JPH08264746A - Drive method for solid state image sensor - Google Patents

Abstract

PURPOSE: To obtain a drive method for a solid state image sensor in which the fixed pattern noise, caused by the fluctuation in the difference of the quantity of charges being read out, can be reduced along with the capacitive residual image. CONSTITUTION: A reverse bias is applied between a charge storing section 19 and a semiconductor substrate and bias charges are injected directly into the charge storing section 19 by the reverse current thus partially resetting the bias charges to a charge transfer section 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device used in a television camera or the like, and more particularly to a method of driving a solid-state image pickup device for performing bias charge injection / discharge operations to / from a charge storage section.

[0002]

2. Description of the Related Art In recent years, a charge coupled device (CC) is provided in a signal scanning section as an image pickup apparatus for a broadcast camera, a home video movie or the like.
Solid-state imaging devices using D) are widely used. In addition, recently, a solid-state imaging device having a two-story structure in which a photoelectric conversion film is laminated on a light receiving region has been developed. The solid-state image pickup device of the photoconductive film laminated type of the two-story structure has an excellent feature that it can maintain high sensitivity even in a minute pixel, and is most expected as an image pickup device of a camera for optical definition television. There is.

By the way, the photoconductive film laminated type solid-state image pickup device has a problem that a capacitive afterimage which deteriorates the characteristics of the element occurs. The capacitive afterimage occurs because the signal charge accumulated in the pixel cannot be completely read out, and deteriorates the image particularly in low illuminance. Therefore, in order to eliminate this capacitive afterimage, the following driving method is usually adopted.

FIG. 4 is a schematic plan view of the solid-state image pickup device.
The signal charge in the charge storage section 15 formed in the pixel region 12 is read out to the charge transfer section 14, and then the memory section 1
3 is transferred to the digital camera 3, passed through the horizontal CCD 10 according to the TV signal format, detected by the charge detector 11, and output as an electric signal. On the other hand, in order to eliminate the capacitive afterimage,
Bias charges are injected from the charge injection / discharge diode 1 into the charge storage unit 15 through the charge transfer unit 14. By resetting the injected bias charge and afterimage charge from the charge storage section 15 to the charge transfer section 14, the capacitive afterimage is reduced.

FIG. 5 is a sectional view of the pixel portion taken along the line AA 'in FIG. In the photoconductive film stack type solid-state imaging device, incident light passes through the transparent electrode 25 and is photoelectrically converted within the photoelectric conversion film 24, and is accumulated in the charge accumulating portion 19 as a signal charge through the pixel electrode 23 and the extraction electrode 21. It This signal charge is read out to the charge transfer unit 18 by turning on the transfer gate 20, and sequentially transferred in the charge transfer unit 18. Each pixel is formed on the semiconductor substrate 16 and is separated by the element separation region 17. Bias charge is shown in Figure 6.
Is injected and reset as shown in the potential diagram of FIG. The shaded area in the figure indicates the presence of electric charges.
First, immediately after the signal charge is transferred, there is only the residual charge 27 in the charge storage unit 19 as shown in FIG. 6A. After that, the bias charge 28 is passed through the charge transfer unit 18.
Is injected into the charge storage portion 19 (FIG. 6B). The injected bias charge 28 is reset from the charge storage unit 19 to the charge transfer unit 18 (FIG. 6C). At this time, the residual charge 28 of the bias charge remains in the charge transfer unit 18. However, when the bias charge 28 remains in the charge transfer portion as described above, the potential of the charge read gate 26 easily fluctuates as shown in FIG. 7, and it varies from pixel to pixel. Due to this potential variation 29, the variation 30 of the bias charge 28 left in the charge storage section 19 also becomes large, and this appears as fixed pattern noise. Further, FIG. 8 schematically shows a timing chart of the transfer gates 2 to 5, the injection diode 1, and the transparent electrode 25 when the operation of FIG. 6 is performed.

[0006]

As described above, in the conventional method for driving the solid-state image pickup device, when the bias charge is reset, a large variation occurs in the amount of charge left in the charge storage section for each pixel, and therefore, an image is not displayed. There was a problem that fixed pattern noise was generated.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for driving a solid-state image pickup device capable of reducing fixed pattern noise caused by variations in the amount of read charges. To provide.

