JPH1127476A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pickup device that has an over flow control function even in the case that a sensor section has a potential step difference decreasing in its read-out direction. SOLUTION: In a CCD linear sensor having a sensor structure longer in its read-out direction and having a potential gradient decreasing in the read direction, a potential barrier to determine a charge amount processed by each memory section 13c is formed in the vicinity of each memory section 13c in a plurality of vertical transmission paths 13 through which signal charges of each sensor section 11 are transferred, and an overflow control gate electrode 19 is provided on an upper part of the potential barrier. Signal charges exceeding the potential barrier under the overflow control gate electrode 19 are swept out to a drain section 17b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device, and more particularly to a solid-state imaging device having a so-called horizontal overflow drain structure in which a charge discharging portion is formed in a lateral direction of a sensor section (photoelectric conversion element).

[0002]

2. Description of the Related Art As an example of this type of solid-state imaging device, C
FIG. 4 shows a CD (Charge Coupled Device) linear sensor. In the figure, on one side of a sensor array 102 in which a large number of sensor units 101 are linearly arranged, signal charges read from each sensor unit 101 via a read gate unit 103 are arranged in the direction in which the sensor arrays 102 are arranged. Is provided, and on the opposite side, an overflow drain structure including a charge discharging gate 105 and a charge discharging unit 106 is provided. The signal charge transferred by the charge transfer unit 104 is converted into a voltage by the charge-voltage conversion unit 107, and is output via the buffer 108 to the output terminal 10.
9 to a signal processing system (not shown). FIG.
3 shows a potential distribution in the XY section of FIG.

In the conventional CCD linear sensor having the above-described configuration, the photoelectric conversion in the sensor 101
When the amount of electric charge stored in 01 exceeds the potential barrier of the charge discharging gate unit 105, the excess signal charge is discharged to the charge discharging drain unit 106 via the charge discharging gate unit 105.

At the time of reading signal charges, a read gate pulse φROG is applied to the read gate electrode 111 of the read gate section 103, and the potential under the read gate electrode 111 is changed from a shallow state to a deep state, whereby each sensor is read. The signal charges stored in the unit 101 are read. Then, by applying, for example, two-phase shift pulses φH1 and φH2 to the transfer gate electrodes 112 arranged in the transfer direction of the charge transfer unit 104, the signal charges are read out from below the readout gate electrode 111 and transferred.

[0005]

By the way, bar code reading sensors and camera AF (Automatic Focussing)
In CCD linear sensors used as sensors, etc.,
For the purpose of improving the sensitivity and the like, a sensor structure that is long in a signal charge reading direction is employed. When a CCD linear sensor having such a sensor structure is provided with the horizontal overflow drain structure as described above, a read afterimage due to a read failure due to the sensor length becomes a problem. This problem can be alleviated by setting a longer signal charge read time, but this limits the specification conditions of the linear sensor.

As a countermeasure for the structure of the sensor unit 101, a potential step is provided in the sensor unit 101 in the signal charge reading direction as shown in the potential diagram of FIG. A method is conceivable in which a signal charge is easily read by providing a step-like potential gradient that goes down in the read direction, and read afterimage caused by the sensor length is suppressed.

However, when this method is employed, it is possible to eliminate the reading failure of the signal charges from the sensor unit 101, but due to the potential step in the sensor unit 101, the charge transfer unit 10
In the case of the horizontal overflow drain structure in which the charge discharge drain portion 106 is disposed on the side opposite to the above, it is difficult to control the overflow barrier potential, and there is a problem that the overflow control function cannot be provided.

The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an overflow control function even when a potential step is formed in a sensor section in a reading direction. An object of the present invention is to provide a solid-state imaging device that can be provided.

[0009]

According to the present invention, there is provided a solid-state imaging device comprising: a sensor array in which a plurality of sensor units are arrayed; a charge transfer unit for transferring signal charges in an array direction of the sensor arrays; A plurality of transfer paths for transferring the signal charges photoelectrically converted by each sensor section to the charge transfer section for each sensor section, and handling of the transfer sections provided near the transfer section in the middle of the plurality of transfer paths. And a charge discharging unit for discharging signal charges exceeding the charge amount.

