JPH0324873A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To increase the amount of electric charges to be handled by providing plural electric charge accumulation parts which accumulate the electric charge of a second electric charge transfer part transiently corresponding to a light receiving part, and adding the electri charges of plural number of times at the electric charge accumulation parts. CONSTITUTION:The electric charge accumulation part 5 is provided at the side part of the second electric charge transfer part 4, and the electric charge accumulation part 5 is provided between the second electric charge transfer parts 4 on every row, and arranged corresponding to the number of picture elements of the light receiving part 2. Signal electric charges of plural number of times can be accumulated in the electric charge accumulation part 5. The bidirectional transfer of the electric charge is performed between the electric charge accumulation part 5 and the second electric charge transfer part 4. Also, a transfer control gate can be provided between the electric charge accumulation part 5 and the second electric charge transfer part 4 to control the bidirectional transfer of the electric charge. In such a manner, it is possible to increase the amount of electric charges to be handled, and to realize high resolution and high sensitivity simultaneously.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a solid-state imaging device in which a signal charge generated in a light receiving part is transferred by a charge transfer part, and in particular, the amount of charge handled is improved. [Summary of the Invention] A first invention of the present application provides a solid-state imaging device that transfers charges from a plurality of light receiving sections through first and second charge transfer sections, each of which has a second charge transfer section corresponding to the light receiving section. By providing a plurality of charge storage sections that temporarily store the charge of the charge transfer section, and adding the charges of multiple times in the charge storage section,
This increases the amount of charge handled. Further, a second invention of the present application is a solid-state imaging device in which transfer from a light receiving section to a charge transfer section is controlled by a readout gate, in which the readout gate is set in a transfer state during a charge accumulation period to transfer charges to the charge transfer section. During the charge transfer period, the readout gate is cut off, thereby increasing the amount of charge handled. [
[Background Art] Solid-state imaging devices used in video cameras, image readers, etc. and outputting image signals are becoming increasingly high-resolution along with advances in semiconductor microfabrication technology. Incidentally, a solid-state imaging device, particularly a CCD imager, has a light-receiving section made of a photodiode on a semiconductor substrate, and signal charges photoelectrically converted in the light-receiving section are transferred by a charge transfer section. These light receiving parts and charge transfer parts are arranged two-dimensionally on the surface of the substrate. [Problems to be solved by the invention] In order to increase the resolution of solid-state imaging devices, each light receiving section, charge transfer section, etc. are miniaturized. As a result, the area of each light-receiving section and the area of the charge transfer section are reduced, and the amount of charge handled per unit cell is reduced. When handling charges are added in this way, a problem arises in that the dynamic range is insufficient and the S/N ratio deteriorates. Therefore, in view of the above-mentioned technical problems, the present invention aims to provide a solid-state imaging device that increases the amount of charge handled and simultaneously achieves high resolution and high sensitivity. [Means for Solving the Problems] A solid-state imaging device of the first invention of the present application for achieving the above-mentioned object includes a plurality of light receiving sections and a first charge transfer device that transfers charges from the light receiving sections. a second charge transfer section that transfers charges from the first charge transfer section; and a second charge transfer section that is provided on a side of the second charge transfer section and corresponds to the light receiving section. The present invention is characterized in that it has a plurality of charge accumulation sections that temporarily accumulate charges of the light receiving section, and the charge accumulation sections add up the charges transferred from the light receiving section a plurality of times.

