JP2762059B2 - CCD solid-state imaging device and signal processing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CCD solid-state image pickup device, and more particularly to a CCD solid-state image pickup device in which sensitivity is improved by detecting a signal using electrons and holes and a dynamic range with respect to illuminance is increased. It relates to the signal processing method.

[0002]

2. Description of the Related Art An ordinary CCD solid-state image pickup device selects only one of a pair of electrons and holes generated by incident light as a signal charge, stores and transfers the signal charge, and performs signal processing.
Unselected signal charges were removed as unnecessary charges. Since the mobility of electrons is larger than the mobility of holes, electrons are usually selected as signal charges.

FIG. 1 is a block diagram of a conventional frame transfer type CCD solid-state imaging device. Frame transfer C of FIG.
The CD solid-state imaging device includes a light receiving region 11 for generating a signal charge for incident light, a storage region 12 for storing the signal charge from the light receiving region 11 for a certain period of time, and one line of the signal charge stored in the storage region 12. HCCD 13 that extracts each time,
And a charge detection and amplification circuit 14 for detecting and amplifying signal charges output from the HCCD 13.

In the CCD solid-state image pickup device of the frame transfer system, the light receiving region 11 generates signal charges for incident light, and accumulates the generated signal charges for a certain period of time. The signal charges accumulated in the light receiving region 11 are temporarily transferred to and accumulated in the accumulation region 12 during the vertical erasing period, and the signal charges accumulated in the accumulation region 12 are extracted line by line until the next vertical erasing period. To the HCCD 13. Storage area 12
When all the signal charges accumulated in the light receiving area are extracted, the signal charges generated and accumulated in the light receiving area during that time are further moved to the accumulation area and the above operation is repeated. Here, since electrons are used as signal charges, an electronic signal detection and amplification circuit is used as the detection and amplification circuit 14.

FIG. 2 shows a sectional structure of the frame transfer type CCD solid-state imaging device of FIG. FIG. 2 shows only the cross-sectional structure of the conventional frame transfer type CCD solid-state imaging device with respect to the storage region 12, but the light receiving region 11 and the storage region 12 have substantially the same cross-sectional structure. However, a light-shielding film made of aluminum for blocking incident light and a transfer electrode are formed on the accumulation region, but the light-shielding film and the transfer electrode are formed on a light-receiving region for generating signal charges for the incident light. Is not formed.

Referring to FIG. 2, a conventional frame transfer CCD
The structure of the n ⁻ type substrate 12
1 and a p ^- type well 122 formed on the substrate 121.
And an n-type buried channel region 123 formed in the well 122, a channel stop region 124 formed in contact with the n-type buried channel region 123 in the p ⁻ -type well 122, and formed on the surfaces thereof. It can be seen that it is composed of an insulating film 125 made of SiO ₂ and a transfer electrode 126 formed on the insulating film 125.

FIGS. 3A and 3B show 2A-2A 'of FIG.
3B and 2B-2B ', and FIG.
(C) shows the potential distribution on the lines 2A-2A 'and 2B-2B' in FIG.

Of the signal charges generated from the light receiving region 11 by the incident light, electrons are accumulated in the n-type buried channel region 123 of the accumulation region 12 as shown by a line 132 in FIG. 3 substrate 121 and the insulating film 125 as appearing on line 131 of (C), i.e. Si / SiO ₂ near the interface and p ^- periphery gathered type well 122 to the p ⁺ -type channel stop region 124 via respective Removed. As described above, in the conventional CCD solid-state imaging device, the holes are processed as unnecessary signal charges, and no consideration is given except for removing the holes quickly so as not to adversely affect the electron transfer.

FIG. 4 is a graph showing the photoelectric conversion characteristics of a conventional CCD solid-state imaging device. The X-axis represents the illuminance of the CDD surface due to incident light, and the Y-axis represents the output voltage of the CCD. Usually, the dynamic range of a CCD is defined by a linear region where the illuminance and the output voltage are proportional. Further, the sensitivity of the solid-state imaging device can be represented by a slope (mV / Lux) in this linear region. Therefore, as shown in FIG. 4, in the solid-state imaging device having the sensitivity characteristic indicated by A and the solid-state imaging device having the sensitivity characteristic indicated by B, A has a sensitivity about twice higher than B. I have. However, in the case of a dynamic range related to illuminance, B has a wider dynamic range than A. If A wants to maintain the same dynamic range as B, the maximum output voltage of A must be twice that of B. However, there are limitations on the drive voltage of the CCD, the input voltage of the video signal processing IC, and the like, so that it is not easy in practice.

