JP2987844B2 - Solid-state imaging device and driving method thereof - Google Patents

Description

The present invention relates to a frame interline transfer in which signal charges are transferred from a plurality of light receiving units to a vertical transfer unit, and the signal charges are transferred to a horizontal transfer unit and output. The present invention relates to a (FIT) type solid-state imaging device and a method of driving the device.

[Summary of the Invention]

The present invention relates to a frame interline in which signal charges are read from a light receiving section to a vertical transfer section, the signal charges are transferred from the vertical transfer section to a storage section at a high speed, and the signal charges are output via a horizontal transfer section. In the transfer type solid-state imaging device, a linear overflow drain is provided in the light receiving unit, and the transfer speed at which unnecessary charges existing in the vertical transfer unit are swept is increased by the vertical transfer unit. By making the transfer speed higher than the transfer speed, the transfer efficiency and the amount of charges handled in the vertical transfer unit are improved.

[Prior Art] CCD of frame interline transfer type (hereinafter, FIT type)
Is to provide a storage unit between the vertical transfer unit and the horizontal transfer unit of an interline transfer type (hereinafter, IT type) CCD, and to transfer signal charges to the storage unit at high speed, thereby reducing smear. (For example, see Japanese Patent Application Laid-Open No. 56-8966).

Here, FIGS. 4 and 5 show a conventional FIT type CCD.
This will be described with reference to the drawings. FIG. 4 is a diagram showing a configuration of a general FIT type CCD. In the FIT type CCD 50, as shown in FIG. 4, a plurality of light receiving sections 51 for converting incident light into signal charges are arranged in a matrix. A vertical transfer unit 52 is provided for each column along the vertical column of the light receiving unit 51. The vertical transfer unit 52 is connected to a storage unit 54 via a transfer gate 53. A horizontal transfer unit 55 is provided at the end of the storage unit 54, and the horizontal transfer unit 55 outputs data for each horizontal line. Storage unit 54 of vertical transfer unit 52 of this CCD 50
A drain portion 56 is provided at the end opposite to. The drain portion 56 is a region for absorbing unnecessary charges.

FIG. 5 is a waveform diagram showing the operation of the CCD 50. The signal (a) is a signal corresponding to a television signal, a low level period is a vertical blanking period _tBLX , and a high level period is video. The period is t _VD . The signal (b) is a CCD
5 shows vertical drive pulses. The vertical drive pulse will be described. The period t ₁ in the vertical blanking period t _BLX is described.
Then, the vertical transfer unit 52 enters the reverse transfer state, and the vertical transfer unit 52
A so-called sweep transfer in which unnecessary charges in the inside are transferred toward the drain portion 56 is performed. Next, read pulse Φ
_RO is supplied to the readout gate of each light receiving unit 51, and signal charges are supplied from each light receiving unit 51 to the vertical transfer unit 52. After the read, in the period t ₂ in the vertical blanking period t _BLX, the read signal charge is frame transfer at high speed from the vertical transfer unit 52 to the storage section 54. Here, the frequency of the driving pulse for the high-speed frame transfer is about 900 kHz, which is the same frequency as the sweep transfer. The direction of the frame transfer is forward transfer. In the video period t _VD , a pulse Φ _LS for line shift is supplied to output for each horizontal line, and an image signal is output from the horizontal transfer unit 55.

Also, a technique is known in which the sweep transfer of unnecessary charges is performed by positive transfer, which is the transfer direction of signal charges, without performing reverse transfer.For example, Japanese Patent Application Laid-Open No. 58-10977 discloses a technique of sweep transfer by forward transfer. Are listed.

[Problems to be solved by the invention]

Such a FIT-type CCD 50 is compared with an IT-type CCD,
Smearing can be reduced, and it is desirable to increase the transfer frequency in order to reduce the smear level.

However, when the frame transfer of the signal charge to the storage unit 54 is performed at a high frequency of about 900 kHz, the vertical transfer efficiency is reduced, and the transfer efficiency is reduced, so that image defects are likely to occur. In such a frame transfer, the amount of charge handled by the vertical transfer unit 52 is reduced, and characteristics such as a reduction in dynamic range are caused.

