JPS5933864A - Color solid stage image pickup element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Object of the Invention] The present invention provides a photoelectric conversion element for extracting a plurality of color signals on a semiconductor substrate, and a scanning element (COD shift register) for extracting optical information from each photoelectric conversion element. Multiplicated C
The present invention relates to a CD-type color solid-state image sensor.

(Prior art) A solid-state image sensor requires an image sensor plate with the resolving power of an imaging electron tube used in current television broadcasting. Therefore, the solid-state imaging device is manufactured using MO8 large-scale integrated circuit technology, which allows for relatively easy integration.
Generally, a C0D (optical diode + MOS shift register) or a MOS) run lister (optical z-diode + MOS shift register) is used as a component.

FIG. 1 shows the basic configuration of a conventional CCD type solid-state imaging device, which is characterized by low noise.

Reference numeral 1 denotes a photoelectric conversion element made of, for example, a photodiode, and 2 and 3 denote a vertical CCD shift register and a horizontal shift register for taking out optical signals accumulated in the photoelectric conversion element to output terminals.

When constructing a color television camera using the solid-state image pickup device shown in FIG. 1, three image pickup plates are generally required to convert each of the red, edge, and blue lights into electrical signals. However, color cameras that use three solid-state image pickup plates require a color separation optical system to separate the subject into the three primary colors of red, green, and blue.
This requires a special imaging lens, which poses a major obstacle to making cameras smaller and cheaper.

Therefore, as an example shown in FIG. 2, color filters 4 (R) and 5 (G) are arranged in a checkered pattern and transmit only red (It), green (G), and blue (B) light.

6(B), a method was proposed for extracting the three primary color signals from one imaging plate by associating each photoelectric conversion element constituting the imaging pixel matrix (Japanese Unexamined Patent Application Publication No. 1983-1999).
(See Publication No. 112228). The color filter of that configuration is
The peripheral filters (G) are arranged horizontally and vertically on the image pickup plate, filling the gaps between the red (几) and blue (B) color filters, so even when the number of pixels on the solid-state image pickup plate is small. , it is possible to obtain a color solid-state image pickup device with little deterioration in resolution, and it is an extremely excellent method for extracting color signals from a single image pickup plate.

Therefore, if this method (a method for extracting color signals from a single image pickup plate) can be applied to the above-mentioned CCD type image pickup device, it will be possible to realize extremely high image quality in a solid-state device.

However, if this method is directly applied to a conventional CCD type image sensor, the shift direction of the CCD is specified in one direction, so in the process of transferring color signal charges,
The color signal charges of the previous field and those of the subsequent field overlap, resulting in a decrease in resolution and the occurrence of an afterimage.

Therefore, we considered a configuration shown in FIG. 3 as a specific configuration when this method is combined with CCDW imaging. That is, gates for sending signal charges to the vertical COD shift register are provided in a checkerboard pattern, and the vertical CCD shift register) L
/The center of the register is separated by an insulator, and the C
An OD 凰 image sensor was constructed.

(6-1, 6-2) and (6-3, 6-4) are vertical COD shift registers running in the vertical direction, 7-1, 7-2
, 7-3, and 7-4 are photoelectric conversion elements arranged in a matrix (checkerboard pattern), and 8-1, 8-2, and 8-3 are horizontal COD shift registers running in the horizontal direction. Here, in the center of a pair of vertical CCD shift registers, both (
A separation strip 11 is provided to electrically insulate the load transfer channel). Further, arrow 9 indicates a gate through which the charges accumulated in the photoelectric conversion element are sent to the vertical COD shift register.

There are two types of color filters: a three-primary-color type (red, green, W color) and a complementary-color filter.Here, the three-primary color type shown in FIG. 2 will be explained as an example.

Considering the case where 7-1 and 7-4 correspond to green, 7-2 corresponds to red, and 7-3 corresponds to blue, the vertical COD shift register (6-2, 6-4) has a green signal charge. , red charges are sent to register 6-1 and blue charges are sent to register 6-3, and are transferred in the vertical direction shown by arrow 10, and these signal charges are further transferred to a transfer gate (not shown).
The horizontal 〇CD shift)L/register is sent through the register.

As a result, horizontal COD shift registers 8-1.8-2.
Output 12-1.12-2゜12- provided at one end of 8-3
From 3, green, red, and green signals can be obtained respectively.