In the solid-state imaging device having the above-described configuration, the plurality of transfer paths transfer the signal charges photoelectrically converted by each sensor unit of the sensor array to the charge transfer unit for each sensor unit. At this time, if the amount of signal charge transferred here exceeds the amount of charge handled by the transfer unit in the transfer unit in the middle of the plurality of transfer paths, the excess signal charge is swept by the charge discharge unit. Discarded. As a result, overflow of signal charges is eliminated, and problems such as mixing of signal charges of adjacent pixels are eliminated.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic plan view showing an embodiment of the present invention applied to a CCD linear sensor used as an AF sensor or the like. In addition,
The CCD linear sensor according to this embodiment adopts a configuration in which a large number of linearly arranged sensor units are divided into a plurality of blocks in the arrangement direction, and the accumulation time of signal charges can be arbitrarily set for each block. And

In FIG. 1, a large number of sensor units 11 are linearly arranged to form a sensor array 12. Sensor part 1
1 comprises a photoelectric conversion element such as a photodiode,
The light incident on the light receiving surface is converted into a signal charge having a charge amount corresponding to the light amount and stored. The sensor unit 11 has a sensor structure that is long in a signal charge readout direction (up and down direction in the figure) for the purpose of improving sensitivity and the like. In addition, in order to suppress read-out afterimages caused by the sensor length, the sensor unit 1
1, a potential difference is provided in the signal charge readout direction, and a sensor structure is provided in the sensor unit 11 with a step-like potential gradient falling in the readout direction (see FIG. 6).

On one side of the sensor array 12, a sensor section 11 is provided.
The vertical transfer path 13 extending in the longitudinal direction of the
Each is formed. A first read gate electrode 14 is provided between the sensor array 12 and each vertical transfer path 13. When a first read gate pulse φROG1 is applied to the first read gate electrode 14, each sensor is The signal charges stored in the section 11 are read out to the respective vertical transfer paths 13 under the first readout gate electrode 14.

Although FIG. 1 shows the first readout gate electrode 14 as one continuous electrode, the CCD linear sensor according to the present embodiment has a large number of sensor units 11 arranged. In order to divide the signal charge from the sensor unit 11 for each block, it is necessary to divide the signal charge from the sensor unit 11 for each block. The first read gate electrode 14 is also formed independently for each block, and a read gate pulse is applied at a different timing for each gate electrode.

The vertical transfer path 13 includes a first buffer section 13a which receives a signal charge read from the sensor section 11, and a second buffer section 13b which is continuous with the first buffer section 13a.
And a memory unit 1 that is continuous with the second buffer 13b and temporarily holds signal charges read from the sensor unit 11.
3c. In this vertical transfer path 13, the first and second buffer sections 13 a and 13 b
A transfer gate electrode 15 is provided, and the second buffer unit 13b
The second transfer gate electrode 16 is provided between the first transfer gate electrode 16 and the memory unit 13c.

When the first transfer gate pulse φV1 is applied to the first transfer gate electrode 15, the sensor unit 1
The signal charges read from 1 to the first buffer unit 13a are transferred to the second buffer unit 13b. Further, when the second transfer gate pulse φV2 is applied to the second transfer gate electrode 16, the second buffer unit 1
The signal charges transferred to 3b are further transferred to the memory unit 13c.

The memory unit 13c divides a large number of sensor units 11 into a plurality of blocks in the arrangement direction, and changes the accumulation time of signal charges for each block. Since the signal charges of the unit 11 are read first, the previously read signal charges are held for a period until the signal charges of the sensor units 11 in the block having the longest accumulation time are read. It is provided in.

A drain portion 17 for discharging signal charges is formed in a region between the first buffer portions 13a of each vertical transfer path 13, for example, on an extension of a boundary between the sensor portions 11. I have. And these drain portions 17
Out of every other drain portion 17a and the first
A shutter gate electrode 18 is provided between the buffer portions 13a.
Is provided.

By applying the shutter gate pulse φSG to the shutter gate electrode 18, all the signal charges read out to the first buffer section 13 a of each vertical transfer path 13 pass under the shutter gate electrode 18 and each drain section 17 a Is discharged. That is, when the first readout gate pulse φROG1 is applied to the first readout gate electrode 14 and the shutter gate pulse φSG is applied to the shutter gate electrode 18 at the same time, the signal charges of the sensor units 11 are simultaneously transmitted to the drain unit 17a. An electronic shutter that can be swept away can be realized.

In the vertical transfer path 13, an overflow control gate electrode 19 is provided adjacent to the memory section 13c in a region opposite to the region where the shutter gate electrode 18 is provided. The overflow control gate electrode 19 is formed integrally with, for example, the second transfer gate electrode 16. in this case,
The second transfer gate pulse φV2 also has a function as an overflow control gate pulse φOFCG.