Here, the light receiving sections are arranged, for example, in a matrix or in a line. When the light receiving parts are arranged in a matrix, the first charge transfer parts can be formed along the vertical rows of the light receiving parts, and the transfer direction of the second charge transfer parts can also be in the vertical direction. In this case, a horizontal charge transfer section may be provided at the end of the second charge transfer section, or a horizontal charge transfer section may be provided via an accumulation register section. It is preferable that the capacitance of the charge storage section is larger than the capacitance of the light receiving section and the charge transfer section. The above-mentioned multiple times is 2 or more times, and is not limited. Further, the solid-state imaging device of the second invention of the present application includes a plurality of light receiving sections as described above, a charge transfer section that transfers charges from the light receiving sections, and a structure between the charge transfer section and the light receiving section. It has a readout gate. In the case where the light receiving sections are arranged in a matrix, a horizontal charge transfer section, a second charge transfer section for temporary storage, etc. can be provided. And, the present invention has a charge of 141
The present invention is characterized in that during one period, the readout gate is placed in a transfer state to transfer charges to the charge transfer section, and during the charge transfer period, the readout gate is placed in a cutoff state.

[Effect]

In the solid-state imaging device of the first invention of the present application, the amount of charge doubled according to the plurality of times is accumulated in the charge storage section provided on the side of the second charge transfer section, and and second
without increasing the amount of charge handled by the charge transfer section.
The amount of charge handled can be increased by time-sharing the charge transfer. Furthermore, in the solid-state imaging device of the second aspect of the invention, the readout gate is placed in the transfer state during the charge accumulation period, and the signal charges generated in the light receiving section also flow into the charge transfer section. Therefore, signal charges are accumulated not only in the light receiving section but also in the charge transfer section, increasing the amount of charge handled and increasing sensitivity. Furthermore, by keeping the readout gate in a cut-off state during the charge transfer period, it is possible to prevent charges from being mixed with other light receiving sections. [Example] A preferred example of the present invention will be described with reference to the drawings. First Embodiment The solid-state imaging device of this embodiment is an example of a CCD imager that transfers charge a plurality of times to a second charge transfer section.

Figure 1 shows its structure. This CCD imager 1 is
It is shaped by microfabrication of a semiconductor substrate, and the first
As shown in the figure, a plurality of light receiving sections 2 are arranged in a matrix at predetermined intervals.

The light receiving section 2 has a photodiode and generates a signal charge according to the incident light. A first charge transfer section 3 is formed for each column along the vertical columns of the light receiving sections 2. This light receiving section 2
The relationship between the charge transfer section 3 and the first charge transfer section 3 is the same as that of a normal interline transfer type CCD image. In the first charge transfer section 3, a required transfer electrode group is formed, and charge transfer is performed by supplying a multiphase transfer clock (IMΦ) to the transfer electrode group. Although not shown, a readout gate may be provided between the light receiving section 2 and the first charge transfer section 3, and the readout gate allows the light receiving section 2 and the first charge transfer section 3 to be It is possible to control the transfer, or readout, of the charge between the two. A second charge transfer section 4 is formed at each end of the first charge transfer section 3 in the transfer direction in each column.

The second charge transfer unit 4 is electrically connected to the first charge transfer unit 3, and similarly, a required transfer electrode group is released, and a multiphase transfer clock (STΦ) is applied to the transfer electrode group. This causes charge transfer. A charge storage section 5 is formed on the side of these second charge transfer sections 4. The charge storage sections 5 are provided between the second charge transfer sections 4 in each column, and are arranged in accordance with the number of pixels of the light receiving section 2. This charge storage section 5
The signal charges for multiple times are added up. This charge storage section 5
Charge transfer is performed bidirectionally between the charge transfer section 4 and the second charge transfer section 4. A transfer control gate can be provided between the charge storage section 5 and the second charge transfer section 4 in order to control charge transfer in both directions. A horizontal charge transfer section 6 is further provided at each end and electrically connected to each end. This horizontal charge transfer section 6 is for transferring the signal charges of the second charge transfer section 4 of each column for each horizontal line. Charges are also transferred to this horizontal charge transfer section 6 by a transfer electrode to which a required transfer clock is supplied.

