JPH0834565B2 - Charge transfer type solid-state image sensor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a charge transfer type solid-state imaging device, and more specifically, to a photoelectric transfer device on a semiconductor substrate and a charge transfer device (Charge Transfer Device) for extracting optical information of each device. ) Is mounted on the solid-state imaging device.

[Background of the Invention]

The solid-state image pickup device is required to have a resolution equal to or higher than that of an image pickup electron tube conventionally used in television broadcasting. Therefore, a pixel (photoelectric conversion element) matrix in which 500 in the vertical direction and 800 to 1000 in the horizontal direction are arranged on the semiconductor substrate and a scanning element corresponding thereto are required. Therefore, the solid-state image pickup device is manufactured by using the MOS large-scale circuit technology capable of high integration.
An imaging device using a Charge Coupled Device (hereinafter abbreviated as CCD) has been developed as a charge transfer device for taking out signal charges accumulated in a photoelectric conversion device. This type of device is described in, for example, the 1980 National Convention Proceedings, P33-P34, which commemorates the 30th anniversary of the Television Society.

FIG. 9 is a basic configuration diagram of a conventional CCD type solid-state imaging device.

In FIG. 9, 1 is a photoelectric conversion element formed of, for example, a photodiode, 2 and 3 are vertical CCD shift registers and horizontal CCD shift registers for taking out the optical signals accumulated in the photoelectric conversion element group to an output end 4, 5- 1,5-2,6-1,6
Reference numeral -2 is a generator for generating a clock pulse for driving the vertical CCD shift register 2 and the horizontal CCD shift register 3, respectively. Although a two-phase clock pulse generator is shown here, any of four-phase to three-phase clock forms may be adopted. Reference numerals 7-1 and 7-2 denote transfer gates for sending the charges accumulated in the photodiode to the vertical shift register 2. The solid-state image sensor of FIG. 9 is a black-and-white image sensor as it is, and when a color filter is stacked on the solid-state image sensor, each photodiode is provided with color information and becomes a color image sensor.

As is well known, the solid-state image pickup device has advantages such as small size, light weight, maintenance-free, low power consumption, etc., and is expected as a next-generation image pickup device in place of the electron tube image pickup device.

However, the conventional CCD type solid-state image pickup device has the following two problems, which significantly impairs the image quality.

(I) Since interlaced scanning is performed in the vertical direction,
Pixel signals of odd columns (1,3,5, ... 2N-1) are read in the first field, and pixel signals of even columns (2,4,6, ... 2N) are read in the second field. As a result, in the first field of the next frame, the signal of the column that has not been read in the previous field (that is, the odd column) is read in addition to the new signal (this phenomenon is generally called afterimage). . The solid-state image sensor has an advantage that it does not generate an afterimage because the switching speed is high, but actually, an afterimage is generated based on the interlace reading method as described above.

As a method for solving this problem, two vertical CCDs are provided (that is, two times the vertical CCDs shown in FIG. 9 are provided), and the odd and even pixel combinations of all columns are combined in any field. It is conceivable to read out the signal.
However, since the number of vertical CCDs is doubled, the area allowed for the photodiode is significantly reduced (that is, the aperture ratio is reduced from 35-40% to 15-20%), which is important for the image sensor. A problem arises that the light sensitivity, which is an item, becomes low.

(Ii) On a monitor with a large amount of incident light, white vertical stripes appear at the top and bottom of a subject image with a large amount of incident light (this phenomenon is generally called smear), and the image quality is greatly impaired as with the afterimage described above.

Therefore, solving the above-mentioned problems (i) and (ii) is a major problem in the conventional solid-state imaging device.

[Object of the Invention]

An object of the present invention is to eliminate these two problems, that is, afterimages and smears, and to provide a charge transfer type solid-state image pickup device having good image quality.

