JPS5869178A - Driving method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To improve the blooming phenomenon and the picture quality, through the suppression of spread of spot optical image, by operating readout of signal charges of a photoelectric conversion element train after sweeping out a part of electric charges of saturated charges of the photoelectric conversion element train. CONSTITUTION:On a semiconductor substrate 20, a photoelectric conversion element 13 consisting of a junction photo diode, transfer electrodes 14, 16 and a photoelectric conversion element train consisting of a buried layer 15 are arranged. Before saturated charges 25 of the photoelectric conversion element overflow from a potential 23 under the transfer electrode 16 through the incidence of a light, a saturated exposure amount or over to the element 13, a part of the transfer electrode 16 is opened, allowing to sweep out charges 27 to be thrown away from the element 13. After a margin is provided for the element 13 to the charge 17 and a signal charge 28, the transfer electrode 16 is closed to read out the signal charge 28, allowing to suppress the spread of the spot optical image and improve the picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a solid-state imaging device,
Charge overflow phenomenon (blooming phenomenon) in solid-state imaging devices
The purpose is to suppress the

FIG. 1 shows an example of a configuration of a charge transfer type solid-state imaging device to prevent the blooming phenomenon without using a so-called overflow drain that absorbs overflowing charges. 1 is a photoelectric conversion element array, 2 is a charge transfer element array that vertically transfers photoelectrically converted signal charges, 3 is an accumulation region that temporarily accumulates the signal charges sent from the charge transfer element array 2, and 4 is an accumulation area. This is a readout area where signal charges from the area are read out line by line.

The photoelectric conversion element array 1 and the charge transfer element 2 constitute an imaging region. The accumulation region 3 is a region for temporarily accumulating signal charges sent from the imaging region, and is therefore shielded from light.

A conventional driving method for preventing the blooming phenomenon in the solid-state imaging device having the above configuration will be described below. Light incident on the photoelectric conversion element array 1 is photoelectrically converted, generates charges, and is accumulated. Charges generated in excess of the saturation charge amount overflow to the charge transfer element 2. After a certain photoelectric conversion period, the charges stored in the photoelectric conversion element array 1 are sent to the charge transfer element array 2, but many overflowing charges due to blooming remain in the charge transfer element array 2. In order to sweep out this residual charge, a pulse voltage is applied to the charge transfer element array 2, and the residual charge is swept out through a predetermined drain region, storage region, or readout region in a short period of time. After this operation, the signal charges of the photoelectric conversion element array are sent to the charge transfer element array 2-1. The signal charges sent to the charge transfer element array are sent to the storage region 3 in a short period of time. The signal charge transferred to the storage area is 1
The data is transferred line by line to the readout area 3 and sequentially read out. When the charge force meter in the storage region is read out from the readout region, charges are generated and accumulated by incident light in the photoelectric conversion element array 1, and blooming charges are accumulated in the charge transfer element array 2.

FIG. 2 shows an example of applied pulses for performing the above operation, and shows pulse voltages φv1, . φV21φs1゜φS2 is the pulse voltage φPT applied to the electrode that transfers the signal charge of the photoelectric conversion element array 1 to the adjacent charge transfer element array 2, and the signal charge in the charge transfer element array 2 of the imaging region is transferred to the charge transfer element of the storage region. Pulse voltage φVT applied to transfer electrode 6 to transfer to column
This is an example of the following.

The pulse voltage at time t1 is a pulse voltage that sweeps out the blooming charges in the charge transfer element array 2 in the imaging region through the accumulation region, and at the subsequent time t2, the signal charges in the photoelectric conversion element array 1 are transferred to the adjacent charge transfer element array 2. The electrode is opened (
φPT), a Norse voltage is applied at the next time t3 to transfer the charge transfer element array 2 in the imaging region to the charge transfer element array in the storage region. Times 11 and 12 degrees t3 are selected to fall within the vertical retrace period during which no captured image appears. The signal charges sent to the storage region after this time are sequentially sent to the readout region 4 line by line.

In such conventional driving methods for solid-state imaging devices, blooming exhibits blooming control ability for incident light that exceeds the saturation exposure amount. This has the disadvantage that a thin white vertical line appears on the image because the signal charge does not pass through it. Figure 3 is an illustration of the blooming phenomenon that occurs in the conventional driving method. 6 is a spot light image that exceeds the saturation exposure amount.
7 is a thin vertical line image that appears in the spot light image by performing the sweeping drive.

FIG. 4 is a schematic diagram for explaining the drawbacks of the conventional driving method. That is, this figure is a diagram showing a schematic diagram of the portion where the spot light is incident, which explains the cause of the white vertical lines appearing above and below the strong spot light image described above. 8
is the photoelectric conversion element portion into which intense spot light is incident. The charges overflowing from the photoelectric conversion element section spread into the adjacent charge transfer element array 9. After a certain photoelectric conversion period, the signal from the photoelectric conversion element 8 is sent to the storage region through the charge transfer element array 9, but before this operation, an operation is performed to sweep out the charges overflowing into the charge transfer element array. (Time t1 in Figure 2).

Blooming is controlled by this action.

However, even during the time when this sweeping drive is performed, charge overflows from the photoelectric conversion element section 8 into which a spot light stronger than the saturation exposure amount is incident. When the charge transfer element array 9 is operated to perform sweeping, the overflowing and accumulated charges are swept out, and at the same time, the charges overflowing from the photoelectric conversion element section 8 during this sweeping operation time are also transferred in the transfer direction. Become. Therefore, due to the sweeping drive, some overflowing charges exist in the charge transfer element array 9 adjacent to the photoelectric conversion element portion where strong spot light enters. The amount of charge existing in the charge transfer element array 9 that overflows during the sweep operation is strongly dependent on the sweep frequency. That is, if the light is swept out at a fast frequency, the overflowing photoelectric conversion element section 8 can be passed through in a short time, so that the influence of the overflow can be reduced. However, even if the frequency is increased, if the incident light of the spot light is strong and a large amount of overflow occurs, its influence cannot be ignored.

