JPH0793417B2 - Solid-state imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a solid-state image pickup device having a CCD image pickup element, and particularly to a configuration for obtaining high resolution and low spurious signals with a small number of sampling points in a field. The present invention also relates to a CCD solid-state image pickup device having high sensitivity, low noise, and low afterimage.

[Prior Art] Conventionally, in order to reduce a false signal due to an image having a spatial frequency higher than the Nyquist limit, for example, (1) a photoconductive film is laminated to enlarge a pixel aperture equivalently (2) a lenticular lens There is a method in which the pixel opening is equivalently increased by using (3) the image sensor is vibrated to equivalently make the pixel opening larger than the pixel pitch.

However, with the methods (1) and (2), it is not possible to obtain an aperture larger than the pixel pitch, and there is a limit. Also (3)
However, the method described above has a drawback in that it becomes mechanically complicated and leads to loss of stability, which is a great advantage of the solid-state imaging device.

In addition, one of the driving methods for CCD image sensors is a field accumulation mode in which the combination of vertical two pixels is changed for each field and the sum signal is output to perform interlaced scanning. It is used for the purpose of reducing the vertical direction, and although the false signal in the vertical direction can be reduced, the horizontal direction is the same as the conventional one.

Further, in order to limit and reduce the band of the false signal by post-processing, considering the characteristics of the filter obtained at present, a considerably large number of pixels are required, and not only the problem that the processing accuracy and the yield decrease, At the same time as the saturation signal amount and the sensitivity decrease due to the reduction of the pixel area, the noise also increases with the increase of the clock frequency (widening of the band), which causes a problem that the dynamic range significantly decreases.

As a solution to some of the above problems, at least the problem of false signals, the present applicant has already filed Japanese Patent Application No. 59-254219.
No. "Solid-state imaging device" was filed. According to this, it is possible to reduce the false signal without impairing the stability and the dynamic range of the CCD image pickup device. However, in this solid-state imaging device, since the light receiving and signal charge accumulating portion and the transfer electrode for transferring are separately provided, the aperture ratio related to the sensitivity is reduced, or the manufacturing process has a complicated laminated structure or the like. Had to be used.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of the related art, effectively enlarges the pixel aperture, eliminates false signals in the vertical and horizontal directions, and has a high resolution and sensitivity with a simple device configuration. It is an object of the present invention to provide a solid-state imaging device that has the above-described characteristics and that can reduce noise and obtain high-quality images with little afterimage.

[Means for Solving Problems] In order to achieve such an object, a solid-state image pickup device of the present invention has a frame transfer type solid-state image pickup device including an electrode group in each of a plurality of fields. The individual electrodes of the belonging electrode group are arranged corresponding to the pixels in the same field, and each electrode is arranged so as to be surrounded by the electrodes belonging to other fields.

Further, the solid-state imaging device of the present invention is a solid-state imaging device including a plurality of sets of electrodes, wherein the plurality of sets of electrodes are arranged corresponding to the positions of the respective light receiving elements, and at this time, are arranged adjacent to each other. Make sure that the electrode groups that are not connected together are not commonly connected, and that when the signal charge is stored, the part of the specific light receiving element surrounded by the adjacent light receiving elements becomes the charge storage part that collects the charges from the adjacent light receiving elements. The electric potential of the specific electrode group corresponding to the position of the light receiving element is set to be higher or lower than the electric potential of the electrode group corresponding to the position of the adjacent light receiving element.

Furthermore, the solid-state imaging device of the present invention prevents a charge turbidity from being formed by a plurality of electrode groups commonly connected to each other for performing both signal charge storage and transfer of the stored charge or only signal charge storage. In the solid-state imaging device including the isolation means for performing the above-mentioned operation, a plurality of sets of electrode groups are arranged corresponding to the positions of the respective light receiving elements, and at this time, the electrode groups arranged adjacent to each other are commonly connected. When the signal charge is accumulated, the position of the specific light receiving element surrounded by the adjacent light receiving elements corresponds to the position of the specific light receiving element so that it becomes a charge accumulation part that collects the charges from the adjacent light receiving elements. The potential of the specific electrode group is set to be higher or lower than the potential of the electrode group corresponding to the position of the adjacent light receiving element, the isolation means is inactivated, and the isolation means is set at the time of charge transfer. It is operated, wherein the accumulated charge collected at different positions for each of the plurality of sets of electrode groups which are commonly connected is to not cause turbidity in the other.