In Figure 3, three horizontal COD shift registers are provided, but since the sampling period for red and evening (the interval when continuous signals are extracted at regular intervals) is half of the edge, the red and blue Signal charges may be transferred in the same horizontal CCD shift register. In this case, only two horizontal C0D7 floor stars are required. In addition, when there are four types of color filters, four horizontal CCf) shift) l/registers may be provided for each color. Therefore, the number of horizontal COD shift registers may be selected to any number greater than or equal to two.

As mentioned above, the COD type color image sensor has the advantage that it does not generate field afterimages because it is capable of interlaced scanning in which two columns in the vertical direction are simultaneously read out. Therefore, it is possible to obtain extremely high image quality for a solid-state device.

However, when arranging two vertical COD shift registers as in the configuration shown in FIG.
The maximum amount of charge that can be transferred is the same as that of the conventional configuration (first
In the case of (Fig.), it is smaller than about S (two registers are arranged and a separator is required between the two registers). This means dynamic range (ratio of saturated light amount to noise), blooming (when more light than saturated light amount is incident,
8N for dark current (a phenomenon that occurs when excess charge generated in the photoelectric conversion unit flows into adjacent pixels and vertical transfer units)
This is a major disadvantage that offsets the above-mentioned advantages.

Purpose of the Invention The purpose of the present invention is, in order to improve the above-mentioned drawbacks, to make it possible to extract three primary colors from a single imaging plate without reducing the dynamic range with respect to the amount of light, the blooming suppression rate, and the S/N ratio with respect to dark current. An object of the present invention is to provide an fcCCD type color image sensor.

(Detailed Description of the Invention) In order to achieve the above object, the present invention is configured as follows.That is, a group of photoelectric conversion elements for extracting color information and optical information on the same semiconductor substrate, and a group of photoelectric conversion elements for extracting color information and optical information on the same semiconductor substrate, and a group of photoelectric conversion elements for extracting color information and optical information on the same semiconductor substrate. A collar that integrates a set of electrically isolated vertical COD shift registers facing each other that sequentially transfers signal charges, and a horizontal COD shift register group that receives and receives signals transferred from the vertical COD shift registers. In the solid-state imaging chain, the storage capacity of the vertical COD shift register (
In other words, in order not to reduce the maximum amount of charge that can be transferred, the vertical COD to which the photoelectric conversion element group with high photosensitivity (that is, has more optical signal charges) belongs
Increase the transfer charge capacity of the shift register group, and increase the transfer charge capacity of the horizontal COD shift register that receives and takes this transfer charge.
By reducing the transfer charge capacity of the vertical COD shift register group to which the photoelectric conversion element group (with less optical signal charge) belongs, and by reducing the transfer charge capacity of the horizontal COD shift register which receives this transfer charge. There are signs.

(Embodiments of the invention) Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 4 is a diagram showing the configuration of a COD white color solid-state image sensor, which is the gist of the present invention. 13-1.

13-2.13-3.13-4 is a vertical COD shift register, and 14 is an insulating separation band.

(9) As can be seen from FIG. 4, since the separation strip 14 is formed on the left side of the center (located at the center in FIG. 3), the vertical COD shift register 13-2.1
3-4 is a vertical COD shift register 13-1.13-
The amount of signal charge that can be transferred (that is, the maximum storage capacity) is larger than that of No. 3.

Photoelectric conversion element (generally a photodiode) 7-1゜7-2.
7-3.7-4, the amount of optical signal charge accumulated in one field period due to light incidence is determined by the spectral sensitivity of the photodiode,
The color temperature of each photodiode varies depending on the type of color filter placed above the photodiode and the color temperature of the illumination light source used.

In other words, this means that the effective sensitivity of each photodiode is different, and a photodiode with higher sensitivity accumulates a larger amount of signal charge.

In this embodiment, the sensitivity of the photodiode 7-1, 7-4 is 7-
This is an example assuming a larger case than 2.7-3, and the charge of the diode 7-1 and 7-4, which has a large amount of accumulated charge, is transferred to the vertical (10) CC1) shift register 3-, which has a large transfer charge capacity. 213-4, - diode 7-2 with a small amount of force storage charge. 'The charge of I-3 is transferred to the vertical COD shift register 3, which has a small transfer charge capacity.
-1.Sent to 13-3.