In view of the above technical problems, it is an object of the present invention to provide a solid-state imaging device and a method of driving the device, which reduce smear and prevent deterioration of characteristics due to high-speed transfer.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a plurality of light receiving units arranged in a matrix, and a vertical transfer unit provided along a vertical column of these light receiving units to sweep out unnecessary charges of each of the light receiving units. Having a vertical or horizontal overflow drain structure, after high-speed sweeping and transferring unnecessary charges present in the vertical transfer section, reading out signal charges obtained in the respective light receiving sections to the vertical transfer section, and immediately thereafter, A solid-state imaging device that transfers a signal charge, which is an image signal read to a vertical transfer unit, to a position adjacent to the horizontal transfer unit in the vertical transfer unit at a high speed, and then outputs the signal charge for each horizontal line via the horizontal transfer unit. In the device, high-speed sweep transfer of unnecessary charges existing in the vertical transfer unit and signal charges to be image signals read by the vertical transfer unit up to a position adjacent to the horizontal transfer unit in the vertical transfer unit The high-speed transfer is performed during the vertical blanking period, and the speed at which the unnecessary charges existing in the vertical transfer unit are swept out at high speed is transferred to the vertical transfer unit. The speed is higher than the speed of high-speed transfer to the position adjacent to the horizontal transfer unit.

Further, the present invention provides a plurality of light receiving units arranged in a matrix and a vertical transfer unit provided along a vertical column of these light receiving units, and a vertical or horizontal type for sweeping out unnecessary charges of each of the light receiving units. After having an overflow drain structure and performing high-speed sweep transfer of unnecessary charges existing in the vertical transfer portion,
The signal charges obtained in each of the light receiving sections are read out to the vertical transfer section, and immediately thereafter, the signal charges serving as the image signals read out to the vertical transfer section are rapidly transferred to a position adjacent to the horizontal transfer section in the vertical transfer section. Transferring the signal charges through the horizontal transfer unit for each horizontal line, and then transferring the unnecessary charges in the vertical transfer unit at high speed, and reading out the unnecessary charges in the vertical transfer unit to the vertical transfer unit. The high-speed transfer of the signal charges that become the image signals to the horizontal transfer unit adjacent position in the vertical transfer unit is performed during the vertical blanking period, and the high-speed sweeping transfer of the unnecessary charges existing in the vertical transfer unit is performed as described above. The signal transfer is performed at a higher speed than the speed at which the signal charges serving as the image signals read by the vertical transfer unit are transferred at high speed to a position adjacent to the horizontal transfer unit in the vertical transfer unit.

Further, in the method for driving a solid-state imaging device according to the present invention, the high-speed sweeping transfer of the unnecessary charges existing in the vertical transfer unit and the signal transfer as an image signal read out to the vertical transfer unit may be performed in the vertical transfer unit. The high-speed transfer to the position adjacent to the horizontal transfer unit is performed within a fixed period that is interposed with the period in which the read pulse is supplied.

[Action]

Compared to a solid-state imaging device having a structure in which unnecessary charges are positively swept through a vertical transfer unit, a solid-state imaging device having a structure in which unnecessary charges in each light receiving unit are swept out without passing through a vertical transfer unit has a vertical transfer function. The amount of unnecessary electric charge that is swept out using the unit becomes small. For this reason, even if the sweep transfer itself is speeded up, sufficient sweeping of unnecessary charges can be realized. Due to such a high speed of the sweep transfer, in the vertical blanking period, which is a fixed period, the time for transferring the signal charge from the vertical transfer unit to the storage unit can be lengthened, and the transfer speed is reversed. By reducing the speed, the vertical transfer efficiency can be improved.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

In this embodiment, the FIT (frame interline transfer) type C
This is an example of a CD in which the frequency of the sweep transfer of the positive transfer is higher than the frequency of the vertical frame transfer of the signal charge by about 2
This is an example of a CCD that is doubled.