[Operation] According to the present invention, by making the pixel aperture larger than the pixel pitch, it is possible to reduce a false signal due to an image having a spatial frequency equal to or higher than the Nyquist limit without increasing the number of pixels. Even if the number of pixels is small, the resolution is reduced by using a checkerboard-like interpolation arrangement.
It is possible to achieve a sufficient resolution in the vertical and horizontal directions while keeping it in the diagonal direction, which is not so noticeable visually. Also,
As the number of pixels decreases, the saturation signal amount can be increased, and at the same time, the transfer clock frequency can be reduced. Therefore, noise can be reduced and the dynamic range can be expanded. Furthermore, by reading out all charges for each field, it is possible to achieve high sensitivity without wasting the amount of information, and it is possible to eliminate afterimages due to unread signals.

[Embodiment] FIG. 1 shows a pixel arrangement pattern of a frame transfer CCD image pickup device as a first embodiment for explaining the configuration of the solid-state image pickup device of the present invention. In the figure, 1, 2, and 3 indicate sample points (pixels) in each field, and each sample point is surrounded by sample points belonging to other fields in order to realize high resolution with a small number of pixels. It has a checkerboard-like interpolation arrangement. Each sample point is formed by a photo sensor using a photodiode or a MOS sensor. In the conventional method, even if the aperture ratio of the photo sensor is set to 100%, it is not possible to exceed the aperture in the range delimited by the solid line, but in the present invention, the pixel aperture is expanded to the range shown by the dotted line 5 as will be described later. It is what makes it possible to do.

FIG. 2 shows a transfer electrode pattern for realizing the configuration and operation of FIG. 11,12,13 are photosensors 1,2,3
11 are the first phase, and 12, 1 are the transfer electrodes respectively corresponding to
Reference numeral 3 has a three-phase electrode configuration of the second and third phases, respectively.
Note that FIG. 2 shows a simplified structure, and in the case of a front-illuminated type in which light is incident from the electrode side, a translucent conductive material or a perforated material using polycrystalline silicon, a metal oxide film, or the like is used. The structure or a combination thereof is used as an electrode. Further, when the substrate is made into a thin piece and a back-incidence type in which light is incident from the substrate side is used, a translucent electrode becomes unnecessary.

Figure 3 shows an example of the structure of a back-thinned frame transfer CCD as an example. FIG. 3 shows a part of a cross section taken along the line AA of FIG. In the figure, 21 is, for example, p
-Si, 22 are transfer electrodes made of SiO ₂ , and 11, 12, 13 are transfer electrodes made of polycrystalline silicon, respectively. The wiring is shown in a simplified manner.
A CCD having such a structure can be manufactured by a usual LSI manufacturing method.

FIG. 4 shows an example of the timing of the drive pulse applied to the electrode group of FIG. 2, and the operation of the first embodiment of the present invention will be described in detail. For the sake of convenience of explanation, it is assumed that the higher the applied potential, the lower the potential for the signal charge.

When capturing the first field, first keep the first phase at a high potential,
The region under the electrode 11 is set in the accumulation state. At this time, since the other electrodes are kept at a low potential, the photoelectrically converted signal charges are collected under the high-potential first-phase electrode as shown by the arrow in FIG. As a result, all the signal charges on the image pickup surface are accumulated under the electrode 11, and the pixel aperture in the area indicated by the dotted line 5 in FIG. 1 can be effectively obtained. In FIG. 1,
Although the movement of the charge is shown only for one pixel 1, such movement occurs over the entire image pickup surface.

During the next transfer period, first, the second phase is set to a high potential, and sequentially by the transfer clocks of the three phases, the storage unit (not shown) configured adjacent to the image pickup unit is operated by the movement shown by the dotted arrow in FIG. ) Is transferred to the signal charge). After all the signal charges have been transferred to the storage section, the imaging section starts imaging the second field.
In this case, the photoelectrically converted signal charges are moved to a lower portion of the second-phase electrode 12 to which a high potential is applied during the accumulation period in a direction different from that in the first field and accumulated, and then transferred to the accumulation unit. To be done. By similarly performing imaging in the third field, it is possible to read out all the photoelectrically converted signal charges in each field, and it is possible to effectively enlarge the pixel aperture at all sampling points.