In this figure, where to form the insulation portion M is determined by photodiode 7-1 (or 7-4) and photodiode 7-2 (
Alternatively, it may be determined according to the effective sensitivity ratio of 7-3). For example, if the effective sensitivity ratio of both diodes is 2:1, the width dimension d2 of the vertical COD shift register 3-2 (13-4) and Vertical CCD shift register 3-1 (la-3
) may be set to 2=1. Also,
In this example, it is assumed that the effective sensitivities of photodiodes 7-1 and 7-4 are equal, and that the effective sensitivities of photodiodes 7-2 and 7-3 are equal, but in reality, there is a difference between these photodiodes. In many cases, the effective sensitivity is different for each. In this case, assuming that the effective sensitivity of each photodiode is, for example, 7-1) 7-2) 7-3) 7-4 in descending order, the charges of the top two photodiodes 7-1 and 7-2 are (11) Transfer charge ilF! Top two vertical CCJs with large F valleys
) Transfer by shift register 13-2.13-4, lower 2
Transferring the charges of the two photodiodes 7-3 and 7-4 The lower two vertical COD shift registers 13 with small charge capacity
The vertical COD shift register and photodiodes may be arranged so as to transfer data at -1.13-3.

Furthermore, if it is desired that the storage capacitance of the vertical COD shift register corresponds completely to the effective sensitivity of the photodiode, the transfer charge capacity of the four vertical COD shift registers may be changed for each of the four vertical COD shift registers. Figure 4(b) shows the width of the vertical COD shift register using a CCD type device constructed under the assumption that the effective sensitivity of the photodiode is 7-1>7-4>7-3>7-2. d4)d so that the dimensions dl・d2 + d3 + d4 respectively correspond to the effective sensitivity of each photodiode.
2) The insulating separation band 14 is formed under the condition that dH>d3.

FIG. 5 is a diagram showing the element structure of the embodiment shown in FIG. 4 described above. The same figure (a) shows the insulating isolation band 14 (12) and the thick insulating oxide film 14a (generally SiO2 is used).
In this case, the same figure (b) shows the case where the insulating separation band is formed of the same material as the substrate and the highly concentrated impurity layer 14b (Here, two picture elements necessary for the explanation are described). . 15 is, for example, a pm semiconductor substrate, 7' (
7'-3, 7'-4) are photodiodes made of n-type impurities, for example.

16 is a pair of opposing vertical COD shift registers 13'
17-1 and 17-2 are two-layer electrodes made of polycrystalline silicon, for example, which constitute a vertical COD shift register. 18 is a low-concentration nya impurity layer provided to make the vertical CCD shift register into an embedded board (no grain is required if it is a surface type), 19 is a gate oxide film that insulates the electrode and the substrate, and 20 is a Photodiode 7'-3,7'
This is a transfer gate region for transmitting the signal electrodes accumulated at -4 to the vertical COD shift registers 13'-3 and 13'-4.

Normally, the dimensions of the electrodes (17-1 or 17-2) in the transfer direction (13) (perpendicular to the plane of the paper) are the same since the vertical COD shift registers 13'-3 and 13'-4 use the same electrodes. Therefore, both vertical C
The signal storage capacitance ratio of the OD shift registers 13'-3 and 13'-4 is determined by the ratio of the electrode widths d1 to d2.

In the above embodiment, it is assumed that the electrode widths W of the horizontal COD shift registers arranged in a plurality of columns are the same. This is because the Mizuko CD shift register placed at the end of the vertical CCD shift register has more leeway in terms of layout dimensions than the vertical CCD shift register placed two-dimensionally.For example, each horizontal COD shift register This is because both can have a storage capacitance greater than the amount of signal charge accumulated by the photodiode with maximum sensitivity.

However, if the chip size is to be reduced in the future, the horizontal COD shift registers may also each have a storage capacity corresponding to the amount of signal charge transferred. FIG. 6(a) shows three columns of horizontal COD shift registers 8'-1, 8'-2.
,8'-3 have different storage (14) capacitances (electrode widths W1, W2, W3),
Horizontal COD shift register 8'- with the largest storage capacity
3 indicates transferring the signal charge of the photodiode with maximum sensitivity. FIG. 5B corresponds to the case where the color filter is a four-color filter, and the horizontal COD shift register 8'-4 having the largest storage capacity transfers the signal charge of the photodiode having the maximum sensitivity. Here, if the effective sensitivities of the photodiodes that handle two of the four colors are equal, for example, two of the four horizontal COD shift registers,
For example, the electrode widths W2 and W3 of 8'-2 and 8'-3 may be made the same dimension (W2-W3).

The above explanation has been made with reference to the interline type, which has a high degree of integration among CCD type image sensors, but it may also be applied to the frame transfer type, which is another type, without departing from the spirit of the present invention. , it is obvious that the present invention can be applied.