First, FIG. 2 shows the entire block structure. The CCD 1 according to the present embodiment includes a plurality of light receiving units 4 including photo sensors arranged in a matrix and a first vertical register unit 5 as a vertical transfer unit so as to configure the imaging unit 2.
The light receiving section 4 has a cross-sectional structure described later, and has a vertical overflow drain structure for sweeping unnecessary charges to the substrate. The first vertical register section 5 is formed along each vertical column of the light receiving section 4. A transfer gate for reading out signal charges is provided between each light receiving section 4 and the first vertical register section 5. Transfer signals IMΦ1 to IMΦ4 are supplied to the first vertical register section 5, respectively.
The charge of the first vertical register section 5 is transferred by the pulses IMΦ1 to IMΦ4. As will be described later, the frequency of the pulses of the transfer signals IMΦ1 to IMΦ4 is set to be high when sweeping and transferring unnecessary charges and to be low when transferring frame charges of signal charges.

In the CCD 1 of the present embodiment, the first vertical register 5
The accumulation section 3 is formed continuously. The storage unit 3 includes a second vertical register unit 6 provided for each vertical column corresponding to the first vertical register unit 5 provided for each vertical column. The signal charges are frame-transferred from the first vertical register section 5 to the second vertical register section 6 at high speed, and the signal charges are temporarily stored. The second vertical register unit 6 is supplied with four-phase transfer signals STΦ1 to STΦ4.
Of the vertical register section 6 is transferred.

On the opposite side of the second vertical register section 6 from the first vertical register section 5, a horizontal register section 7 is provided. The horizontal register unit 7 is a register for reading out the electric charges accumulated in each second vertical register unit 6 of the accumulation unit 3 for each horizontal line. Charges for one horizontal line are transferred from all the second vertical register units 6 to the horizontal register unit 7, and the charges are output to the output circuit 8. The horizontal register unit 7 includes two-phase transfer signals HΦ1, HΦ2
Is supplied, and the transfer is performed by the transfer signals HΦ1 and HΦ2.

From the horizontal register section 7, a signal is extracted to an output circuit 8 having a configuration such as a source follower through a floating diffusion 10f located at the end of the horizontal register section 7. Reset is performed by the reset transistor 10, by the precharge gating signal ΦPG supplied to the gate of the reset transistor, the on-off between the floating diffusion 10f and the precharge voltage V _PD and the reset drain 10d for reset Is controlled. Then, the image signal V _{OUT of the} CCD 1 is output from the output terminal 9 of the output circuit 8.

FIG. 3 shows a sectional structure of the light receiving section 4 and the first vertical register section 5. The CCD 1 is formed on an n-type silicon substrate 11, and a light receiving section 4 and a first vertical register section 5 are formed in a p-type first well region 12 formed on the n-type silicon substrate 11. Is done.

The light receiving section 4 is constituted by a photosensor using an n-type impurity region 13 in the p-type first well region 12, and a hole accumulation layer 14 is formed on the surface of the n-type impurity region 13. Is done. In the light receiving section 4, the light shielding film 15 made of an aluminum film is removed, and light enters through the opening 16 thereof. The CCD 1 has a vertical overflow drain structure as a structure for sweeping out unnecessary charges of each light receiving unit 4 without passing through the first vertical register unit 5. Therefore, the substrate voltage
By changing Vsub, unnecessary charges of the light receiving section 4 can be swept out to the n-type silicon substrate 11.

The vertical register section 5 uses a polysilicon layer covered with the light shielding film 15 on the thin polysilicon film 17 and covered with the silicon oxide film 18 as the transfer electrode 19. Although not shown, the transfer electrode 19 has a multilayer structure. A silicon oxide film 21 is provided below the transfer electrode 19 via a silicon nitride film 20,
The n-type impurity region below the substrate surface becomes a buried channel region 22 to which signal charges are transferred. Below the buried channel region 22, a p-type second well region 23 for preventing smear is formed. The light receiving portion 4 side of the buried channel region 22 is separated from the n-type impurity region 13, and the separated region becomes a transfer gate 24. On the opposite side of the buried channel region 22 from the light receiving portion 4 side, a channel stopper region 25 is formed along the light receiving portion 4 of another row so as to face the substrate surface.

In the CCD 1 of this embodiment having such a structure, the frequency of the high-speed signal charge frame transfer is set to half the frequency of the unnecessary charge sweep-out transfer. For this reason, the vertical transfer efficiency and the amount of charges handled can be improved. The direction of the sweep transfer of the vertical register section 5 is positive transfer, and the unnecessary charges are swept without requiring a special drain for absorbing the unnecessary charges.