[0010]

Even if there is a photosensitivity charge detection technique that is ten times or more than the conventional technique, there is a problem of the dynamic range with respect to the illuminance as described above when using this technique. In other words, the above-described high-sensitivity charge detection technique is useful at very low illuminance, but at a high sensitivity, it is more than a certain level in a case where bright and dark subjects are mixed, or in a scene such as outdoors in a very bright daytime. The portion having brightness becomes completely white, and the shade cannot be distinguished. Incidentally, it is theoretically and practically impossible to increase the maximum output voltage by a factor of ten and to match all the drive voltages and signal processing circuits. Accordingly, there is a need for a solid-state imaging device capable of detecting and amplifying charges with low sensitivity in a low illuminance area and low sensitivity in a high illuminance area even within the same screen.

The present invention has been made to solve the above problems, and has as its object to provide a CCD solid-state imaging device capable of detecting a signal with high sensitivity in a low illuminance region and low sensitivity in a high illuminance region, and a signal processing method therefor. Is to provide. It is another object of the present invention to provide a CCD solid-state imaging device that achieves both high sensitivity and a wide dynamic range for illuminance, and a signal processing method thereof.

[0012]

According to the present invention, there is provided a light receiving region for generating a signal charge with respect to incident light, a storage region for storing a signal charge from the light receiving region for a predetermined time, An HCCD that extracts the signal charges accumulated in the area line by line, a signal charge detection and amplification circuit for high sensitivity that detects and amplifies the signal charges for electrons among the signal charges output from the HCCD, and an output signal from the HCCD. Including a low-sensitivity signal charge detection and amplification circuit that detects and amplifies signal charges for holes among the signal charges
A feature is to provide a D solid-state imaging device.

The light-receiving region and the storage region of the solid-state imaging device according to the present invention include a low-concentration substrate of a first conductivity type, a well of a second conductivity type formed on the substrate, and a first conductivity type formed in the well. A first impurity region having a first conductivity type, a second impurity region having a second conductivity type formed on a surface of the first impurity region, and a first impurity region formed in the well in contact with the first and second impurity regions. A third impurity region having a conductivity type;
A fourth impurity region having a high concentration of the second conductivity type formed in the well in contact with the impurity region.

According to the method of the present invention, signal charges of electrons and holes are generated for incident light, the generated signal charges are stored for a predetermined time, and the stored signal charges are extracted line by line. Detecting a signal charge for electrons among signal charges extracted line by line, detecting signal charges for holes among signal charges extracted line by line, and detecting a signal for electrons. Combining and outputting a detection signal for the hole.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 shows a configuration of a CCD solid-state imaging device according to an embodiment of the present invention. According to FIG. 5, the frame transfer C according to the embodiment of the present invention is performed.
The CD solid-state imaging device includes a light receiving region 51 that generates signal charges for incident light, a storage region 52 that stores the signal charges from the light receiving region 51 for a certain period of time, and one line of the signal charges stored in the storage region 52. HCCD 53 that extracts
Among the signal charges output from the CCD 53, a high-sensitivity signal charge detection and amplification circuit 54 that detects and amplifies signal charges for electrons, and among the signal charges output from the HCCD 53, detects and amplifies signal charges for holes. And a signal charge detection and amplification circuit 55 for low sensitivity.