[Outline of Invention]

In order to achieve the above object, a charge transfer type solid-state imaging device according to the present invention has photoelectric conversion element groups arranged in a matrix on the same semiconductor substrate and photoelectric signal charges accumulated in the photoelectric conversion element group. Charge of a method in which a vertical charge transfer element for transferring in the horizontal direction and a horizontal charge transfer element for transferring the output charge from the vertical charge transfer element in the horizontal direction are integrated and the pixel signal from the photoelectric conversion element group is read out to the outside. In the transfer-type solid-state imaging device, the vertical charge transfer device includes two electrodes for taking in a first pixel signal charge and a second pixel signal charge from the photoelectric conversion device group, and one electrode for holding a smear charge. There are a plurality of groups each consisting of one electrode that does not retain electric charge, and the first pixel signal charge is applied to the vacant electrode, and the smear charge is applied to the vacant electrode where the first pixel signal charge advances first. , Followed by smear charge The first to electrodes empty proceed to 2
Is controlled so as to sequentially repeat the operation of moving the pixel signal charges of the above, and after the output of the horizontal charge transfer element, the transferred first pixel signal charges and the second signal charges A subtractor for subtracting the transferred smear charge is provided.

Example of Invention

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

FIG. 1 is a basic configuration diagram of a charge transfer type solid-state imaging device showing an embodiment of the present invention.

In FIG. 1, 1-1 and 1-2 are photo diodes, 2 '
Is a vertical CCD provided with the ion implantation region 8 for performing a triple transfer operation, 2'-1,2'-2 ... Is an electrode constituting the vertical CCD 2 ', 3'-1,3'-2,3' -3 is a horizontal CCD that receives the two types of signal charges Q _A , Q _B , and q _S sent by the vertical CCD 2'and transfers each charge toward the outputs 4-1, 4-2, 4-3, 5'-
1,5'-2,5'-3,5'-4 are vertical clock pulse generators for driving the vertical CCD 2 '. Here, the horizontal clock pulse for driving the horizontal CCD 3'is omitted in order to simplify the drawing, but it may be two phases as shown in FIG. 9, or three phases or four phases. Below the three electrodes of the four electrodes 2'-1, 2'-2, 2'-3, 2'-4 that constitute the vertical CCD 2 ', two series of optical signals Q _A , Q _B Smear q _S
Are accumulated and the remaining one electrode is left empty. Then, by the triple transfer mode described later, the optical signals Q _A , q _S ,
Q _B is fed to the horizontal CCD3'-1,3'-2,3'-3.

2 (a) and 2 (b) are a plan view and a cross-sectional structural view of a pixel portion constituting the CCD type solid-state imaging device of FIG.

2'-1 (or 2'-3) and 2'-2 (or 2'-4) are electrodes forming a vertical CCD 2 ', for example, 2'-1 is polycrystalline silicon of the first layer, 2'-2 is formed of the second layer of polycrystalline silicon. Each electrode 2'-2
Underlying 2'-4 is an ion implantation layer 8 formed prior to fabrication of these electrodes, which layer 8 is composed of, for example, boron atoms. Here, the transfer gate 7-1
(Or 7-2) shows the case where it is also used as the CCD electrode 2'-1, but it may be formed of polycrystalline silicon of the third layer, for example, separately from the CCD electrode 2'-1.

When the plane of FIG. 2 (a) is cut along the xx ′ plane, the second
The sectional structure shown in FIG.

In FIG. 2 (b), 9 is the CCD electrode 2'and the substrate 11
Gate oxide film that insulates (for example, P type), and 10 is CCD
Layer for making the electrode transfer channel of
Type). If the surface of the channel is used, this layer 10 is not necessary.

FIG. 3 is an explanatory diagram showing the triple transfer operation of the vertical CCD.

As shown in FIG. 3A, each line of the clock pulse generators 5'-1 to 5'-4 has electrodes 2'-1,
2'-2, 2'-3, 2'-4, 2'-1 ... Are sequentially connected. Electrodes 2'- _1, 2'-2, 2'- at times t _{1 to} t _n
The potential under 3,2'-4, ... Is shown in FIG. 3 (b), and the positions of the electrodes correspond to those in FIG. 3 (a).

 The triple transfer operation will be described with reference to FIG.

