JPH0746722B2 - Driving method for charge transfer type imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a charge transfer device (charge coupled device) for extracting a photoelectric conversion device and optical information of each device on a semiconductor substrate.
Device: Charge Coupled Device (hereinafter CCD)
The present invention relates to a solid-state imaging device using the.

[Background of the Invention]

The solid-state imaging device needs to have a resolution similar to that of an imaging electron tube used in the current television broadcasting,
For this reason, a pixel matrix in which 500 pixels in the vertical direction and 800 to 1000 pixels in the horizontal direction are arranged and a corresponding scanning element are required. Therefore, the solid-state imaging device is manufactured by using the MOS large-scale circuit technology that requires high integration, and CCD or MOS transistors are generally used as the constituent elements. Figure 1 (a) shows a frame interline transfer ( F rame Input ) featuring low smear and low noise.
ine T ransfer: FIT) shows a CCD imaging device of the system (Horii et al., "miniaturization of CCD solid-state imaging device," 1983 television Society National Conference Proceedings pp.55-56). This element consists of a photodiode 1 and a vertical CCD shift register 2, and an imaging area 3
And a horizontal CCD shift register 5 that transfers the signal charges sent from the storage region 4 row by row toward the output. In this device, the signal charge is vertical CC
The high-speed driving of D2 causes the charges to be sent to the imaging region 4 within a short period of time, and unnecessary charges (dark current etc.) other than that are sent to the drain region 7 by selecting the gate 6. Therefore, it was possible to suppress the smear, which was an important problem in the conventional interline CCD image storage device, and to significantly improve the image quality (smear is an excessive amount of light generated when intense incident light is generated. The charge also leaks to the vertical CCD area, causing white vertical stripes on the monitor). Here, 8 is a charge read gate, 9a to 9d are transfer directions of optical signal charges, and 9e is a transfer direction of unnecessary charges.

However, another problem of the CCD imager, the afterimage, remains unsolved. This afterimage is generated by the following operation mechanism. FIG. 1 (b) is a view showing a cross-sectional structure of a pixel constituting the image pickup area shown in FIG. 1 (a), 1 is a photodiode, 2a is a CCD electrode also serving as a transfer gate 8, and 2b is a buried channel. A layer (channel means a region through which a charge passes) is shown. Further, 10 is a substrate, 11 is an insulating oxide film for pixel separation, and 12 is an oxide film that insulates the electrode from the substrate. The signal read operation will be described with reference to FIG. When reading the optical signal charge Q _S accumulated in the photodiode 1 to the vertical CCD shift register 2, a high voltage (“H” level) is applied to the transfer gate 8 to which the intermediate voltage (“M” level) has been applied so far. Is applied (this voltage is also applied to the CCD electrode 2a). As a result, the potential under the transfer gate 8 drops from φ _OFF to φ _ON , and the photodiode 1
The electric charge stored in the vertical CCD shift register 2 flows into the vertical CCD shift register 2 as shown by arrow 13. By the way, as the reading of charges to the CCD2 side progresses, the potential φ _PD on the photodiode 1 side decreases. Therefore, the conductance of the transfer gate 8 decreases, and as a result, the charge Q that cannot be read out in a predetermined period is reached.
_R remains in the photodiode, which will be read in the subsequent fields. This unread charge causes an afterimage. This kind of afterimage occurs more as the amount of incident light decreases. Was but connexion, the (amount of incident light afterimage has led to deterioration in image quality per markedly eye in imaging low light conditions is small, the amount of charge accumulated in the photodiode, that is, the voltage change amount [Delta] [phi _PD less, the read start Sometimes the transfer gate conductance is kept low).

[Object of the Invention]

An object of the present invention is to solve the above problems, that is, to provide a driving method of a CCD type image pickup device which prevents an afterimage when reading a signal.

[Outline of Invention]

To achieve the above object, the present invention provides a vertical CCD shift register with a bias charge input section for injecting charges. The operation of this device is as follows. Send to CCD,
This bias charge is sent to the photodiode side via the transfer gate, and (iii) finally, the optical signal charge left in the photodiode is returned to the vertical CCD side together with the bias charge, and this charge (read-out light Signal charge + bias charge)
The residual image charge is swept out of the element by a charge transfer procedure of discharging the residual charge to the outside.