In the frame transfer type CCD solid-state imaging device of the present invention having a structure as shown in FIG.
Numeral 1 generates signal charges, that is, electrons and holes, with respect to incident light, and accumulates the generated signal charges for a certain period of time. The signal charges accumulated in the light receiving region 51 are transferred to and accumulated in the accumulation region 52 during the vertical erase period. Storage area 52
The signal charges stored in the line are extracted line by line until the next vertical erasing period and transferred to the HCCD 53. When all the signal charges accumulated in the accumulation region 12 are extracted,
Meanwhile, the signal charges generated and accumulated in the light receiving region further move to the accumulation region, and the above operation is repeated. on the other hand,
Of the signal charges transferred to the HCCD 53, electrons are detected and signal-processed by the high-sensitivity signal charge detection and amplification circuit 54, and holes are formed in the low-sensitivity signal charge detection and amplification circuit 5.
The signal is detected and processed at 5.

FIG. 6 is a sectional structural view of the storage area 52 of the frame transfer type CCD solid-state imaging device of FIG.
(A) is a structural view of a cross section perpendicular to the direction in which signal charges are transferred, and (B) is a structural view of a cross section parallel to the direction in which signal charges are transferred. FIG. 6 shows only the sectional structure of the storage region 52 of the frame transfer type CCD solid-state imaging device according to the embodiment of the present invention, but the light receiving region 51 and the storage region 52 have substantially the same sectional structure. However, an aluminum light-shielding film and a transfer electrode for blocking incident light are formed on the accumulation region, whereas the light-shielding film and the transfer electrode are formed on a light-receiving region that generates signal charges for the incident light. No electrodes are formed.

Referring to FIG. 6, a storage area 52 of a frame transfer type CCD solid-state imaging device according to an embodiment of the present invention.
Are composed of an n ⁻ type substrate 521 and an n ⁻ type substrate 52.
1 and a p ^- type well 522 and a p ^- type well 5
22, a first n-type region 523 acting as a buried channel region for electrons, and a first n-type region 523
A p-type region 524 formed as a buried channel region for holes formed in the surface of the first n-type region 52;
A second n-type region 525 which serves as a channel stop region for holes formed in contact with the p-type region 524 on both sides thereof and serves as a buried channel region for electrons; p acting as a drain region for the channel stop region and the hole for the formed type well 522 electronic ^{+ -} p contact 525
It comprises a mold region 526, an insulating film 527 made of SiO ₂ formed on the substrate, and a transfer electrode 528 formed on the insulating film 527. Although not shown in FIG. 6, a light-shielding film is formed on the transfer electrode 528.

FIGS. 7A and 7B show 5A-5A 'of FIG.
2 shows a cross-sectional structure and a band diagram along a line, respectively. A buried channel of electrons is formed in the conduction band, and a buried channel of holes is formed in the valence band.

FIGS. 8A and 8B show 5A of FIG. 6A.
-5A 'and 5B-5B' show a cross-sectional structure along the line,
FIG. 8 (C) shows 5A-5A 'and 5B-5 of FIG. 6 (A).
4 shows a profile of a conduction band at a line B ′. Of the signal electrons generated by the incident light, the electrons are accumulated in the first n-type region 523 acting as a buried channel region for electrons, as shown by lines 531 and 532 in FIG. When excess electrons are generated in excess of the capacity of the first n-type region 523, the excess electrons overflow the potential barrier of the p ⁻ -type well 522 and flow out to the n ⁻ -type substrate 521. Therefore, the solid-state imaging device of the present invention has a vertical overflow drain structure for electrons.

FIGS. 9 (A) and 9 (B) show 5A-A in FIG. 6 (A).
FIG. 9C is a sectional view taken along line 5A 'and 5B-5B', and FIG. 9C is a sectional view taken along lines 5A-5A 'and 5B-5B' in FIG.
2 shows a profile of a valence band in a line. Referring to FIG. 9, it can be seen that the second n-type region 525 acts as a channel stop region for holes and the p-type region 524 acts as a buried channel region for holes.