Furthermore, the present invention can be applied as is to a two-story image sensor using a photoconductive thin film as a photoelectric conversion element instead of the above-mentioned photodiode; (15) In this case, the above-mentioned In each embodiment, the photodiode may be replaced by a photoconductive thin film element.

Further, in each of the above embodiments, it is assumed that the color filter is in a mosaic shape (dot shape), but in the case of a stripe shape, a configuration as shown in FIG. 7 may be used. The structure of the CCD type image sensor for the striped image is similar to the conventional one as shown in FIG. As mentioned above, the conventional configuration has problems such as reduced resolution and generation of afterimages, and cannot be said to be a desirable configuration.However, the present invention has the advantages of (1) improvement of the dynamic range of the element, and (2) blooming. Advantages such as improved suppression rate and (3) reduced dark current can be utilized as is.

Here, 2-1, 2-2, 2-3 are each diode 1-
1.1-2.1-3 are vertical CCD shift registers with different storage capacities depending on the effective sensitivity; 3 is a horizontal CCD shift register; color signals are taken out in time order from the same vertical shift register; There is no need to arrange multiple rows of horizontal COD shift registers, and the storage capacity of the shift registers (16) may be designed to have a storage capacity greater than the maximum effective sensitivity of the photodiodes.

Although the present invention has been explained in detail using examples above,
Furthermore, the present invention will be effective in reducing the chip size in the future, and by applying a desired layout design to the electrode pattern, it can be manufactured in exactly the same process steps as conventional CCD type elements. This has the great advantage of being able to do this, and there is no problem of reduced manufacturing yield.

[Effects of the Invention] As detailed above, in the CCD type image sensor of the present invention, the charge storage provided in the vertical COD shift register and the horizontal COD shift register that transfer the signal charges accumulated by each photoelectric conversion element is By setting the capacitance to a value that corresponds to the effective sensitivity (i.e., accumulated charge) of the photodiode to which each resistor belongs, it is possible to improve the dynamic range of the element, improve the pluming suppression rate, and increase unnecessary dark current. This can be achieved by extracting 3yX colors from a single image pickup plate (17) while reducing the SN ratio due to the suppression function.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional CCD type solid-state image sensor.
Fig. 2 is a diagram showing the arrangement of color filters used for colorizing the imaging probe, which is a conventional technique, and Fig. 3 is a diagram showing the arrangement of a CCD solid-state image sensor, which is an improved version of Fig. 1 in order to apply Fig. 2. FIG. 4 is a diagram showing the configuration of a CCD solid-state image sensor according to an embodiment of the present invention, FIG. 5 is a diagram showing the internal structure of the CCD solid-state image sensor according to the present invention, FIG. FIG. 7 is a diagram showing the configuration of an embodiment different from the embodiment described above. 1.7...Photoelectric conversion element, 2.13...Vertical CCD
Shift register, 3, 8... Horizontal CCD shift register, 4, 5.6... Color filter, 9.10... Arrow indicating transfer direction, 11.14... Insulating separation band, 12.
...Output of horizontal CCD shift register, 15...Semiconductor substrate, 16...Vertical CCD shift register area, 1
7... CCD electrode, 18... Low concentration impurity, 19.
...Gate oxide film, 20...Transfer gate region, d...
・Vertical (18) Width of COD electrodes configuring COD shift register, W・
...The width of the COD electrode that constitutes the horizontal CCD shift register. Agent Patent attorney Toshiyuki Usuda (19) High 1 口■ 2 Figure 6F Kanguchi 口■■口口口口口口

Claims (1)

[Claims] 18 A group of photoelectric conversion elements for extracting color information and optical information on the same semiconductor substrate, a set of electrically insulated vertically facing each other for sequentially transferring optical signal charges accumulated in the elements. In a color solid-state image sensor that integrates a COD shift register group and a horizontal COD shift register group that receives and receives signal charges transferred from the vertical COD shift register, the vertical COD to which the photoelectric conversion element group with a large amount of signal charge belongs
A color solid-state image sensor characterized in that the allowable transfer charge amount of a shift register group is increased, and the allowable transfer charge amount of a vertical COD shift register group to which a photoelectric conversion element group with a small amount of signal charge belongs is reduced. 2. Increase the transfer charge capacity of the horizontal COD shift register that receives the transfer charge of the vertical COD shift register group, which has a large transfer charge capacity, and accepts the transfer charge of the vertical CCD shift register group, which has a small transfer charge capacity. Take horizontal CO
2. The color solid-state image sensor according to claim 1, wherein the transfer charge capacity of the D shift register is reduced.