JPS583629B2 - solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device improved so as to make the sensitivity of the end portion of a photosensitive element uniform.

When a one-dimensional sensor with a MOS structure is used for analog applications, uniform sensitivity characteristics are required over all photosensitive elements.

FIG. 1 shows a conventional solid-state imaging device.

This figure shows the end portion of the photosensitive element row as a top view, and for convenience of explanation, only the main parts on one side are shown.

Meandering type channel stops 1 and 1a (hereinafter referred to as charge weirs) are formed on the surface of the semiconductor substrate of the solid-state imaging device, and the impurity concentration of the channel stops is sufficiently higher than that of the substrate, so that the substrate is P-S.
If i, the charge weir is of P+ type.

A photogate electrode 2 (made of polycrystalline silicon, transparent and conductive) is provided on the charge weir via an insulating layer (silicon dioxide).

The photogate electrode 2 extends parallel to the direction of the arrow of the meandering charge weir 1, and its terminal end is formed to sufficiently overlap the charge weir 1a.

An optical slit 3 is provided above the photogate electrode 2 via an insulating layer, and the photosensitive area is determined by the meandering charge weirs 1 and 1a and the optical slit 3.

The width of the optical slit 30 is indicated by W and terminates at point F.

There are charge transfer parts R1 and R2 on both sides of the photosensitive element array.

The channel of the charge transfer section and the photosensitive elements P1, P2...
. . . Pn communicates with each other via open/close electrodes S1 and S2 (transfer gates).

Now, if a positive voltage is applied to the photogate electrode 2, a potential well is generated in the photosensitive elements P1, P2, . . ., Pn.

(However, the opening/closing electrodes S1 and S2 are kept closed).

Next, when light is irradiated, free carriers are generated within the potential well.

After a certain period of time, the opening/closing electrodes S1, S2 are opened, and the photocarriers accumulated in the photosensitive elements P1, P2...Pn are transferred through the opening/closing electrodes S1, S2 (arrows G1, G2...
...Gn and then T1, T2...Tn) to charge transfer sections R1, R2, and charge transfer sections R1, R2.
Lead out by transferring it like an arrow.

The amount of accumulated charge in the above case is proportional to the effective aperture of the photosensitive elements P1, P2, . . ., Pn when the amount of incident light is the same.

The effective aperture of the photosensitive element is determined as follows.

In other words, photocarriers are generated at the meandering charge weir site, and if their free path is λ, then among the photocarriers generated in the meandering charge weir, the photocarriers at a distance from the edge of the photosensitive element to the free path λ of the carriers are Each photosensitive element P1, P2...
...Flows into Pn.

Therefore, the effective aperture of the photosensitive elements Pn, P1, and P2 in the center is equal to the width of each half of the left and right charge weir width J plus the width X of the photosensitive element (Y=1/2J+X+1/2J), and the optical slit width. The product with W is (Y×W).

However, by aligning the end of the optical slit correctly with point C, which is 1/2 J from the left edge of the charge weir 1a that defines the end element, the same effect as the area of the charge weir part has on the effective aperture area of other intermediate elements can be obtained. Since it is difficult to obtain such an optical slit in terms of dimensional accuracy, the charge weir region 1a is widened and the end of the optical slit is terminated at point F with a sufficient margin above the charge weir 1a.

Therefore, the effective aperture of the terminal photosensitive element P3 includes from the edge of the charge weir 1a to point D, which is the sum of the free path λ of the photocarriers described above, and its area is W×(Y-J/2+λ
).

Normally, since J/2<λ, the relative sensitivity of the left and right photosensitive elements is the central photosensitive element P1, P2...
It becomes larger than Pn, and the same effect occurs when the photosensitive area of the terminal photosensitive element becomes larger.