FIG. 10A shows 5C-5C 'of FIG. 6A.
FIG. 10B shows a cross-sectional structure taken along a line, and FIG.
3 shows a valence band profile at the 5C-5C ′ line of FIG. By appropriately adjusting the applied voltage to the transfer electrode 528, the substrate 521, and the like, as shown in FIG. 10B, 5C of FIG.
A valence band profile at the -5C 'line is obtained. Of the signal charges generated by the incident light, holes are accumulated in the p-type region 524 acting as a hole buried channel region as shown in FIG. The p ⁺ type region 526 acts as a horizontal overflow drain for holes. Therefore, during the period of insensitivity to electrons, n
^- applying a sufficiently large positive voltage to the mold substrate 521. During this period, no electrons are accumulated in the first n-type region 523 due to the positive voltage applied to the n ⁻ -type substrate 521. Therefore,
The first n-type region 523 does not function as a buried channel region for electrons. Therefore, during the period of insensitivity to electrons, all the electrons generated by the incident light are not accumulated in the first n-type region 523 but are swept out to the n ⁻ -type substrate 521. On the other hand, a negative voltage is applied to the transfer electrode 528 during the period of insensitivity to holes. During this period, no holes are accumulated in the p-type region 524 due to the negative voltage applied to the transfer electrode. Therefore, p-type region 254 does not function as a buried channel region for holes. Therefore, during the period of insensitivity to holes, all holes generated by incident light are not accumulated in the p-type region 524 but are swept out through the p ⁺ -type region 526.

Hereinafter, the transfer of charges will be described. The CCD solid-state imaging device of the present invention is applicable to both the four-phase drive system and the two-phase drive system. FIGS. 11A to 11D show waveform diagrams of the four-phase driving clock pulse, and FIGS.
(H) shows the potential distribution of the channel region for each period.
As shown in FIG. 12, in the case of the CCD solid-state imaging device of the present invention employing the four-phase driving method, the electrons 551 and the holes 5
52 are transferred in the same direction.

FIGS. 13A and 13B show waveform diagrams of two-phase driving clock pulses, and FIGS. 14A to 14D show potential distributions in the channel region for each period. As shown in FIG. 14, in the case of the CCD solid-state imaging device of the present invention employing the two-phase driving method, electrons 551 and holes 552 are transferred in directions opposite to each other. As described above, the two-phase driving method makes it possible to separate electrons and holes by using the characteristic that the transfer directions of electrons and holes are reversed.

As described above, since the CCD image element of the present invention utilizes not only electrons but also holes as signal charges, the signal charges are increased almost twice as much as in the prior art, and the sensitivity is greatly improved. That is, by setting the sensitivity of the signal charge detection and amplification circuit to high sensitivity for electronic and to low sensitivity for hall, and switching between two kinds of signal charges, it is possible to cope with both high illuminance shooting and low illuminance shooting. A CCD camera can be realized. If the sensitivity of the signal charge detection and amplification circuit is set to high sensitivity for electronic and low sensitivity for hall, and two types of signals for the same screen are synthesized by an analog / digital converter and a digital signal processor,
It is possible to obtain a high-sensitivity image with a wide dynamic range with respect to the illuminance than before.

Next, a description will be given using the photoelectric conversion characteristics of the CCD solid-state imaging device shown in FIG. For example, A and B are output sensitivity characteristics for an electron signal and output sensitivity characteristics for a hole, respectively, and a combined sensitivity characteristic is defined as C = A + B. In this case, in the low illuminance region, a value obtained by adding the output sensitivity to the low-sensitivity Hall signal to the output sensitivity to the high-sensitivity electronic signal becomes a new sensitivity of the solid-state imaging device according to the present invention. Therefore, the solid-state imaging device of the present invention can provide a slightly higher sensitivity than the conventional case where only the output sensitivity to an electronic signal is used. In the high illuminance region, the output sensitivity to the electronic signal is saturated, so that the output sensitivity to the hall signal for low sensitivity can be obtained. Therefore, the solid-state imaging device of the present invention can realize a dynamic range for illuminance that is twice or more as wide as that of a conventional solid-state imaging device using only output sensitivity to an electronic signal.

[0027]

According to the present invention, by simultaneously outputting electrons and holes as signal charges, a CCD solid-state imaging device is provided for imaging a low illuminance region with high sensitivity and a high illuminance region with low sensitivity for the same screen. An element can be realized. In the solid-state imaging device according to the present invention, in which all electrons and holes are used as signal charges, by adding a hole signal to an electronic signal, the signal amount increases and the sensitivity of the device improves. Further, by connecting a signal charge detection and amplification circuit having different sensitivities to electrons and holes and detecting electrons and hole signals simultaneously, the dynamic range with respect to incident light can be expanded and the sensitivity of the element can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional frame transfer type CCD solid-state imaging device.