Example of Invention

 Hereinafter, the present invention will be described in detail with reference to examples.

2A to 2C show the configuration and drive bias of the CCD image pickup device of the present invention. In FIG. 7A, reference numeral 14 is a bias charge input section. FIG. 2B shows the structure of the pixels forming the imaging area, and 8'denotes a transfer gate. This transfer gate 8'cannot be used as the CCD electrode 2a as in the conventional device shown in FIG. 1 in order to realize the driving method of the present invention, and therefore the CCD electrode 2'a and the gate electrode 8 '. a is formed of another electrode (the electrode 2'a is formed of, for example, the first-layer polycrystalline silicon, and the electrode 8'a is formed of, for example, the second-layer polycrystalline silicon). FIG. 2 (c) is a driving pulse used for driving the device of the present invention, and V _I (n) is a vertical CC of the imaging region.
This is a clock pulse that drives the D shift register 2.
This clock pulse V _I (n) is two or more (for example, 2
Phase, 3 phase, 4 phase, etc.), among which 1
The type is shown. V _R is a read pulse applied to the gate electrode 8'a. V _S (n) is a clock pulse that drives the CCD shift register in the storage area. There are as many pulses as necessary to drive the CCD shift register in the storage region, but one of them is representative.

The afterimage generation preventing operation by the driving method of the present invention will be described with reference to FIG.

When the potential of the transfer gate in addition to the transfer gate a read pulse V _R "1" level at time A t ₁ decreases to phi _ON, the light signal charge accumulated in the photodiode is read to the vertical CCD side. The potential phi _PD with the signal readout decreases, residual image charge Q _R is left in the photodiode side since the conductance of the transfer gate is reduced. This read operation is the same as that of the conventional device shown in FIG. 1 (corresponding drawings 2 (c), 3 (a), b)).

B At time t ₂ , the charge (Q _S −Q _R ) of the vertical CCD ₂ is transferred to the CCD in the storage region via 6 by the high frequency clock pulses V _I (n) and V _S (n), and is stored in the storage region until time t _6. It is temporarily stored (corresponding drawings 2 (c) and 3 (a)).

The bias charge Q _B is sent from the input unit 14 to each stage of the vertical CCD by the vertical CCD operated by the high frequency clock pulse V _I (n) from the C time t ₃ (FIGS. 2 (c) and 3 (c)). .

The D time t ₄ at "1" level of the read pulse V _R is applied to the transfer gate 8 ', phi again from phi _OFF the potential of the transfer gate
_Falls to _ON . As a result, "0" Q _B from CCD electrode side level of the clock pulses V _{I (n)} is applied is fed to the photodiode side, together aforementioned residual image charge Q _R and bias charge Q _B is the photodiode (FIG. 2 (c), FIG. 3 (c), (d)).

E Then, the clock pulse becomes "1" level.
The charge (Q _R + Q _B ) is read from the photodiode side to the CCD side (FIGS. 3 (c) and (e)). In this reading, residual image charge Q because _R is fed to the CCD side with bias charge, almost completely charge in a short period of time (Q _R +
Q _B ) can be sent to the CCD side. Of course, even at the time of this reading, microscopically, the charge Q _r is left unread on the photodiode side, but due to the presence of the bias charge, the charge Q _r
r is negligibly small compared to Q _R. This charge Q _r can be made smaller as Q _B is made larger.

At F time t ₅ , the charge (Q _R + Q _B ) is transferred through the vertical CCD operated by the high frequency clock pulse V _I (n) and is swept to the drain 7 via 6.

After the G, H vertical blanking period (T _BL ), and the video period starts at t ₆ , the optical signal charge (Q _S −Q _R ) temporarily stored in the storage region by the clock pulse V _S (n) is sequentially horizontal. It is sent to the CCD5 and further sent to the output via the horizontal CCD (Fig. 2 (c), Fig. 3 (a)).

Above mentioned A~H charge Q _R left on photodiode during optical signal read by the operation of transported placed on a large bias charge Q _B of the charge quantity after completion optical signal read, Q _R, Q _B are both outside of the device Swept to. As a result, the afterimage is 1/10 to 1/10 of that in the conventional driving by the driving method of the present invention.
It becomes possible to reduce to 0.