Another way to deal with the above problem is to set the number of elements (for example, 1026) by adding two photosensitive elements to the required number of elements (for example, 1024), and then select point E (approximately the center of photosensitive element P3) in Figure 1. The above problem is solved by terminating the optical slit 3 at the end so that the outputs from the left and right end photosensitive elements (1st and 1026th) are not regarded as signals. 1st and 10th
Since output is also generated from the 26 photosensitive elements, there is a risk of problems in signal processing, and the charge transfer device itself also has problems such as requiring two extra elements.

The present invention provides a novel solid-state imaging device that has been made in view of the above problems.

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

FIG. 2 is a top view showing a main part (one side) of a preferred embodiment of the solid-state imaging device according to the present invention.

In the figure, the same symbols as in FIG. 1 indicate the same functions.

The overflow drain electrode 5 is connected to the terminal 4 via the charge weir C1.

C1 is a charge weir for the overflow channel, 11 is a meandering charge weir, and the charge weir defining the terminal edge of the terminal element also has the same width J as the other inter-element charge weirs, and its terminal end is the charge weir C2 for the overflow channel. connected.

h indicates an overflow channel, and the photogate electrode 2 is formed so as to extend beyond the connection between the end of the meandering charge weir and the charge weir C2 and to be within the overflow channel h.

However, an insulating layer (not shown) is formed between the charge weir and the photogate 2.

An optical slit 3 is formed on the photogate electrode 2 via an insulating layer.

The end point F of the optical slit 3 is formed to be within the overflow channel h.

Therefore, a light receiving section is formed between C and F shown in the figure.

Next, the operation of this embodiment will be explained with reference to FIG.

As explained with reference to FIG. 1, charges are generated in accordance with the amount of light incident on the entire photosensitive element including the left and right end photosensitive elements.

Those charges are transferred to the opening/closing electrodes S1, S2 and the charge transfer part R.
1, lead out through R2.

Here, to explain the reason why the sensitivity of the left and right end photosensitive elements is the same as that of the central part, the width dimension of the charge weir that defines the terminal edge of the end photosensitive element P3 is set to the same width as the charge weir for separation between other elements. In terms of size, each charge weir has the same effect on the effective aperture area of each photosensitive element, and as described above, since the light receiving part Q1 is located within the overflow channel h, the light passing through the optical slit 3 is As a result, the charges generated in the light receiving section Q1 are absorbed by the overflow drain provided in the overflow channel h.

That is, if a reverse bias voltage is applied to the electrode 5, the charges generated in the light receiving section Q1 are absorbed by the overflow drain electrode and discharged to the outside.

This charge therefore never flows into the terminal photosensitive element P3 and therefore does not adversely affect the video signal.

As described above, according to the present invention, the terminal end of the photosensitive element is provided within the overflow channel, so that the charges generated within the channel do not flow into the photosensitive element section.

Therefore, only the required number of bits is required for both the photosensitive element and the readout register.

Furthermore, a uniform video signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a top view of the main part of the end of the photosensitive element part, and FIG. 2 is a top view of the main part including the end of the photosensitive element part according to the present invention. 1, 1a, 11, C1, C2: charge weir, 2: photogate, 3: light shielding film with optical slit, 4: terminal, 5: overflow drain electrode, h: overflow channel, J: meandering that separates each photosensitive element Type charge weir width, P1, P2
...Pn: photosensitive element, W: optical slit width,
Y: Total width including pitch width X and charge weir width J of photosensitive element, Q
1: Light receiving section.

Claims (1)

[Claims] 1 A photosensitive area in which a plurality of photosensitive elements, each of which generates electric charge due to incident light, is arranged in a line through a channel stop for separation between the elements to correspond to the light receiving part of the optical slit, and a photosensitive area that generates electric charge in each photosensitive element. In a solid-state imaging device equipped with a charge transfer unit for extracting charges to the outside as a signal, an overflow is applied to a portion adjacent to the terminal photosensitive element of the photosensitive element row through a channel stop having the same width dimension as the channel stop for separating the elements. 1. A solid-state imaging device, comprising: a channel; the photosensitive region extends onto the overflow channel; and an overflow drain is provided within the overflow channel.