FIG. 2 is a sectional structural view of a storage area of the frame transfer type CCD solid-state imaging device of FIG. 1;

FIG. 3 is a cross-sectional structure along line 2A-2A ′ and line 2B-2B ′ in FIG. 2 and a potential distribution diagram corresponding thereto.

FIG. 4 is a diagram showing a photoelectric conversion characteristic of the CCD solid-state imaging device of FIG. 1;

FIG. 5 is a configuration diagram of a frame transfer type CCD solid-state imaging device according to an embodiment of the present invention.

FIG. 6 is a sectional structural view of a frame transfer type CCD solid-state imaging device according to an embodiment of the present invention.

FIG. 7 is a cross-sectional structure taken along line 2A-2A ′ of FIG. 6A and a band diagram corresponding thereto.

8A and 2B-2 of FIG. 6A;
It is a cross-sectional structure in the B 'line, and the profile of the conduction band with respect to it.

9A and 2B-2 of FIG. 6A.
It is a cross-sectional structure in the B 'line, and the profile of the valence band with respect to it.

FIG. 10 is a cross-sectional structure taken along line CC ′ of FIG. 6A and a valence band profile corresponding thereto.

FIG. 11 is a waveform diagram of a four-phase driving clock signal employed in the CCD solid-state imaging device of the present invention.

FIG. 12 is a potential distribution diagram for each period of the CCD solid-state imaging device of the present invention.

FIG. 13 is a waveform diagram of a two-phase driving clock signal used in the CCD solid-state imaging device of the present invention.

FIG. 14 is a potential distribution diagram for each period of the CCD solid-state imaging device of the present invention.

[Explanation of symbols]

51: light receiving area, 52: accumulation area, 53: HCCD, 5
4,55 ... Charge detection and amplification circuit.

Claims (5)

(57) [Claims] 1. A light receiving area for generating signal charges with respect to incident light, a storage area for storing signal charges from the light receiving area for a certain period of time, and an HCCD for extracting the signal charges stored in the storage area line by line. A high-sensitivity signal charge detection and amplification circuit for detecting and amplifying signal charges for electrons among signal charges output from the HCCD; and detecting and amplifying signal charges for holes among signal charges output from the HCCD. A CCD solid-state imaging device comprising: a low-sensitivity signal charge detection and amplification circuit. 2. The light-receiving region includes a low-concentration substrate of a first conductivity type, a well of a second conductivity type formed on the substrate, and a first impurity region having a first conductivity type formed in the well. A second impurity region having a second conductivity type formed on a surface of the first impurity region; and a third impurity having a first conductivity type formed in the well in contact with the first and second impurity regions. The CCD solid-state imaging device according to claim 1, further comprising: a region; and a fourth impurity region having a high concentration of a second conductivity type and formed in the well in contact with the third impurity region. 3. The low-concentration substrate of a first conductivity type, a well of a second conductivity type formed on the substrate, and a first impurity region having a first conductivity type formed in the well. A second impurity region having a second conductivity type formed on a surface of the first impurity region; and a third impurity having a first conductivity type formed in the well in contact with the first and second impurity regions. The CCD solid-state imaging device according to claim 1, further comprising: a region; and a fourth impurity region having a high concentration of a second conductivity type and formed in the well in contact with the third impurity region. 4. The storage region further includes: an insulating film formed on the entire surface of the substrate; a transfer electrode formed on the insulating film; and a light-shielding film formed on the transfer electrode. 4. The CCD according to claim 3,
Solid-state imaging device. 5. A step of generating signal charges of electrons and holes with respect to incident light, a step of storing the generated signal charges for a predetermined time, and a step of extracting the stored signal charges line by line. Detecting signal charges for electrons among signal charges extracted line by line; detecting signal charges for holes among signal charges extracted line by line; detecting signal for electrons and detecting for holes When synthesizing signals, the detection signal for electrons is
Outputs the value to which the detection signal for the hole is added,
Outputting a detection signal for a hole in a region, and a signal processing method for a CCD solid-state imaging device.