At the terminal end of the horizontal charge transfer section 6, an output buffer 7 for converting charge into voltage and outputting it is formed, and a video signal is output from this output buffer 7. In addition,
A light-shielding film made of an aluminum film or the like is formed in each region other than the light-receiving section 2. The CCD imager of this embodiment having such a structure transfers charges to the charge storage section 5 multiple times within the vertical blanking period of the video signal. The second example of this operation is
This will be explained with reference to the figure. First, as shown in FIG. 2, the signal V mLK falls and the vertical blanking period T
Assume that 8LK has started. Then, during the vertical planking period T ltx, there are periodically three reading pulses Φllol+ΦR. ! Φ、. , is supplied to the transfer electrode of the first charge transfer section 3. This each read pulse Φ,. 1
, Φ5.2, Φ7. , from the light receiving section 2 to the first
Transfer of charges to the charge transfer unit 3 is performed. At the time of these transfers, the accumulated signal charges are divided into three parts and read out using a period other than the vertical blanking period as an accumulation period, so that, for example, each read pulse Φ. ,,Φ,. 2. The level of ΦRO2 can be adjusted by tJ4 to adjust the charge handled for one time, and the level of the readout gate can be adjusted to adjust the height of the potential barrier of the readout gate. Since the amount of charge can be transferred in three steps in this manner, the amount of charge handled by the first charge transfer section 3 can be reduced to one-third of the amount of charge that is transferred at one time. Each read pulse Φa. 1. Φ8.2, Φ8. Immediately after the timing of , the signal charge is present in the first charge transfer section 3. . Therefore, as shown in the signal IMΦ and the signal STΦ, the signals supplied to each transfer electrode of the first and second charge transfer sections 3.4 are made to be in the transfer clonk signal state, and each period T
．． Then, the signal charge is transferred to the second charge transfer section 4 by the first charge transfer section 3 and the second charge transfer section 4 working together.
Then, the signal charges transferred to the second charge transfer unit 4 are transferred to the charge storage unit 5 provided on the side of the second charge transfer unit 4 at the timing of time M in the figure, and the charges are transferred to the charge storage unit 5 provided on the side of the second charge transfer unit 4. The data are temporarily stored in the storage unit 5 and added. In addition,
It is not necessary to store charges in the charge storage section 5 at the final time M during the period TILK. After the accumulation operation in the charge storage section 5 is performed three times, reading from the charge storage section 5 to the second charge transfer section 4 is performed again at the timing of the pulse ΦP. Then, the vertical blanking period TILK ends, and during the video period, signal charges are sent from the second charge transfer section 4 to the horizontal charge transfer section 6 by the line shift pulse Φ1. The charges transferred to the horizontal charge transfer section 6 are transferred within the horizontal charge transfer section 6 during the period between the line shift pulses Φts, and a required video signal is finally taken out from the output buffer 7. In the above embodiment, the number of times charge is transferred from the light receiving section 2 to the first charge transfer section 3 within the vertical blanking period is set to 3.
However, it is not limited to this. Second Embodiment The solid-state imaging device of this embodiment is a CCD imager having a structure in which a third charge transfer section is provided between the second charge transfer section and the horizontal charge transfer section of the first embodiment. This is an example. Its structure is shown in Figure 3. Similar to the first embodiment, this CCD image +11 is formed by finely processing a semiconductor substrate, and a plurality of light receiving parts 12 arranged in a matrix at predetermined intervals are formed. The light receiving section 12 has a photodiode and generates a signal charge according to incident light. A first charge transfer section 13 is formed in each column along the vertical rows of the light receiving sections 12. In the first charge transfer section l3, a required transfer electrode group is formed, and charge transfer is performed by supplying a multiphase transfer clock (IMΦ) to the transfer electrode group. Although not shown, a readout gate may be provided between the light receiving section 12 and the first charge transfer section 13. A second charge transfer section l4 is formed at each end of the first charge transfer section l3 in the transfer direction of each column. The second charge transfer unit 14 is electrically connected to the first charge transfer unit 13, has a required transfer electrode group, and applies a multiphase transfer clock (STΦ) to the transfer electrode group. This causes charge transfer. Charge storage portions l5 are formed on the sides of these second charge transfer portions l4. These charge storage parts 15
are provided between the second charge transfer sections 14 in each column, and are arranged in accordance with the number of pixels of the light receiving section l2. These charge storage units 15 add charges for multiple times. Charge is transferred bidirectionally between the charge storage section 15 and the second charge transfer section l4. Charge storage section I5 and second charge transfer section 1
A structure may also be provided in which a transfer control gate is provided to control the transfer of charges between the two. At the end of the second charge transfer section l4 in the transfer direction, there is a third charge transfer section l4.
A charge transfer section l8 is implemented. This third charge transfer section 18 is electrically connected to the second charge transfer section 14, similarly has a required transfer electrode group formed therein, and applies a multiphase transfer cross (ST2Φ) to the transfer electrode group. This causes charge transfer.