During the transfer period, in order to prevent mixing of signal charges between transfer electrodes adjacent to each other along the transfer direction, impurities are diffused or thickened in the region of the channel stop 15 in FIG. 5 so as to form a deep buried channel. By using an oxide film, etc., the potential for the signal charge is set to an appropriate condition such that it is lower than the lower part of the electrode group other than the storage electrodes during the storage period and higher than all the electrodes when the transfer pulse is applied. . As a result, the diffusion of charges in the lateral direction is prevented and the charges can be transferred in the vertical direction during transfer without hindering the transfer of charges from under the surrounding electrodes to under the storage electrodes. .

Further, if polycrystalline silicon or the like is buried in the oxide film in the region of the channel stop 15 to serve as a channel stop electrode, and a bias voltage having the above-mentioned appropriate potential is applied in common to all of these electrodes, the transfer period is increased. It is easy to achieve the channel stop effect only in the inside.

Furthermore, instead of providing the above-mentioned channel stop region, a directional transfer electrode for limiting the transfer direction of charges formed by diffusing impurities in a part under the transfer electrode or applying a thick oxide film is used. Thus, it is possible to prevent signal charges in directions other than the transfer direction from being mixed with each other during charge transfer.

The embodiment of the frame transfer CCD image pickup device has been described above in detail. For example, a light-shielded transfer channel is provided in the region of FIG. 5 and a transfer gate is provided in the adjacent portion between this transfer channel and each pixel. Further, the effects of the present invention can be achieved even by using a CCD image pickup device having an interline transfer type configuration. In this case, the electrodes 11 to 13 of FIG.
Operates as storage electrodes corresponding to the photosensors 1 to 3 of FIG. 1, respectively. By applying a predetermined voltage to the storage electrodes during the storage period shown in FIG. 4, the photoelectrically converted signal charges are collected as shown by the arrow in FIG. 1, and effectively the dotted line 5 in FIG. It is possible to obtain a pixel aperture in the area of. The accumulated signal charge is sent to the transfer channel via the transfer gate within the horizontal blanking period, and then moved along the transfer channel to be read out. The next field is accumulated during the period from when the signal charge is sent to the transfer channel until it is read. In this way, by sequentially imaging each field, it is possible to realize a solid-state imaging device having high resolution, low false signal, high sensitivity, low noise, and low afterimage.

FIG. 6 shows a frame transfer type as a second embodiment of the present invention.
The arrangement pattern of the pixels of the CCD image sensor is shown. 101 ~ 104
Indicate sample points in each field, which are formed by photosensors as in the first embodiment. A sample point 101 is surrounded by sample points 102,1
As surrounded by 03 and 104, the sample points in each field are in a checkered pattern surrounded by the sample points in the other fields. In this embodiment, the effective pixel aperture can be expanded to the range shown by 105.

FIG. 7 shows the transfer electrode pattern of this embodiment. 111 ~ 114
Is a transfer electrode corresponding to each of the photosensors 101 to 104, 111 is a first phase, and 112 to 114 are second to fourth phase four-phase electrode configurations. The material and structure of the electrode and the light incident type are the same as those in the first embodiment.

FIG. 8 shows an example of the timing of the drive pulse applied to the electrode group of FIG. 7, and the operation of the second embodiment will be described.

At the time of the first field imaging, first, the first phase is set to a high potential, and the region under the electrode 111 is set in the accumulation state. At this time, since the other electrodes have a low electric potential, the photoelectrically converted signal charges are collected under the electrode 101 to which a high electric potential is applied as shown by the arrow in FIG. In the next transfer operation, first, the second phase is set to a high potential, and the signal charges are sequentially transferred to the accumulating section formed adjacent to the image pickup section by the movements shown by the dotted arrows in FIG. To be done. After all the signal charges have been transferred to the storage section, the imaging section starts imaging the second field. By performing imaging and transfer in the same manner for the third and subsequent fields, it is possible to read out all the signal charges for each field, and the dotted line 10 in FIG.
As shown in Fig. 5, the pixel aperture can be effectively enlarged.

In order to prevent the mixing of charges between the transfer electrodes adjacent to each other along the transfer direction, the portion 115 in FIG. 9 is used as a channel stop, or instead of this, a directional transfer electrode is used. The same effect can be obtained with the same configuration as that of the embodiment.

The embodiment of the frame transfer CCD image pickup device has been described above in detail. For example, by providing a light-shielded transfer channel in the region of FIG. With the above-mentioned configuration and the same operation as that of the first embodiment, the effect of the present invention can be obtained.