After the sweep drive, the signal charges in the photoelectric conversion element array section 8 are transferred to the charge transfer element array 9 and then to the storage region, but at this time, overflowing charges exist in the portion 12 of the charge transfer element array during the sweep drive. Therefore, it mixes with the signal charge and appears as a white vertical line as shown in Figure 3. For this reason, although the spread of the spot light image is suppressed, thin white vertical lines appear, degrading the image quality.

A driving method for a solid-state imaging device according to the present invention aims to improve the blooming phenomenon that occurs in the conventional driving method described above and improve image quality.

As mentioned above, charge overflows from the photoelectric conversion element part on which spot light exceeding the saturation exposure amount is incident even during sweep drive.
It is necessary to prevent charges from overflowing and being output from the photoelectric conversion element on which the strong spot light is incident. In the present invention, before performing sweep drive, the electrodes that transfer signals from the photoelectric conversion element array to the charge transfer element array are partially opened, and part of the charge of the saturated signal in the photoelectric conversion element array is sent to the charge transfer element array. Sweeping is performed during sweeping drive.

Figures 6) to 6(d) are schematic diagrams for explaining a method of driving a solid-state imaging device in an embodiment of the present invention. Fifth
Figures (,) are cross-sectional views of the vicinity of the photoelectric conversion element where strong spot light is incident, and Figures 6 (b), (C), (d
) is its schematic potential diagram. Reference numeral 13 denotes a photoelectric conversion element consisting of a PN junction photoder and an diode, 14 a transfer electrode of a charge transfer element array, and 15 a buried layer. 1
Reference numeral 6 denotes a transfer electrode that transfers the charge of the -PN junction photodiode to the buried layer 15 of the charge transfer element array.

The method of driving the solid-state imaging device of this embodiment will be explained below.
First, before the sweep drive is performed, charges overflow to the charge transfer element array from the PN junction photodiode on which light exceeding the saturation exposure amount is incident (FIG. 6(b)).

Next, by partially opening the transfer electrode, a portion of the saturated charge is sent to the charge transfer element array (FIG. 6(C)). In the next period, the transfer electrode 16 closes, so the PN junction photodiode has more room to accumulate charge (see Fig. 5).
d)).

Therefore, charges will not overflow from the PN junction diode. If the sweep drive is performed within such a time, the influence of overflowing charges during the sweep drive as described above can be suppressed.

FIG. 6 shows an example of driving pulses for carrying out the method for driving a solid-state imaging device according to an embodiment of the present invention. φPT
is a pulsed charge added to the charge transfer element array to convert the charge of the photoelectric conversion element array to the saturation signal ρ before driving to sweep out the charge at time t1. It works like this. After this time t3. At t4, signal charges are sent to the storage region.

In this example, when an operation was performed in which half of the charge stored in the photoelectric conversion element was discarded during sweeping and the remaining half was treated as a signal charge, the amount of light that appeared as a white vertical line was reduced compared to the conventional operation. The effect of the present invention was significant, with an improvement of about 20 times.

In this embodiment, a part of the saturated signal charge of the photoelectric conversion element array is discarded before the sweep drive, but the electrodes that transfer the charges of the photoelectric conversion element array to the charge transfer element array are used until the sweep drive is performed. When the PT is opened and the sweeping drive is performed,
This method has high industrial value as it can effectively eliminate the blooming phenomenon that could not be prevented with conventional methods of closing the PT awakening pole.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a charge transfer solid-state imaging device, Figure 1-2 is a diagram of applied clock pulses for implementing a conventional driving method for a solid-state imaging device, and Figure 3 is a diagram showing image quality degradation caused by the conventional driving method. Figure 4 is a schematic diagram of the photoelectric conversion element and its surroundings on which a saturated exposure amount of light enters to explain the pluming phenomenon that occurs in the conventional driving method, and Figure 5 (, ) is a diagram of the main part. FIG. 6(b) is a sectional view of a main part of a solid-state imaging device for implementing the driving method of the invention.
, (C) and (d) are schematic potential diagrams for explaining the driving method of the solid-state imaging device in one embodiment of the present invention, and FIG. 6 is a driving diagram for implementing the driving method of the solid-state imaging device of the present invention. FIG. 3 is a diagram showing one example of pulses. 1o...Transfer electrode, 11...Charge transfer element array in storage region, 17...Buried layer, 18
...Channel stopper, 19Φ...
Light shielding film, 2o...Semiconductor substrate, 21...
・・Potential under the transfer electrode 14, 23・・e・− Potential under the transfer electrode 16, 24・・・・・Potential of a part of the channel stopper, 26・・・・・・・Saturation of the photoelectric conversion element part Charge, 26...Overflow charge, 27. , -...Overflow charge and charge discarded by photoelectric conversion element, 28...Signal charge, 29
...Charge thrown away by the photoelectric conversion element, 30...
...Potential when the transfer electrode 16 is partially opened. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 31. l Figure 4 mouth【】-/l Figure 5

Claims (1)

[Claims] In a solid-state imaging device having an imaging area including a photoelectric conversion element array and a charge transfer element array on the same semiconductor substrate, after performing an operation to sweep out a portion of the saturated charges of the photoelectric conversion element array, the photoelectric conversion element A method for driving a solid-state imaging device, characterized by performing an operation associated with reading out signal charges in a column.