This third charge transfer section 1 is connected to the next horizontal charge transfer section l6.
It is used to wait for the turn of charge transfer to the CCD, and has a function similar to the storage section of a frame interline type CCD.

A horizontal charge transfer section 16 is electrically connected to and provided at the end of the third charge transfer section l8 in the charge transfer direction.

This horizontal charge transfer section 16 is a third charge transfer section 18 in each column.
This is to transfer the signal charge for each horizontal line. Charges are also transferred to this horizontal charge transfer section 16 by a transfer electrode to which a required transfer clock is supplied. At the terminal end of this horizontal charge transfer section 16, there is an output buffer 17 for converting charge into voltage and outputting it. A video signal is output from this output buffer 17. Note that a required light shielding film is formed in the area other than the light receiving portion l2. Next, the operation of this CCD imager will be explained with reference to FIG. In the CCD imager of this embodiment, the timing of charge transfer from the light receiving section l2 to the first charge transfer section l3 can be performed even during a period other than the vertical blanking period.

First, as shown in FIG. 4, the vertical planking period TI
After completion of LE, the read pulse Φ,■ is supplied to the transfer electrode of the first charge transfer unit 13 as the signal IMΦ supplied to the first charge transfer unit 13. This read pulse Φ
2), charges are read out from the light receiving section l2 to the first charge transfer section 13. After the read operation to the first charge transfer section 13, a transfer clock signal is applied to both the transfer electrodes of the first charge transfer section 13 and the second charge transfer section 14, and the transfer clock signal is applied to the transfer electrodes of the first charge transfer section 13 and the second charge transfer section 14, and the period T. During this period, charges are transferred from the first charge transfer section 13 to the second charge transfer section 14. After the transfer to the second charge transfer section 14, at the timing M in the figure, an operation of accumulating charges from the second charge transfer section 14 to the charge storage section l5 is performed. In the CCD imager of this embodiment, such a transfer operation from the light receiving section 12 to the charge storage section 15 via the first and second charge transfer sections 13 and 14 is repeatedly performed n times during the image period. That is, by repeating the transfer n times, charges for n times are added in the charge storage section 15. As a result, the amount of charge to be handled will be increased by n times, and a large amount of charge to be handled will be obtained. Furthermore, due to the function of the third charge transfer section 18, which will be explained next, in the readout of this embodiment, it is not necessary to transfer from the light receiving section 12 only during the vertical blanking period, so that the image period can be evenly divided. , the amount of charge handled can be increased. In the COD imager of this embodiment, the storage period of the light receiving section 12 can be made equal to the readout timing, and there is no need to adjust the readout gate or pulse level. After the transfer from the light receiving section 12 to the charge storage section 15 is repeated n times, a read pulse ΦP is applied to the signal STΦ. Then, the charges added to the charge storage section l5 n times are returned to the second charge storage section 14 all at once.
After applying the pulse ΦP, the vertical planking period T
During the period T2 during ILX, the second charge transfer unit l4 to the third
The charge is transferred to the charge transfer unit 15. As a result, all the signal charges for one field have been moved to the third charge transfer section l8, and during the next video period, they are transferred again to n in the first and second charge transfer sections 13.14.
Transfer of charge is possible.

