JPH03195185A - Driving method for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To stablize a read operation by impressing a pulse, whose polarity is reverse to that of a charge read pulse, to a shielding electrode when the signal charge of a photosensitive part is read out to a charge transfer part. CONSTITUTION:A second conductive well 12 is formed on a first conductive semiconductor base 11 and in the second conductive well 12, a photosensitive part 13 composed of a first conductive area, charge transfer part 14 composed of the first conductive area, and charge read part 15 composed of a second conductive area between the photosensitive part 13 and the charge transfer part 14 are provided. By a solid-state image pickup element equipped with a charge read electrode 18, for which the charge read pulse is impressed, and a shielding electrode 19 having an opening at the photosensitive part on the semiconductor base 11, the pulse, whose polarity is reverse to that of the charge read pulse, synchronized with this charge read pulse is impressed to the shielding electrode 19. Thus, since the motion of the signal charge can be accelerated and the charge read operation can be accelerated as well, a picture degrading phenomenon such as an after image, etc., can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a solid-state image sensor, and more particularly to a method for driving a solid-state image sensor when reading signal charges from a photosensitive portion to a charge transfer region.

[Prior Art] FIG. 4 is a sectional view of a unit cell portion of a commonly used CCD solid-state image sensor. In the figure, 11 is an n-type semiconductor substrate, 12 is a p-well made of an n-type semiconductor formed in the substrate, 13 is a photosensitive part made of an n-type semiconductor, and 14 is an n-type semiconductor substrate.
15 is a charge readout section made of an n-type semiconductor and is provided between the photosensitive section 13 and the charge transfer section 14; 16 is a charge transfer section made of a type semiconductor; 16 is a charge transfer section made of an n-type semiconductor;
・N17 is an oxide film, 18 is a charge readout electrode, and one is a light-shielding electrode to prevent light from entering other than the photosensitive area 13.

Next, a conventional method for driving the above-mentioned solid-state image sensor will be explained.

FIG. 5 is a waveform diagram of voltages applied to the charge readout electrode 18 and the light shielding electrode 19 when reading charges from the photosensitive section 13 to the charge transfer section 14. In the figure, period b is a charge accumulation period, and during this period, the charge readout voltage [i18
O[V] is applied to the light-shielding electrode]9, and 25[V] is applied to the light-shielding electrode]9.

Further, period a is a charge readout period in which signal charges accumulated in the photosensitive section 13 are read out to the charge transfer section 14, and during this period, a charge readout voltage of 14.5 [V] is applied to the charge readout electrode 18. However, 1.25 [■], which is the same as in period b, continues to be applied to one light-shielding electrode.

FIG. 6 is a one-dimensional potential diagram of the X-X' interface in FIG. 4, where the solid line shows the potential distribution during the charge readout period, and the broken line shows the potential distribution during the storage period.

[Problems to be Solved by the Invention] In the conventional charge readout method described above, when the charge readout voltage is applied to the charge readout electrode 18, as shown by the solid line in the sixth Not only that, but the potential of the photosensitive section 13 is also raised at the same time.
An electric field is no longer formed between the photosensitive section 13 and the charge readout section 15. Therefore, in the conventional driving method, the signal charges move only by diffusion, resulting in a long readout time and a large afterimage.

[Means for Solving the Problems] In the method for driving a solid-state imaging device of the present invention, a second conductivity type well is formed in a first conductivity type semiconductor substrate, and a first conductivity type region is formed in the second conductivity type well. A photosensitive section consisting of a semiconductor substrate, a charge transfer section consisting of a first conductivity type region, and a charge readout section consisting of a second conductivity type region between the photosensitive section and the charge transfer section are provided, and charges are transferred onto the semiconductor substrate. A method for driving a solid-state imaging device including a charge readout electrode to which a readout pulse is applied and a light-shielding electrode having an opening in a photosensitive portion, the method comprising:
A pulse of opposite polarity to the charge readout pulse is applied to the light shielding electrode in synchronization with the charge readout pulse.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a pulse waveform diagram of a voltage applied to a charge reading electrode 18 and a light shielding electrode 19 when reading charges from a photosensitive section 13, explaining one embodiment of the present invention. Light shielding electrode 1
A pulse voltage of 1.25 [V] during normal operation and -10 [V] during charge readout is applied to electrode 9 in synchronization with charge readout electrode 18 .

Figure 2 shows the fourth wave when the pulse voltage as described above is applied.
It is a one-dimensional potential distribution diagram of the x-x' interface in the figure.

As shown by the broken line in the figure, the potential distribution during the accumulation period (period 19) is similar to that of the conventional example, but as shown by the solid line in the figure, the potential distribution is 1E during the charge readout period (period a). Even if a charge readout voltage of 14°51V] is applied to the charge readout electrode 18, the light shielding electrode 1
8 is applied with a voltage of -10 [V], the photosensitive portion 13 is affected by the light-shielding electrode 18 and is fixed at a lower potential than the conventional one. Therefore, an electric field can be formed in the photosensitive section 13 and the charge reading section 15, and the movement of charges can be made faster.

FIG. 3 shows a photosensitive section 13 illustrating another embodiment of the present invention.
2 is a pulse waveform diagram of the voltage applied to the charge readout electrode 18 and the light-shielding electrode 19 when reading out the charge from the cell. FIG. In this embodiment, the pulse voltage applied to the light-shielding electrode 19 is raised 11 times earlier than the pulse voltage applied to the charge readout electrode 18, and is brought down t2 later than the pulse voltage applied to the charge readout electrode 18. By applying such a pulse, the potential of the photosensitive portion 13 can be more stabilized and fixed, so that the read operation can be made more stable than in the previous embodiment.

[Effects of the Invention] As explained above, the present invention applies a pulse of opposite polarity to the charge readout pulse to the light-shielding electrode when reading the signal charge of the photosensitive part to the charge transfer part. According to the invention, it is possible to fix the potential of the photosensitive section when reading charges, and to form an electric field between the photosensitive section and the charge reading section.

Therefore, according to the present invention, the movement of signal charges can be made faster and the charge readout operation can be made faster, so that image deterioration phenomena such as afterimages can be suppressed.

[Brief explanation of drawings]

1 and 3 are pulse waveform diagrams for explaining the present invention in detail, FIG. 2 is a potential distribution diagram in an embodiment of the present invention, and FIG. 4 is a cross-sectional diagram of a solid-state imaging device. , FIG. 5 is a pulse waveform diagram of the conventional example, and FIG. 6 is a potential distribution diagram of the conventional example. 11...n type semiconductor substrate, 12...p well, 1
3... Photosensitive section, 14... Charge transfer section, 15...
・Charge reading section, 16... Channel stopper,
17... Oxide film, 18... Charge readout electrode, 1... Light shielding electrode.

Claims (1)

[Claims] A photosensitive part and a charge transfer part in the surface area of the semiconductor substrate,
A charge readout section for reading signal charges from the photosensitive section to the charge transfer section is provided, and a charge readout electrode to which a charge readout pulse is applied is provided on the semiconductor substrate through an insulating film, and a charge readout electrode is provided on the photosensitive section. A method for driving a solid-state imaging device provided with a light-shielding electrode having an aperture, the method comprising: applying a pulse of opposite polarity to the charge readout pulse in synchronization with the charge readout pulse to the light-shielding electrode. Driving method.