(I) At t = t ₁ , the signal charge Q accumulated in the photodiodes 1-1 and 1-2 is caused by the light incident in one field period.
_A and Q _B are high-voltage (“H” level) clock pulses V ₁ and V
₃ is added and is fed to the vertical CCD 2'side through the transfer gates 7-1 and 7-2 in the conductive state (potential lowered), and the lowest electrodes 2'-1 and 2'- of the potential.
Accumulated under 3.

(Ii) At t = t ₂ , the clock pulse applied to each electrode is at a low voltage (“L” level) and the potential under each electrode is high, but the ion implantation formed at a part under each electrode Due to the barrier V _B formed by the layer 8, the charges Q _A and Q _B have a time t =
It is stored under the same electrode as at t ₁ .

(Iii) At t = t ₃ , the vertical scanning period starts, so
Q _A and Q _B are transferred to the horizontal CCD. Note that t = t ₁ , t
₂ is the time within the vertical blanking period.

First, by the intermediate voltage (“H” level) applied to the electrode 2′-4, the charge Q _B accumulated in the electrode 2′-3 is transferred to the lower side of the electrode 2′-4.

(Iv) At t = t ₄ , the smear charge q _S accumulated so far in the electrode 2′-2 is transferred to the lower side of the electrode 2′-3 to which the “M” level clock pulse V ₃ is applied. . Here, the smear charge is generated by the charge generated by the light incident leaking to the vertical CCD side, and also leaks during the subsequent transfer period (t _{4 to} t _m ). The amount of smear charge increases with the passage of time. On the other hand, since the leaked electric charge enters any of the electrodes, smear electric charge is mixed into the signals Q _A and Q _B, and the smear component in the signal also increases with the passage of time.

(V) At t = t ₅ , the “M” level clock pulse V ₂ is applied to the electrode 2′-2, and the charge Q _A accumulated in the electrode 2′-1 is transferred to the lower part of the electrode 2′-2. It

By the above operation time t ₃ ~t _5, a charge Q _B, q _S, Q _A is one minute electrodes only, will have been transferred to the horizontal CCD side.

In this way, charge is made to exist in three of the four electrodes, one electrode is placed in an empty state, and signal A is passed to the empty electrode and then signal A advances and becomes empty. Signal B to the electrode
Next, the transfer operation is a transfer operation of moving the signal C to an electrode which has become emptied due to the advance of the signal B. Such a transfer operation will be hereinafter referred to as a triple transfer operation.

(Vi) t = At t _6, starts again the charge Q _B transfer, the intermediate voltage ( "M" level) by the charge accumulated in the electrode 2'-4 Q _B is electrode 2 applied to the electrodes 2'-1 '-1. By repeating the triple transfer operation in this manner, the three signals Q _B , q _S , and Q _A are transferred to the horizontal CCD side, and when reaching the final electrode of the vertical CCD,
Q _B, q _S, Q _A is fed to the horizontal CCD3'-1,3'-2,3'-3 each. The charges are sent to the horizontal CCD within the horizontal blanking period, and when the horizontal scanning period starts, the signals Q _B , q _S , and Q _{A are} input.
Are simultaneously transferred in the horizontal CCD toward outputs 4-1, 4-2 and 4-3. Since one horizontal CCD 3'-1, 3'-2, 3'-3 is provided for each signal, the charge of the horizontal CCD is the same as that of the conventional horizontal CCD (3. The transfer may be performed by expressing the normal operation for the double transfer operation).

The state of time t = t _n in FIG. 3B shows that the smear charge amount increases as the transfer progresses with the passage of time (the thick black line indicates the smear charge amount). In this case, within adjacent groups (eg [Q _{B (n)} , q _{S (n)} ,
The smear charges in the group of Q _{A (n)} ] and the group of [Q _{B (n + 1)} , q _{S (n + 1)} , Q _{A (n + 1)} ] are almost the same. That is, the amount of smear charge leaked to the signals Q _{A (n)} and Q _{B (n)} is q
_It is equal to _{S (n)} .

 Next, the subtraction of smear charges will be described.

FIG. 4 is a diagram showing the basic configuration of the smear removing circuit.