In the above-described embodiment, the bias charge is input from the input section 14 and swept out to the drain 7, but the following driving method can be considered.

FIG. 4 shows an embodiment in which the bias charge is input from the input part and is swept back to the input part together with the residual image charge.

Reading of A to B optical signal charges and transfer to the storage region are the third
The operation is similar to that shown in FIG.

Bias charge Q _B is input from _C to E 14, and further Q _B
The feed to the photodiode side, followed by the residual image charge Q _R again returned to the vertical CCD side with Q _B, these operations are also similar to that shown in FIG. 3 (c).

The F charge (Q _R + Q _B ) is swept back to the input section 14 by performing a reverse transfer operation on the vertical CCD. Vertical here
Reverse transfer of the CCD can be performed by reversing the phase relationship of the clock pulse V _I (n) just as when the optical signal Q _S was sent to the storage section.

The optical signal charges temporarily stored in the G and H storage areas are sequentially input to the horizontal CCD and read out to the output via the horizontal CCD.

FIG. 5 shows a driving method in which the input section 14 is not provided, but the bias charge is inputted from the drain 7 provided for taking out the unnecessary charge and the afterimage charge and the bias charge are swept out to the drain again. . Readout of optical signal charge (A ~
B, G to H) are the same as in the case of FIG. Here, the reverse transfer operation described above is performed when the bias charge input from the drain is carried, and the charge (Q _R + Q _B ) is transferred in the vertical CCD by the same forward transfer operation as the optical signal charge, and is swept to the drain 7. Will be issued.

In the driving method shown in FIGS. 3 and 4, the bias charge input and the afterimage charge (including the bias charge) are all discharged within the vertical period, but these operations are not performed during the video period. You may start from. In the video period,
The optical signal charge is read from the storage area to the output via the horizontal CCD. On the other hand, the clock pulse V shown in FIG.
Driving the vertical CCD2 by slightly deforming _I (n),
It is possible to sweep out afterimage charges at the same time when the optical signal is being taken out.

〔The invention's effect〕

As described above in detail with reference to the embodiments, by using the driving method of the present invention, it is possible to prevent the afterimage which has been a problem of the CCD image pickup device. Moreover, since the present invention can be realized without complicating the element structure,
The practical effect of the present invention is very large.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration, structure, and operation of a conventional CCD image sensor, and FIG. 2 is the configuration of the CCD image sensor of the present invention.
FIG. 3 is a diagram showing a structure and a driving pulse, FIG. 3 is a diagram showing an element operation by a driving method of the present invention, and FIGS. 4 and 5 are element configurations and driving operations different from those of the embodiment of FIG. 2 of the present invention. FIG.

Claims (3)

[Claims] 1. A photoelectric conversion element provided two-dimensionally on the same semiconductor substrate, a vertical CCD for vertically transferring optical signal charges detected by the photoelectric conversion element, and the above-mentioned vertical CCD for transfer. In a driving method of a charge transfer type image pickup device having a storage unit for temporarily storing optical signal charges and a horizontal CCD for transferring the optical signal charges of the storage unit toward an output, the light read from the photoelectric conversion element is used. A process of transferring signal charges to the storage unit via the vertical CCD, a process of sending bias charges to the photoelectric conversion device via the vertical CCD after the optical signal charge transfer process, and the light from the photoelectric conversion device. When the signal charge is read out, there is a step of flowing out the unread optical signal charge unread in the photoelectric conversion element to the outside through the vertical CCD together with the bias charge sent to the photoelectric conversion element. The driving method of the charge transfer type imaging device according to symptoms. 2. The bias charge is sent to the photoelectric conversion element from one end of the vertical CCD, and the unread optical signal charge and the bias charge are discharged to the outside from the other end of the vertical CCD. A method of driving a charge transfer type image pickup device according to claim 1, wherein 3. The bias charge is sent to the photoelectric conversion element from one end of the vertical CCD, and the unread optical signal charge and the bias charge also flow out to the outside of the one end of the vertical CCD. A method of driving a charge transfer type image pickup device according to claim 1, wherein