[Effects of the Invention] As described above based on the embodiments, according to the present invention, by making the pixel aperture larger than the pixel pitch, a false signal due to an image having a spatial frequency equal to or higher than the Nyquist limit can be generated. Can be reduced without increasing the number of pixels. At the same time, the checkerboard-like interpolation arrangement is used for the pixel arrangement. It is possible to realize sufficient resolution in vertical and horizontal directions. Further, since the saturation signal amount can be increased without decreasing the number of pixels and the transfer clock frequency can be reduced at the same time, noise can be reduced and the dynamic range can be expanded. Furthermore, by reading out all charges for each field, it is possible to achieve high sensitivity without wasting the amount of information, and it is possible to eliminate afterimages due to unread signals. In addition, since the structure is simple and restrictions on design rules can be reduced, processing accuracy and yield can be significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the arrangement of pixels and openings in one embodiment of the present invention, FIG. 2 is a diagram showing an electrode pattern used in the embodiment of FIG. 1, and FIG. 3 is the present invention. FIG. 4 is a schematic cross-sectional view showing the structure of the image pickup device of FIG. 4, FIG. 4 is a view showing timings of drive pulses applied to the electrodes, FIG. 5 is a view showing an electrode pattern including a channel stop, and FIG. FIG. 7 is a schematic diagram for explaining the arrangement of pixels and apertures in another embodiment of the invention, FIG. 7 is a diagram showing a pattern of electrodes used in the embodiment of FIG. 6, and FIG. 8 is a drive pulse applied to the electrodes. FIG. 9 is a diagram showing the timing of FIG. 9, and FIG. 9 is a diagram showing an electrode pattern including channel stops. 1,2,3 …… Pixel, 11,12,13 …… Electrode, 15 …… Channel stop, 101,102,103,104 …… Pixel, 111,112,113,114 …… Electrode, 115 …… Channel stop.

Claims (6)

[Claims] 1. In a frame transfer type solid-state imaging device having an electrode group in each of a plurality of fields, each electrode of the electrode group belonging to each field is arranged corresponding to a pixel in the same field, and A solid-state imaging device, wherein the electrodes are arranged so as to be surrounded by electrodes belonging to other fields. 2. A solid-state image pickup device comprising a plurality of sets of electrode groups, wherein the plurality of sets of electrode groups are respectively arranged corresponding to the positions of the respective light receiving elements, and at this time, the electrode groups arranged mutually are common. When the signal charge is accumulated, the position of the specific photodetector surrounded by the adjacent photodetectors becomes a charge accumulating part that collects the charges from the adjacent photodetectors. The solid-state imaging device is characterized in that the potential of the specific electrode group corresponding to is set to be higher or lower than the potential of the electrode group corresponding to the position of the adjacent light receiving element. 3. A plurality of sets of electrode groups connected in common for performing both signal charge storage and transfer of the stored charge, or only signal charge storage, and isolation means for preventing charge turbidity. In the solid-state imaging device including, the plurality of sets of electrode groups are respectively arranged corresponding to the positions of the respective light receiving elements, and at this time, the electrode groups arranged adjacent to each other are connected together in common. When the signal charge is accumulated, the specific light receiving element surrounded by the adjacent light receiving elements becomes a charge accumulating portion that collects the charges from the adjacent light receiving elements. The potential of the electrode group is set to be higher or lower than the potential of the electrode group corresponding to the position of the adjacent light receiving element, the isolation means is set in the inoperative state, and at the time of charge transfer, the isolation By operating the unit, the solid-state imaging device, wherein said commonly connected plurality of sets of accumulated charge collected at different positions for each of the electrode group was prevented causing turbidity from each other. 4. The isolation means is configured as a channel stop region at the boundary between electrode groups adjacent to each other along the charge transfer direction, and the impurity concentration of the channel stop region is
During signal charge storage, the potential for signal charge in the channel stop region becomes equal to or lower than the potential of the light receiving element other than the charge storage unit, so that the channel stop function of the channel stop region becomes inoperative. At the time of charge transfer, the potential for the signal charge in the channel stop region becomes higher than the potential of the light receiving element located corresponding to the electrode group to which the transfer pulse is applied among the plurality of electrode groups, and the channel stop in the channel stop region The solid-state imaging device according to claim 3, wherein the function is set so as to be in an operating state. 5. The isolation means is configured as a channel stop region using a channel stop electrode at a boundary between electrode groups adjacent to each other along a charge transfer direction, and a potential for signal charge in the channel stop region is applied to the channel stop electrode. The solid-state imaging device according to claim 3, wherein the channel stop function is controlled by applying a predetermined voltage. 6. The solid-state image pickup device according to claim 3, wherein a directional transfer electrode is used as the isolation means.