12-1, 12-2, 12-3 are horizontal CCDs 3'-1, 3'-2, 3'-3
The charge detection circuit provided at the final stage of the
An S source follower circuit is used. 4-1, 4-2 and 4-3 are outputs of the charge detection circuit, and 13-1 and 13-2 are subtractors. The subtracters 13-1 and 13-2 may be provided outside the device using a commercially available differential amplifier, or may be a form in which a MOS differential amplifier is integrated inside the device.

FIG. 5 is a diagram showing output waveforms of the optical signal charges Q _A , q _S , and Q _B in FIG.

FIG. 5 shows the waveforms of the outputs 4-1, 4-2 and 4-3 detected by the charge detection circuits 12-1, 12-2 and 12-3, and the subtractor 13-.
The waveforms of the outputs 14-1, 14-2 of 1, 13-2 are shown. As described above, since signals of the same group represented by m, n, etc. contain the same amount of smear signal components (the black portion of the waveform in FIG. 5 is the smear signal), the output 4- 1 and 4-2
The by inputting the subtractor 13-1, the true optical signal O _A no smear component in the output 14-1 and the output 4-3 and 4
-2 is input to the subtractor 13-2 to output 14-2
Again true light signal O _B without smear component is obtained each of the.

FIG. 6 is a block diagram of a CCD type image pickup device showing another embodiment of the present invention.

In the embodiment shown in FIG. 1, three signal charges Q _A , q _S , and Q _B are set to 3
The data is transferred by the horizontal CCD of the column, but in FIG.
The signal charges Q _A , q _S , and Q _B are transferred by the horizontal CCD in two columns.
In this case, two signals (for example, Q
_It suffices to send _A , Q _B ) and send one signal (for example, q _S ) by the other horizontal CCD.

Therefore, the horizontal CCD 3 ″ -2 that transfers two signals is made to perform the double transfer operation, and the horizontal CC that transfers one signal.
D3'-1 is made to perform a single transfer operation. The double transfer operation is 3 connected to the line from the clock pulse generator.
Electrodes that have electric charges present in two of the electrodes and one electrode is in an empty state, and transfer the signal A to this empty electrode, and then the signal A advances and becomes empty This is a transfer operation of transferring the signal B to.

FIG. 7 and FIG. 8 are configuration diagrams of a CCD image pickup device showing still another embodiment of the present invention.

In FIG. 7, the three signals Q _A , q _S , and Q _B are transferred by one row of horizontal CCDs. In this case, horizontal C
Like the vertical CCD, the CD also needs to perform triple transfer operation.

When arranging a plurality of rows of horizontal CCDs as in the case of the embodiment of FIGS. 1 and 6, it is not necessary to make the channel width of each horizontal CCD the same. For example, since the smear charge amount is generally smaller than the light signal charge amount by one digit or more, as shown in FIG. 8, the channel width W ₂ of the horizontal CCD 3'-2 for smear charge transfer is set to another optical signal transfer. Horizontal CCD channel width W ₁ , W
_It may be smaller than ₃ . Here, the following three types of cases can be considered as the magnitude relationship of the channel width of each horizontal CCD.

W ₂ <W ₁ = W ₃ (makes the channel widths of Q _A and Q _B equal) W ₂ <W ₁ <W ₃ (makes the channel width of Q _A smaller than Q _B ) W ₂ <W ₃ <W ₁ (Q greater than Q _B the channel width _a) in the embodiment of FIG. 1, horizontal for smear charge transfer
CCD3'-2 is a horizontal CCD3'- which transfers signal charges Q _A and Q _B
While disposed between the 1 and 3'-3, the signal charge transfer sequence of the aforementioned vertical _{CCD2 '(Q B, q S} , Q A) in addition to, Yotsute to varying the way of driving , (Q _S , Q _B , Q _A ), or (Q _A , Q _B , q _S ), and so on.

Therefore, for example, the horizontal CCD 3'-1 may be used for smear charge transfer, and the horizontal CCDs 3'-2, 3'-3 may be used for signal charge transfer.