[0008]

The essence of the present invention is to directly inject the bias charge into the charge storage section without interposing the charge transfer section. That is, according to the present invention, a voltage in a reverse bias state is applied between the charge storage portion and a semiconductor substrate, an element isolation portion, or other anticonducting semiconductor region, and a bias current is applied to the charge storage portion by a reverse current. To inject.

[0009]

According to the present invention, since the bias charge can be directly injected into the charge storage section without passing through the charge transfer section, there is no residual charge in the charge transfer section when the bias charge is reset. It is possible to reduce variations in the bias charges left in the storage section, and it is possible to reduce fixed pattern noise.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the injection and reset operation of bias charges according to the present invention. The structure will be described with reference to FIGS. 4 and 5 described in the related art. First, immediately after the signal charges are transferred, as shown in FIG.
There is only a residual charge 27 in the. Then, for example,
The semiconductor substrate 2 is formed on the transparent electrode 25 in FIG.
By applying a positive voltage to the charge storage unit 6,
9B, a reverse bias is applied between the semiconductor substrate 26 and the semiconductor substrate 26, and the bias charge 28 is injected into the charge storage portion 19 by the reverse current. The injected bias charges 28 are reset from the charge storage unit 19 to the charge transfer unit 18.
(C). At this time, no residual charge remains in the charge transfer unit 18. Therefore, unlike the conventional case, as shown in FIG. 2, when the bias charge 28 is reset to the charge transfer unit 18, the potential of the charge read gate 26 is unlikely to change. Since this variation 31 is small, the variation 32 of the bias charge left in the charge storage section 19 is small, and fixed pattern noise can also be reduced. Further, FIG. 3 schematically shows a timing chart of the transfer gates 2 to 5, the injection diode 1, and the transparent electrode 25 when the same operation as that shown in FIG. 6 of the prior art is performed.

[0011]

As described above, according to the present invention, in order to inject the bias charge into the charge storage portion without directly passing through the charge transfer portion, the bias charge is injected at the time of resetting and resetting. It is possible to reduce the fixed pattern noise that was used.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an operating potential of a solid-state image sensor according to the present invention.

FIG. 2 is a conceptual diagram of the potential of the solid-state image sensor according to the present invention when resetting.

FIG. 3 is a pulse waveform diagram for driving a solid-state image sensor according to the present invention.

FIG. 4 is a plan view of a solid-state image sensor.

FIG. 5 is a sectional view of a stacked solid-state imaging device cell.

FIG. 6 is a conceptual diagram of a conventional solid-state imaging device operating potential.

FIG. 7 is a conceptual diagram of a potential during a reset operation of a conventional solid-state image sensor.

FIG. 8 is a conventional solid-state image sensor drive pulse waveform diagram.

[Explanation of symbols]

 1 Bias Charge Injection / Ejection Diodes 2-5, 6-9 Charge Transfer Gate 10 Horizontal CCD 11 Charge Detector 12 Pixel Region 13 Memory Section 15 Unit Cell 16 Semiconductor Substrate 17 Element Separation Section 18 Charge Transfer Section 19 Charge Storage Section 20 Charge Transfer gate 21 Extraction electrode 22 Insulating film 23 Pixel electrode 24 Photoelectric conversion film 25 Transparent electrode

Claims (2)

[Claims] 1. Injecting a bias charge into a charge storage part,
A driving method of a solid-state imaging device, in which a part of the injected bias charge is reset and discharged to a charge transfer unit, and thereafter, a signal is accumulated in a charge accumulating unit for a fixed time and the accumulated signal and the charge are read out together with the bias charge. In the above, in the method, a reverse bias is applied between the charge accumulating portion and the charge accumulating portion and a semiconductor device region of anti-conduction type, and a reverse current is caused to flow to inject bias charge into the charge accumulating portion. And
Driving method of solid-state imaging device. 2. In order to apply a reverse bias between the charge accumulating portion and the charge accumulating portion and an anti-conduction type semiconductor element region, a pixel electrode electrically connected to the charge accumulating portion is applied. The method for driving a solid-state imaging device according to claim 1, wherein the method is performed by applying an electric pulse to an electrode electrically coupled through a photoelectric conversion film.