 242a.

242b, 243a, . . . , 244b are vertical transfer sections, 25a and 25b are horizontal transfer sections, 26a and 26b are output sections, and 27a and 27b are output terminals. The horizontal transfer units 25a and 25b are normally COD.

The vertical transfer sections 241a and 241b are configured to perform a transfer operation using, for example, the same gate electrode, and similarly, the vertical transfer sections 24 and 2425, 243°a and 243b, 244a and 244. are each configured to perform a vertical transfer operation using a single gate electrode.

Further, the channel width W of the vertical transfer section 2418 is configured using the channel stop so that the width becomes gradually wider along the direction of charge transfer to the horizontal transfer section 25a. Similarly, the channel widths of the other vertical transfer sections 241b to 244b are gradually widened along the charge transfer direction. This results in
As described above, each of the vertical transfer sections 241a to 244b has a gradient potential characteristic in which the potential gradually becomes deeper along the charge transfer direction in the region corresponding to its channel.

Note that the vertical transfer unit 241. A total of eight gate towers 244b to 244b may be formed in one-to-one correspondence. In this case, the shape of each single gate electrode corresponds to the channel width of the corresponding vertical transfer section, and the gate electrodes of adjacent vertical transfer sections are separated from each other.

Next, the operation of the above configuration will be explained. Light receiving section 22-2
The light from the subject incident on each of the photodetectors 288 is photoelectrically converted to generate electric charges. On the other hand, the transfer 1 gates 23 to 2388 first transfer charges from the first line of light receiving sections 2211, 2212, 2213°, . . . , 2218 to the vertical transfer section 241a.

24B,, 242a, =..., 244. Selectively transferred to.

Among these, the vertical transfer section 24. 24. 243a and Ia
2a and 244. The charges transferred to the horizontal transfer section 25a are vertically transferred to the vertical transfer section 241. ．． 242°, 243° and 244. The charges transferred to the horizontal transfer section 25b are vertically transferred to the horizontal transfer section 25b.

At this time, as described above, the vertical transfer unit 241. ~244
Since each of b has a gradient potential characteristic, charges are transferred to the horizontal transfer sections 25a and 25b at high speed.

The charges accumulated in the horizontal transfer sections 25a and 25b are serially output as video signals to output terminals 27a and 27b via output sections 26a and 26b.

In the next horizontal scanning period, the light receiving section 2221°2 of the second line
222, 2223. . . , each charge from 2228 is selected and transferred to the vertical transfer units 241a to 244b and the horizontal transfer unit 2.
5a, 25b1 are sequentially outputted to output terminals 27a, 27b through output sections 26a, 26b.

Thereafter, in the same manner as above, the third line, the fourth line, etc.
. . , the 8th line, the 1st line, .

According to this embodiment, the vertical transfer unit 241. Each of ~244b is 1! by a single gate electrode. I! Since the linear cavity is used as an accumulation region for one pixel, the amount of transferred charge can be increased. Moreover, since the channel width is changed to give a slope to the potential, transfer efficiency can be improved. Furthermore, since the vertical transfer directions of the vertical transfer units 241, 244b are reversed for each vertical line, the area can be used effectively.

Note that the present invention is not limited to the above-described embodiments, and can be applied in principle to, for example, a horizontal transfer section, and the widths of the gate electrodes of the vertical transfer section may also be made different. good.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to increase the amount of transferred charge and increase the transfer speed, so even if the unit pixel area decreases due to the increase in the number of pixels, the amount of charge handled does not decrease, and the transfer rate can be increased. It has features such as being able to improve efficiency.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing each part of the structural cross section of the present invention and its potential. Fig. 2 is an explanatory diagram of charge transfer in the solid-state silver image element of the present invention. Fig. 3 is an illustration of the relationship between channel width and potential depth. FIG. 4 is a block diagram of an embodiment of the present invention, FIG. 5 is a block diagram of an example of a conventional solid-state image element, and FIG. 6 is an explanatory diagram of charge transfer in FIG. In the figure, 10 is a semiconductor substrate, 12 is a gate electrode, and 13a and 13b are high 11 degree diffusion layers (channel stop).
, 2211-2288 are light receiving parts, 2311-2288 are transfer gates, 2418,
244b is a vertical transfer section, 25a and 25b are horizontal transfer sections, and 26a and 26b are output sections. (A) (B)÷1 kill t6
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Claims (1)

[Claims] A plurality of regularly arranged light receiving parts (22_1_1 to 2
In a solid-state image sensor that transfers the charges obtained by photoelectric conversion by 2_8_8) to horizontal transfer parts (25a, 25b) via vertical transfer parts (24_1_a to 24_4_b), at least the vertical transfer parts (24_1_a to 24_4_b)
) of the charge transfer channel width (W_1, W_2, W),
1. A solid-state image sensor, characterized in that the device is formed so as to gradually become wider along the charge transfer direction under at least the same electrode.