The overflow control gate electrode 19 does not necessarily need to have an electrode structure integral with the second transfer gate electrode 16. However, since the potential below the overflow control gate electrode 19 needs to move up and down in synchronization with the potential below the second transfer gate electrode 16 as described later, the potential of the overflow control gate electrode 19 is changed to the second transfer potential. It is more advantageous to form the electrode structure integral with the gate electrode 16 and apply the same gate pulse.

Overflow control gate electrode 1
Potential barrier 22 below 9 (see FIG. 3B)
Is set to a height corresponding to the amount of charge handled by the memory unit 13c. That is, when the amount of signal charge transferred to the memory unit 13c exceeds the amount of charge handled by the memory unit 13c, the amount of the excess charge exceeds the potential barrier 22 below the overflow control gate electrode 19. Has become.

In the region where the overflow control gate electrode 19 is provided, there is a drain portion 17b different from the drain portion 17a. The region where the drain portion 17b exists has a potential gradient that falls from the side of the memory portion 13c toward the drain portion 17b. Due to the action of this potential gradient, the charges that have passed through the potential barrier 22 below the overflow control gate electrode 19 move between the vertical transfer paths 13 and are discharged to the drain portion 17b (horizontal type). Overflow drain structure).

A horizontal charge transfer section 20 is provided adjacent to the vertical transfer path 13 on the side opposite to the sensor array 12. In addition, a second read gate electrode 21 is provided between each memory unit 13 c and the horizontal charge transfer unit 20 in the vertical transfer path 13. By applying the second readout gate pulse φROG2 to the second readout gate electrode 21, the signal charges accumulated in each memory unit 13c are read out to the horizontal charge transfer unit 20 at the same time.

The horizontal charge transfer section 20 has, for example, a two-layer electrode structure, and is driven in two phases by horizontal transfer pulses φH1 and φH2 to thereby transfer signal charges transferred from each memory section 13c of the vertical transfer path 13. Are sequentially transferred horizontally.
The horizontally transferred signal charge is converted into a voltage by a charge-voltage converter (not shown) and output.

Next, the CCD according to the present embodiment having the above configuration will be described.
In the linear sensor, the first readout gate electrode 14,
First transfer gate electrode 15 and second transfer gate electrode 16
/ Overflow control gate electrode 19
, A first transfer gate pulse φV1, and a second transfer gate pulse φV2.
/ Overflow control gate pulse φOFCG
The operation in the case where is applied will be described below with reference to the potential diagrams of FIGS. 3 (A) and 3 (B).

Here, FIGS. 3A and 3B correspond to X in FIG.
The potential distribution on the -X 'line section and the YY' line section are shown, respectively. In FIG. 1, each of the first readout gate electrode 14, the first transfer gate electrode 15, and the second transfer gate electrode 16 / overflow control gate electrode 19 is schematically shown as having a narrow structure. However, in actuality, as shown in FIGS. 3A and 3B, the electrode structure is wide enough to overlap each other.

In FIG. 2, a period from the fall timing of the first read gate pulse φROG1 to the fall timing of the next pulse is an accumulation period in which photoelectric conversion is performed in the sensor unit 11 and signal charges are accumulated. is there. The signal charge stored in the sensor unit 11 is increased by the rise of the first read gate pulse φROG1 and the potential under the first read gate electrode 14 is deepened.
Is read out.

The read signal charges are read into the first buffer section 13a by the fall of the first read gate pulse φROG1 and the rise of the first and second transfer gate pulses φV1 and φV2 in synchronization with the fall. The output signal charges are transferred to the memory unit 1 via the second buffer unit 13b.
3c. Then, the first transfer gate pulse φV
When 1 falls, the transfer of the signal charge to the memory unit 13c is completed.

In the memory section 13c, as described above, since the second transfer gate electrode 16 is actually a wide electrode, a high-level second transfer gate pulse φV2 is applied to the second transfer gate electrode 16. Is applied, the overall potential of the memory section 13c is deepened. As a result, the potential difference between the memory unit 13c and the potential barrier 22 that determines the amount of electric charge handled increases. That is, this is equivalent to an increase in the potential of the potential barrier 22, and the amount of charge handled by the memory unit 13c becomes larger than the initially set amount.

Therefore, in the present embodiment, the memory unit 13c
The overflow control gate electrode 19 is disposed above the potential barrier 22 that determines the amount of charge to be handled, and the second transfer gate pulse φV2 is also applied to the overflow control gate electrode 19 as the overflow control gate pulse φOFCG. .

As a result, the potential of the potential barrier 22 also moves up and down following the up and down movement of the potential of the memory section 13c. Therefore, the relative potential between the memory section 13c and the potential barrier 22 becomes equal to the second transfer gate pulse φV2. Irrespective of the application / non-application, the voltage is always constant, and the amount of electric charges handled by the memory section 13c is always maintained at the initially set amount by the potential barrier 22.

