JP2508611B2 - Driving method for solid-state imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a solid-state image pickup device, and is particularly suitable for use in an interline type solid-state image pickup device.

[0002]

2. Description of the Related Art An interline CCD solid-state image pickup device has a plurality of light receiving portions 1 which are picture elements arranged at a predetermined pitch in the horizontal and vertical directions, as shown in the principle configuration diagram of FIG.
And C extending in the vertical direction provided on one side of the light receiving unit 1 in each row
A vertical transfer register 2 having a CD structure and a horizontal transfer register 3 having a CCD structure provided at one end of each vertical transfer register 2 are provided, and each light receiving portion 1 corresponds to a signal charge generated according to the amount of light received. It is configured to transfer to the vertical transfer register 2, transfer the signal charge of each vertical transfer register 2 to the horizontal transfer register 3, and read the signal charge for each horizontal line.

Specifically, in a portion corresponding to one pixel (unit cell), as shown in FIG. 5, a read gate portion 4 is arranged between the light receiving portion 1 and the vertical transfer register 2, and other portions of the light receiving portion 1 are provided. An overflow drain 6 is provided on the side through an overflow control gate unit 5. Each pixel is divided in the channel stop area 7.

FIG. 4A is a potential diagram of a light receiving state, in which charges 8 corresponding to the amount of light received are accumulated in the light receiving unit 1, and at the time of reading, as shown in the potential diagram of FIG. The charge 8 of 1 is transferred to the vertical transfer register 2.

In such a solid-state image pickup device, there is proposed a solid-state image pickup device having a horizontal overflow drain structure in which an overflow drain portion for discharging charges of the vertical transfer register 2 is further provided adjacent to the longitudinal side of the vertical transfer register 2. (See, for example, JP-A-63-20976).

[0006]

However, in the above-mentioned solid-state image pickup device, since the horizontal overflow drain portions are provided in the light receiving portion 1 and the vertical transfer register 2, respectively, there is a problem that the area of the element increases. .

If both the overflow drains are of vertical type, the area of the device is reduced. However, such a structure reduces the degree of freedom in designing the density profile under the vertical transfer register and the electronic shutter operation. It may become difficult or the smear characteristics may not be maintained.

The present invention has been made in view of the above problems. An object of the present invention is to eliminate the need for providing charge discharging means in the transfer register, and to reduce the area of the element. In the case of adopting the vertical overflow drain structure, it is not necessary to provide a charge discharging unit in the lower part of the transfer register, and a solid-state imaging device capable of ensuring the degree of freedom in designing the impurity concentration of the semiconductor region under the transfer register and its profile. It is to provide a driving method.

[0009]

DISCLOSURE OF THE INVENTION The present invention is directed to a storage unit that stores an amount of electric charge according to the amount of incident light, and a charge discharge unit that is provided adjacent to the storage unit and discharges the electric charge of the storage unit. In the method for driving a solid-state image pickup device, comprising: means and a transfer register for transferring the charge accumulated in the accumulating unit, the charge in the transfer register is discharged by the charge discharging unit via the accumulating unit. And

In this case, the charge discharging means may have a vertical overflow drain structure.

[0011]

In the driving method of the solid-state image pickup device according to the present invention, since the charge of the transfer register is discharged by the charge discharging means via the accumulating portion, it is not necessary to separately provide the charge discharging means in the transfer register.

[0012]

Embodiments of the interline CCD solid-state image pickup device according to the present invention will be described below with reference to the drawings. In this example, a solid-state image sensor having a horizontal overflow drain structure will be described, but the basic idea is the same even for a solid-state image sensor having a vertical overflow drain structure.

1A to 1D show an embodiment of the operation of the solid-state image pickup device of the present invention, in which the charge 8 according to the amount of light received accumulated in the light receiving portion 1 is vertically passed through the read gate portion 4. After being transferred to the transfer register 2 (A and B in the same figure), the electric charge 8 is measured in the vertical transfer register 2 (C in the same figure).

The residual electric charge 8'generated by this measurement is once returned to the light receiving portion 1, and then the residual electric charge 8'is discarded to the overflow drain 6 through the overflow control gate portion 5 (D in the same figure). The amount of charge measured in this example is: Q _M = Cv × (φv−φ _ROG ). However, Cv is the storage capacity of the vertical transfer register,
(Φv-φ _ROG) is a potential barrier difference of the vertical transfer register 2 and the read gate portion 4.

Here, letting ΔQv be the variation of the accumulated charge amount of the vertical transfer register 2 and δQ be the amount of charge directly flowing into the vertical transfer register 2 at the time of reading, the variation factor of the amount of charge measured in this embodiment will be described. Considering this, the dynamic range is Cv × (φv −φ _ROG ) ＋ △ Cv × (φv −φ _ROG ) ＋ Cv ×
Is set to △ (φv -φ _ROG). Considering the last two terms, ΔCv × (φv −φ _ROG ) of the second term is equal to or less than ΔQv, and Cv × Δ (φv −φ _ROG ) of the third term is Cv < C
Δ (since Cs is the storage capacity of the light receiving unit 1)
It becomes Qs or less.