The charges transferred to the third charge transfer unit 15 in this way are sent to the horizontal charge transfer unit l6 for each horizontal line at the timing of the line shift pulse Φ, during the next video period, and During the period between the shift pulses ΦL, the charges are transferred through the horizontal charge transfer unit l6, and are finally transferred to the output buffer 1.
The required video signal is taken out from 7.

Such a third charge transfer section l8 is called a horizontal charge transfer section l6.
and the second charge transfer section 14.
In the imager, charge is transferred n times during the 1-field period, rather than having multiple charge transfers performed only during the vertical blanking period. Therefore, even if it is difficult to transfer data multiple times within a short period of time due to wiring delays, etc., sufficient reading is possible. Then, by reading the data n times, the amount of charge to be handled is increased by n times, and the dynamic range and S/N ratio can be improved.

Third Embodiment This embodiment is an example of a CCD imager in which the readout gate is placed in a transfer state during the charge accumulation period in the light receiving section, and the charge transfer section is used for charge accumulation. First, its structure is that of a normal frame interline transfer type CCD, as shown in FIG. That is, the CCD imager 3l is formed by finely processing a semiconductor substrate, and has a plurality of light receiving sections 32 arranged in a matrix at predetermined intervals. Generates signal charges in response to light. Along the vertical rows of these light receiving sections 32, the first
A charge transfer unit 33 is implemented. A channel stopper area is formed around each light receiving section 32, and each light receiving section 32 is provided with a channel stopper area.
A read gate is provided between the charge transfer section 33 and the first charge transfer section 33. This readout gate has a structure using a part of the transfer electrode, and when the highest voltage is applied to the transfer electrode driven at a ternary level, the potential barrier at the readout gate portion becomes low, and the light receiving part 32 The charges are read out to the first charge transfer section 33. The charge from the light receiving section 32 is transferred to the first charge transfer section 33 via the readout gate. Note that the structure is not such that a part of the transfer electrode is used as the readout gate, but has an independent readout gate. It can also be a structure. The first charge transfer unit 33 has a required transfer electrode group, and charges are transferred by supplying a multiphase transfer clock (IMΦ) to the transfer electrode group. the first in each of those columns
At the end of the charge transfer section 33 in the transfer direction, a second
A charge transfer unit 34 is implemented. Second charge transfer section 34
is electrically connected to the first charge transfer unit 33, a required transfer electrode group is formed in the same way, and charge transfer is performed by applying a multiphase transfer clock (STΦ) to the transfer electrode group. It will happen. The second charge transfer section 34 includes the first charge transfer section 3
Charge is transferred from the second charge transfer section 34 at high speed, and the charge is temporarily stored in the second charge transfer section 34. A horizontal charge transfer section 36 is further provided at each end of the second charge transfer section 34 in the transfer direction, electrically connected to each end. This horizontal charge transfer section 36 is for transferring the signal charges of the second charge transfer section 34 of each column for each horizontal line. This horizontal charge transfer section 36 also includes
Charges are transferred by the transfer electrodes that are supplied with the required transfer clock. An output buffer 37 is formed at the terminal end of the horizontal charge transfer section 36 for converting charge into voltage and outputting it, and a video signal is output from this output buffer 37. Note that a light-shielding film made of an aluminum film or the like is formed in each region other than the light-receiving portion 32. The CCD imager of this embodiment having the structure described above operates as follows. First, during the charge transfer period, the read gate is cut off. That is, the state of the potential near the light receiving section 32 is the readout gate potential Φ, as shown in FIG. . Barriers to this will be raised. The charges accumulated in the potential well Φ of the first charge transfer section 33 are transferred in accordance with the multiphase transfer clock, but during this time the potential well Φ of the read gate. . . The barrier remains high, and charges from other photodetectors do not mix. This charge transfer is from the first charge transfer section 33 to the second charge transfer section 34, and is carried out during the vertical blanking period, similar to a normal frame interline transfer type CCD imager. It is. Next, during the charge accumulation period, what about the readout gate? It is considered to be in a sending state. That is, the state of the potential near the light receiving section 32 is as shown in FIG. 7, as shown in FIG. . . is approximately the same value as the potential Φ gate of the light receiving section 32. Furthermore, the potential well Φ of the first charge transfer section 33 is also made deeper. Such a transfer state occurs when a high voltage is applied to the transfer electrode. This is possible by supplying a signal. From this potential distribution, the charges generated in the light receiving section 32 are accumulated in the light receiving section 32 and also in the first charge transfer section 33. This essentially means that the storage capacity has increased, meaning that the amount of charge to be handled increases. The readout gate potential Φ■ during such charge accumulation period. The action of lowering 6 is
A high D is applied to the transfer electrode across the readout gate during the storage period.
This may be done by applying a C voltage, or by periodically supplying a pulse that lowers the potential ΦIIOG of the readout gate during the period when the light receiving section 32 is performing accumulation. Note that charge transfer from the second charge transfer unit 34 to the horizontal charge transfer unit 36 is performed for each horizontal line during the video period.