In the memory section 13c, when the signal charge exceeds the handling charge and overflows, the signal charge corresponding to the overflow exceeds the potential barrier 22 below the overflow control gate electrode 19, and is further transferred vertically. Through the potential gradient 23 (see FIG. 3 (B)) formed in the region between the paths 13, it is swept away by the drain portion 17 b. Thereby, it is possible to suppress the overflow of the signal charges in the memory section 13c.

As described above, the amount of charge handled by the memory unit 13c is located in the vicinity of a transfer unit, for example, the memory unit 13c in the vertical transfer path 13 for transferring the signal charges of each sensor unit 11 to the horizontal charge transfer unit 20. Is formed, and a signal charge exceeding the potential barrier 22 is passed through a potential gradient 23 to form a drain portion 17b.
In the CCD linear sensor that has a long sensor structure in the readout direction and has a potential gradient falling in the readout direction, the overflow control function can be provided, thereby eliminating overflow. Can be.

The overflow drain section 17 is also provided.
By forming b at the same position as the drain portion 17a for the electronic shutter, there is an advantage that a wiring (not shown) for supplying a drain voltage to the drain portions 17a and 17b can be shared. . In addition, since one overflow drain portion 17b is provided for each of the two adjacent sensor portions 11 and 11, space saving can be achieved as compared with the case where one overflow portion is provided for each sensor portion 11. This is a structure that is advantageous for miniaturization.

[0036]

As described above, according to the present invention,
A sensor array in which a plurality of sensor units are arranged, a charge transfer unit that transfers signal charges in an array direction of the sensor arrays, and a plurality of transfers that transfer signal charges photoelectrically converted in each sensor unit to the charge transfer unit A charge discharging section is provided in the vicinity of a transfer section in the middle of a plurality of transfer paths formed on the signal charge readout side, and a signal charge exceeding the charge amount handled by the transfer section is provided in the solid-state imaging device having the transfer path. By discharging, even if the sensor has a long sensor structure in the reading direction and has a potential gradient falling in the reading direction, the overflow control function can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an embodiment of the present invention.

FIG. 2 is a timing chart for explaining an operation according to the embodiment.

FIG. 3 shows a potential distribution (A) in a section taken along line XX ′ in FIG. 1 and a potential distribution (B) in a section taken along line YY ′ in FIG.
FIG.

FIG. 4 is a CCD having a horizontal overflow drain structure.
FIG. 7 is a schematic configuration diagram illustrating a conventional example of a linear sensor.

FIG. 5 is a potential diagram of a cross section taken along line XY of FIG. 4;

FIG. 6 is a potential diagram for explaining a conventional problem.

[Explanation of symbols]

11 sensor part, 12 sensor row, 13 vertical transfer path,
13c: memory unit, 14: first read gate electrode, 1
5 ... first transfer gate electrode, 16 ... second transfer gate electrode,
17a: drain portion for electronic shutter, 17b: drain portion for overflow, 18: gate electrode for electronic shutter, 19: overflow control gate electrode, 2
0: horizontal charge transfer section, 21: second readout gate electrode

Claims (5)

[Claims] 1. A sensor array in which a plurality of sensor units are arranged; a charge transfer unit that transfers signal charges in an array direction of the sensor arrays; and a signal charge photoelectrically converted by each sensor unit in the sensor array. A plurality of transfer paths for transferring to the charge transfer section for each sensor section; and a charge provided near the transfer section in the middle of the plurality of transfer paths to discharge a signal charge exceeding a charge amount handled by the transfer section. A solid-state imaging device comprising a discharge unit. 2. The sensor unit according to claim 1, wherein the sensor unit has a sensor structure that is long in a readout direction and has a potential gradient that decreases in the readout direction.
The solid-state imaging device according to claim 1. 3. The transfer unit in the middle of the plurality of transfer paths,
The solid-state imaging device according to claim 1, wherein the solid-state imaging device is a memory unit that temporarily stores signal charges read from the sensor unit. 4. The charge discharging unit includes a drain unit provided in a region between the plurality of transfer paths, a potential barrier formed adjacent to the memory unit, and a signal transferred to the memory unit. 4. The solid-state imaging device according to claim 3, further comprising: a potential gradient that guides a signal charge that exceeds the potential barrier among the charges to the drain portion. 5. The solid-state imaging device according to claim 4, wherein one drain portion is provided for two adjacent light receiving portions of the sensor row.