JP2903008B2 - Driving method of solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid-state imaging device having a virtual phase electrode structure, and more particularly, to a driving method for enabling an electronic shutter operation in the solid-state imaging device.

[0002]

2. Description of the Related Art A CCD solid-state image sensor widely used in an image pickup device such as a television camera has a plurality of transfer electrodes formed in parallel on a semiconductor substrate and transfers information charges generated inside the substrate by photoelectric conversion. It is configured to accumulate and transfer in a channel region formed by the electrode. In such a solid-state imaging device, a virtual phase electrode structure has been considered as one of the methods for simplifying the electrode structure and the driving clock. This virtual phase electrode structure, for example,
IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. ED-28.
PP483〜489. May 1981 "Virtual-Phase Technology: AN
ew Approach to Fabrication of Large Area CCD's ".

FIG. 3 shows a CCD having a virtual phase electrode structure.
It is sectional drawing of a solid-state image sensor. On the surface of the silicon substrate 1, a plurality of transfer electrodes 3 are arranged at regular intervals via an oxide film 2. On the surface of the silicon substrate 1 in the gap between the transfer electrodes 3, a diffusion region 4 in which impurities are implanted at a high concentration is formed. The diffusion region 4 fixes a potential in the substrate, and sets a virtual phase electrode. Further, a barrier region 5 into which impurities are further implanted is formed in a part of the substrate region below the transfer electrode 3 and a part of the diffusion region 4. The barrier region 5 forms a step in the potential near the surface of the silicon substrate 1 and prevents the transfer of information charges in the reverse direction.

A single-phase transfer clock φ1 is applied to each of the plurality of transfer electrodes 3, and the potential in the silicon substrate 1 periodically fluctuates in response to the transfer clock φ1. Thereby, the information charges generated in the silicon substrate 1 are transferred and output in a certain direction according to the action of the potential formed by each transfer electrode 3. The variation of the potential depth in the silicon substrate 1 due to the transfer clock φ1 is as follows.
It is configured such that the depth of the potential set in the diffusion region 4 becomes an intermediate point. That is, the impurity concentration of the diffusion region 4, the potential of the transfer clock φ1, and the like are set so that a deeper potential and a shallower potential can be formed with respect to the potential having a constant depth formed by the diffusion region 4. . Then, due to the action of the barrier region 5, a step is formed in the potential formed in the region below the transfer electrode 3 and in the diffusion region 4 so as to become deeper in the transfer direction. Therefore, when the potential under the transfer electrode 3 is changed from a state deeper than the potential of the diffusion region 4 to a shallow state, the information charges accumulated under the transfer electrode 3 are efficiently transferred to the diffusion region 4 adjacent to the output side. Well transferred.

According to the solid-state imaging device having such a virtual phase electrode structure, since information charges can be transferred by single-phase driving, the configuration of a drive circuit for generating the transfer clock φ1 can be simplified. In addition, since a region where the surface of the silicon substrate 1 is exposed from between the transfer electrodes 3, that is, an opening can be provided widely, light from a subject can be efficiently taken into the silicon substrate 1 and light receiving sensitivity can be improved. Can be improved.

By the way, in a case where a large amount of light irradiates the solid-state imaging device and information charges exceeding the storage capacity are generated in each light receiving pixel, excess information charges are discharged to the outside of the light receiving pixels to be adjacent thereto. A measure (blooming suppression) for preventing the influence on the pixel is taken. As a method of suppressing blooming, it has been conventionally used to provide an overflow drain for absorbing excess charge adjacent to a light receiving pixel. However, in such a method, light cannot be received at the overflow drain portion, and light receiving efficiency is reduced. In recent years, a so-called vertical overflow drain method of discharging excess charges to the substrate side has been used. It is in. This vertical overflow drain method uses the inside of a substrate on which light receiving pixels are formed as a drain for discharging electric charges. A P type diffusion region is formed on an N type silicon substrate, and the light receiving pixels are formed in the diffusion region. Is formed.