Therefore, even if the variation component is underestimated, it is reduced by ΔQs + δQ.

Therefore, in this embodiment, the dynamic range is not determined by the structure of the light receiving section 1, and the degree of freedom for the structure of the light receiving section 1 is increased. That is, in the area of the vertical transfer register 2, there is no margin component due to the variation in the accumulated charge amount of the light receiving portion 1, and as a result, the light receiving portion 1
The area can be increased and the sensitivity can be improved.

Next, referring to FIG. 2, the overflow control gate unit 5 is provided with the remaining charge 8'which has once been returned to the light receiving unit 1.
6 shows a potential relationship for realizing a method of discarding the overflow drain 6 via the. In the figure, the solid line (I) is the potential of the light receiving portion 1, and the broken line (II).
Is the potential of the overflow control gate section 5.

Overflow control gate section 5
Has a buried MOS structure, and when the sensor electrode of the light receiving part 1 and the electrode of the overflow control gate part 5 are common, the surface potential of the overflow control gate part 5 is pinned at a certain point to The vertical relationship is reversed.

Therefore, by setting V ₁ to the potential applied to the sensor electrode during light reception and V ₂ to the potential applied to the sensor electrode during transfer of the remaining charge, the remaining charge 8'returned to the light receiving portion 1 is set. The light can be transferred from the light receiving unit 1 to the overflow drain 6.

Usually, in the vertical overflow drain structure, for example, the amount of accumulation in the vertical transfer register 2 is determined by the potential of the overflow barrier region (hereinafter, simply referred to as OFB region) formed under the vertical transfer register 2.

However, the region below the vertical transfer register 2 also serves as a potential barrier at the time of smear reduction and electronic shutter. It is difficult to design the potential of the OFB region to satisfy all these functions. That is, for example, in order to reduce smear, it is necessary to increase the impurity concentration in the lower portion of the vertical transfer register 2 to form a smear prevention barrier. In this case, however, a desired overflow barrier (potential corresponding to a predetermined accumulation amount) is formed. It becomes difficult to obtain a barrier having levels. Further, when the electronic shutter is performed, it is necessary to increase the impurity concentration of the OFB region under the transfer register or increase the thickness of the OFB region. However, while satisfying such requirements, a desired overflow barrier can be provided. Hard to get.

In the solid-state image pickup device according to this embodiment, the residual signal charges are not discharged through the potential barrier formed in the OFB region under the vertical transfer register 2, but the overflow control gate is passed through the light receiving section 1. The discharge is performed through the portion 5 and the overflow drain 6. In this case, the OFB area under the vertical transfer register 2 and the adjacent channel stopper area do not participate in the weighing.

Therefore, the OFB under the vertical transfer register 2 is
The region and the adjacent channel stopper region can be freely designed according to functions such as smear reduction and a barrier at the time of electronic shutter. Therefore, when applied to the vertical overflow drain structure, good smear characteristics can be maintained,
In addition, a good electronic shutter function can be performed.

[0025]

As described above, according to the driving method of the solid-state image pickup device of the present invention, the charge of the transfer register is discharged by the charge discharging means through the storage section, so that the charge is discharged to the transfer register. It becomes unnecessary to provide means. Therefore, the area of the element is reduced.

Further, in the case of adopting the vertical overflow drain structure, it is not necessary to provide the charge discharging means under the transfer register, so that the degree of freedom in design is secured with respect to the impurity concentration of the semiconductor region under the transfer register and its profile. be able to.

[Brief description of drawings]

FIG. 1 is a potential diagram showing an example of an operation according to an embodiment of a method for driving a solid-state image sensor according to the present invention.

FIG. 2 is a potential diagram of an overflow control gate unit and a light receiving unit for realizing the driving method of the solid-state imaging device according to the present embodiment.

FIG. 3 is a principle configuration diagram of an interline CCD solid-state imaging device.

FIG. 4 is a potential diagram of a conventional solid-state imaging device in a light receiving state and a reading state.

[Explanation of symbols]

 1 Light-receiving part 2 Vertical transfer register 3 Horizontal transfer register 4 Read gate part 5 Overflow control gate part 6 Overflow drain 7 Channel stop area

Claims (2)

(57) [Claims] 1. A storage unit that stores an amount of electric charge according to the amount of incident light, a charge discharging unit that is provided adjacent to the storage unit and discharges the electric charge of the storage unit, and a storage unit that stores the electric charge in the storage unit. A method for driving a solid-state imaging device, comprising: a transfer register configured to transfer the stored electric charge; wherein the electric charge in the transfer register is discharged by the charge discharging unit via the storage unit. . 2. The method for driving a solid-state image pickup device according to claim 1, wherein the charge discharging means has a vertical overflow drain structure.