As described above, in the CCD image of this embodiment, signal charges are accumulated not only in the light receiving section 32 but also in the first charge transfer section 33 during the accumulation period, so that the amount of handled charges increases. As a result, the dynamic range and S/N ratio will be improved.

〔Effect of the invention〕

The solid-state imaging device of the present invention has a structure in which charges are transferred multiple times to the charge accumulation section on the side of the second charge transfer section, and a readout gate between the light receiving section and the charge transfer section is placed in a transfer state during the charge accumulation period. By keeping it as such, the amount of charge it can handle can be increased. Therefore, it is possible to achieve higher sensitivity, an improvement in the dynamic range, and an improvement in the S/N ratio.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the planar structure of an example of the solid-state imaging device of the present invention, FIG. 2 is a timing chart for explaining the operation of the example, and FIG. 3 is another example of the solid-state imaging device of the invention. FIG. 4 is a timing chart for explaining the operation of the other example described above. Further, FIG. 5 is a schematic diagram showing the planar structure of still another example of the solid-state imaging device of the present invention, and FIG. 6 is a potential distribution showing the state of the potential near the light receiving part during transfer of the above-mentioned still another example. 7 are potential distribution diagrams showing the state of the potential near the light-receiving section during accumulation in still another example of the above. 1.11.31...CCD imager 2, 12.32
... Light receiving section 3, 13.33... First charge transfer section 4.14.14
...Second charge transfer section 5, 15...Charge storage section 6, 16.36...Horizontal charge transfer section 7, 17.37...Output buffer

Claims (2)

[Claims] (1) A plurality of light receiving sections, a first charge transfer section that transfers charges from the light receiving sections, a second charge transfer section that transfers charges from the first charge transfer section, and a second charge transfer section that transfers charges from the first charge transfer section; A plurality of charge storage sections are provided on the sides of the charge transfer section and temporarily accumulate the charges of the second charge transfer section corresponding to the light reception section, and the charge storage section temporarily stores the charges of the second charge transfer section, which are transferred from the light reception section a plurality of times. A solid-state imaging device characterized in that the charges of are added in the charge storage section. (2) It has a plurality of light receiving sections, a charge transfer section that transfers charges from the light receiving sections, and a readout gate formed between the charge transfer section and the light receiving section, and during the charge accumulation period, A solid-state imaging device, characterized in that the readout gate is placed in a transfer state to accumulate charge in the charge transfer section, and the readout gate is placed in a cutoff state during a charge transfer period.