[0007]

In a vertical overflow drain type solid-state image pickup device, an electronic shutter for discharging the accumulated information charges and then newly accumulating the information charges in the process of accumulating the information charges. Is adopted. In the electronic shutter operation, the potential applied to the transfer electrode 3 and the potential applied to the silicon substrate 1 are controlled to eliminate the potential barrier on the silicon substrate 1 side in a region below the transfer electrode 3. .

However, in the case of the solid-state imaging device having the above-described virtual phase electrode structure, the potential of the diffusion region 4 cannot be controlled, so that it is difficult to employ the vertical overflow drain method. Therefore, the advantages of the solid-state imaging device having the virtual phase electrode structure, such as high light-receiving efficiency and suitable for high density, cannot be fully utilized. Accordingly, it is an object of the present invention to adopt a vertical overflow drain method for a solid-state imaging device having a virtual phase electrode structure and to enable an electronic shutter operation.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is characterized by a surface of a semiconductor substrate having an overflow drain therein for absorbing excess charges. A plurality of channel regions are arranged near each other in parallel with each other, extend in a direction intersecting the channel regions, and have a plurality of first electrodes parallel to each other and a second electrode covering the plurality of first electrodes. A method for driving a solid-state imaging device formed on a semiconductor substrate, wherein a first potential for forming a potential of the channel region at a first depth and a potential of the channel region are set to the first potential.
And a second potential formed at a second depth greater than the depth of the first electrode is applied to the plurality of first electrodes at a constant period,
At the time of driving the transfer of the information charges, a third potential which forms the potential of the channel region between the first depth and the second depth is applied to the second electrode, and the information charges are discharged. In driving, a fourth potential for forming the potential of the channel region shallower than the first depth is to be applied to the second electrode.

According to the invention, the potential of the substrate region between the first electrodes is controlled by the second electrode, and between two potential depths formed by the first electrode, or It is formed shallower than the potential depth that can be formed by the first electrode. Therefore, at the time of transferring the information charges, the information charges in the channel region below each transfer electrode are sequentially transferred to the channel region below the next-stage transfer electrode through the channel region between the transfer electrodes. When the information charges are discharged, the information charges in the channel region below each transfer electrode are discharged from the channel region to the substrate when the information charges are transferred to the channel region between the transfer electrodes.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In describing a method for driving a solid-state imaging device according to the present invention, first, the structure of a solid-state imaging device to which the present invention is applied will be described. FIG. 3 is a cross-sectional view of a solid-state imaging device having a virtual phase electrode structure to which the present invention is applied.
Transfer electrodes 12 made of polycrystalline silicon are arranged in parallel on a silicon substrate 10 with a certain interval via an oxide film 11. The transfer electrode 12 is provided in a direction crossing a plurality of channel regions formed on the surface of the silicon substrate 10, and controls a potential state in the channel region. A barrier region 13 having an impurity concentration different from that of the channel region is formed in a partial region of the surface of the silicon substrate 10 below the transfer electrode 12, and a step is formed by the transfer electrode 12 in the depth of the potential formed in the channel region. Is caused. Further, a transparent electrode 14 is formed on the transfer electrode 12 so as to overlap the entire surface of the transfer electrode 12 via the oxide film 11. The transparent electrode 14 only needs to be transparent to incident light, and ITO (indium tin oxide), ZnO (zinc oxide), or the like can be used.