In the present invention, by operating the vertical CCD in the triple transfer mode, the same aperture ratio (35 to 40
%), Three types of signals (two optical signals and one smear signal) can be transferred. Then, by subtracting each of these two types of optical signals and the smear signal, it is possible to obtain two types of true optical signals (that is, odd-numbered columns and even-numbered columns) without smear signals.

As a result of evaluation by an experiment conducted by the present inventors, about 50% of the interlace afterimage, which had been a problem in the conventional device, completely disappeared (becomes 0%), and smear was reduced by about 10% compared with the conventional device. It became clear that it could be reduced by 40 dB.

In addition, in the embodiment, the description has been made by taking a typical interline CCD element as a conventional solid-state image sensor, but the present invention is not limited to this method, and another method, for example, a frame transfer CCD. The same can be applied to shaped elements and the like.

〔The invention's effect〕

As described above, according to the present invention, two optical signals and one smear signal are transferred while maintaining the same aperture ratio as the conventional element, and each optical signal and the smear signal are subtracted. The smear can be significantly reduced compared to the conventional one, and the image quality of the CCD type solid-state image pickup device can be improved by completely removing the afterimage due to interlacing.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a charge transfer type solid-state image pickup device showing an embodiment of the present invention, FIG. 2 is a plan view and a sectional structure diagram of a pixel portion of the CCD type solid-state image pickup device of FIG. 1, and FIG. FIG. 4 is a diagram showing a triple transfer operation of a vertical CCD, FIG. 4 is a basic configuration diagram of a smear removing circuit of the present invention, FIG. 5 is a diagram showing output waveforms of optical signal charges in FIG. 1, FIG. 6, and FIG. FIG. 8 and FIG. 8 are configuration diagrams of a CCD type solid-state image pickup device showing another embodiment of the present invention, and FIG. 9 is a basic configuration diagram of a conventional CCD type solid-state image pickup device. 1-1, 1-2: Photo diode, 2 ': Vertical CCD, 2'-1,
2'-2,2'-3,2'-4: electrode, 3'-1,3'-2,3'-3,
3 ″ -2,3: Horizontal CCD, 4,4-1-1,4-2,4-3: Output terminal, 7
-1,7-2: Transfer gate, 5-1, 5-2,6-1,6-2: Clock pulse generator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinya Oba 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Haruhisa Ando 1-280 Higashi Koigakubo, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (72) Inventor Toshifumi Ozaki 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Central Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-56-12179 (JP, A)

Claims (3)

[Claims] 1. A photoelectric conversion element group arranged in a matrix on the same semiconductor substrate, a vertical charge transfer element for vertically transferring optical signal charges accumulated in the photoelectric conversion element group, and the vertical charge. In the charge transfer type solid-state imaging device of the type in which a horizontal charge transfer device that transfers the output charge from the transfer device in the horizontal direction is integrated, and the pixel signal from the photoelectric conversion device group is externally read out, the vertical charge transfer device is , A plurality of pairs of two electrodes for taking in the first pixel signal charge and the second pixel signal charge from the photoelectric conversion element group, one electrode for holding smear charge, and one electrode for not holding charge A pair of empty electrodes with a first pixel signal charge, followed by a first pixel signal charge with a smear charge to the emptied electrode, followed by a smear charge with a vacancy. Second to the electrode
Is controlled so as to sequentially repeat the operation of moving the pixel signal charges of the above, and after the output of the horizontal charge transfer element, the transferred first pixel signal charges and the second signal charges A charge transfer type solid-state image pickup device comprising a subtracter for subtracting the transferred smear charges. 2. The horizontal charge transfer element transfers a first pixel signal charge, a second pixel signal charge and a smear charge by three columns of horizontal charge transfer elements or two columns of horizontal charge transfer elements. The charge transfer type solid-state image pickup device according to claim 1, wherein the charge transfer is performed by one row of horizontal charge transfer elements. 3. When the horizontal charge transfer elements are provided in two rows or three rows, the channel widths of the charge transfer elements are set to have a magnitude relation to change the charge transfer ability. 2. A charge transfer type solid-state image sensor according to item 2.