FIG. 1 is a potential diagram for explaining a method of driving a solid-state imaging device according to the present invention. These potentials are controlled by two-phase transfer clocks φ1 and φ2 applied to each transfer electrode 12 and a constant control voltage VC applied to the transparent electrode 14. When the information charges accumulated in the channel region are transferred and driven, the potential change formed in the channel region below the transfer electrode 12 is set such that the potential of the channel region between the transfer electrodes 12 is the center point. , The potentials of the control voltage VC and the transfer clocks φ1 and φ2 are set. That is, when the potential formed in the channel region below the transfer electrode 12 changes from a deep state to a shallow state due to inversion of the transfer clocks φ1 and φ2, the potential exceeds the potential of the channel region between the transfer electrodes 12. The control voltage VC is set so as to be shallow.
Thereby, the information charges in the channel region below the transfer electrode 12 are transferred to the channel region between the transfer electrodes 12. Further, the transfer electrodes 1 and 2 are inverted by transfer electrodes 1 and 2 respectively.
The control voltage VC is set such that when the potential formed in the channel region below 4 changes from a shallow state to a deep state, the potential becomes deeper than the potential of the channel region between the transfer electrodes 12. . Thereby, the information charges in the channel region between the transfer electrodes 12 are transferred to the channel region below the transfer electrode 12. Thus, by repeating the inversion operation of the transfer clocks φ1 and φ2, the information charges in the channel region are sequentially transferred to the output side along the channel region.

On the other hand, in the case of the drive for discharging unnecessary information charges, a potential shallower is formed in the channel region between the transfer electrodes 12 than in the channel region below the transfer electrode 12. Control voltage VC is set as described above. That is, the control voltage VC is set such that the potential formed between the transfer electrodes 12 by the action of the transparent electrode 14 is further shallower than the shallowest possible potential of the channel region below each transfer electrode 12. . As a result, even if the potential of the channel region under the transfer electrode 12 changes from a deep state to a shallow state due to the inversion operation of the transfer clocks φ1 and φ2, the information charges under the transfer electrode 12 It is not transferred to the channel region but is discharged to the silicon substrate 10 side. According to such an operation of discharging the information charges, an electronic shutter operation for discharging the information charges accumulated so far in the middle of the accumulation period becomes possible.

[0014]

According to the present invention, the vertical overflow drain method can be adopted for the solid-state image pickup device having the virtual phase electrode structure, and the electronic shutter operation can be performed with higher efficiency.
Therefore, the solid-state imaging device can be effectively utilized without deteriorating the advantages of the virtual phase electrode structure.

[Brief description of the drawings]

FIG. 1 is a timing chart illustrating a method for driving a solid-state imaging device according to the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of a solid-state imaging device to which the present invention is applied.

FIG. 3 is a cross-sectional view illustrating a structure of a conventional solid-state imaging device.

[Explanation of symbols]

 1, 10 Silicon substrate 2, 11 Oxide film 3, 12 Transfer electrode 4 Diffusion region 5, 13 Barrier region 14 Transparent electrode

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-246971 (JP, A) JP-A-2-105571 (JP, A) JP-A-60-260154 (JP, A) JP-A-2- 274184 (JP, A) JP-A-3-135070 (JP, A) IEEE TRANSACTIONS ON ELECTRON DEVIC ES, VOL. ED-28, NO. 5, MAY 1981, p. 483-489 (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/30-5/335

Claims (2)

(57) [Claims] 1. A plurality of channel regions are arranged near a surface of a semiconductor substrate having an overflow drain for absorbing excess charge therein, and a plurality of first regions extending in a direction intersecting with the channel regions and parallel to each other. And a second electrode transparent to incident light covering the plurality of first electrodes is formed on the semiconductor substrate. In the method for driving a solid-state imaging device, the potential of the channel region is set to the first potential. A first potential formed at a depth and a second potential formed at a second depth greater than the first depth are applied to the plurality of first electrodes at a constant period. And a third potential for forming a potential of the channel region between the first depth and the second depth at the time of driving the transfer of the information charge, to the second electrode, Information A driving method for a solid-state imaging device, comprising: applying a fourth potential to the second electrode for forming the potential of the channel region to be shallower than the first depth when driving the discharge of the load. 2. The solid-state imaging device according to claim 1, wherein a single-phase or multi-phase transfer clock that repeats the first and second potentials is applied to the plurality of first electrodes. Method.