The operation of the CCD 1 will be described with reference to FIG. The signal (a) is a signal corresponding to a television signal. The low-level period is a vertical blanking period T _BLK and the high-level period is a video period _TVD . The signal (b) indicates a vertical drive pulse of the CCD. First, when the vertical blanking period T _BLK starts, sweep transfer of unnecessary charges is performed. The unnecessary charge discharging transfer is unnecessary charges swept transfer present in the first vertical register section 5 is carried out at 1.2MHz frequency f ₁ to the transfer period T ₁ sweep.

Here, this sweep transfer is performed as a forward transfer, and is transferred from the first vertical register unit 5 to the horizontal register unit 7 via the second vertical register unit 6. This unnecessary charge is, for example, the reset drain 10 of the reset transistor 10.
Swept out to d. Unnecessary charges that are swept out by such positive transfer include smear charges accumulated in the first vertical register section 5 because only the dark signal charges because the receiving section 4 itself has a vertical overflow drain structure. And the charge itself is not large. Therefore, in the positive transfer, unnecessary charges can be swept out without requiring a special drain. Further, since no many charge amount of unnecessary charges, allow sufficient sweep transfer at a high frequency f _1. Further, the transfer efficiency is easily improved because the forward transfer is swept out, and a mechanism for the reverse transfer is not required.

After this sweep transfer period T _1, a read pulse Φ
_RO is supplied to required electrodes of the transfer electrodes IMΦ1 to IMΦ4,
The signal charges are read from the light receiving unit 4 to the first vertical register unit 5 via the transfer gate 24.

After the read operation of the signal charge, in the same vertical blanking period T _BLK, the frame transfer of signal charges is performed during a frame transfer period T _2. In this frame transfer, signal charges are transferred from the first vertical register section 5 to the second vertical register section 6. The frame transfer period T ₂ are, frame transfer is performed at a transfer frequency f ₂ of 600kHz, this frequency f ₂ is the transfer electrodes IMΦ1~IMΦ4 and STΦ1~STΦ4 driven. Turning now to compare the frequency f ₂ of the frequency f ₁ and frame forwarding of the aforementioned sweep transfer, the frequency f ₁ of the transfer sweep is a 1.2MHz, the frequency f ₂ of the frame forwarding
Since it is 600 kHz, the frame transfer speed is set to half of the sweep transfer speed. Therefore, the CCD of the present embodiment
In this case, it is possible to prevent the vertical transfer efficiency from deteriorating, and to increase the amount of charges handled. Also, since the frequency of frame transfer is reduced in the process,
It is not necessary to lower the resistance of the transfer electrode.

Frame transfer period in which such frame transfer is performed
After T _2, the video period T _VD, the signal [Phi _LS for line shift is supplied to the second vertical register section 6, the signal charges of the storage part 3 is transferred to the horizontal register section 7 for each horizontal line You. The frequency of this signal Φ _LS is 15.7 kHz. Then, charges are transferred in the horizontal direction from the horizontal register unit 7 by the transfer signals HΦ1 and HΦ2, and the image signal _VOUT is output via the floating diffusion 10f and further via the output circuit 8.

CCD1 such this embodiment has a structure having a vertical overflow drain to the light receiving unit 4, in order to lower smear reduction is made, it can be a frequency higher the frequency f ₁ of transfer sweep. Therefore, the frame transfer frequency f ₂
, The vertical transfer efficiency can be improved, and the amount of charge handled can be improved. Furthermore, since a lower frequency is sufficient, the necessity for lowering the resistance of the transfer electrode and the like is reduced.

Further, with the vertical overflow drain structure, unnecessary charges themselves can be reduced in amount, and sweep transfer can be performed by positive transfer, so that charges can be swept to the output section. For this reason, it is not necessary to provide a drain for absorbing a special charge, and the frame transfer and the sweep transfer are in the same direction, so that the transfer efficiency is easily improved, and a mechanism for reverse transfer is also unnecessary.

In the above-described embodiment, the transfer direction of the sweep transfer is the positive transfer. However, a drain is provided on the side of the first vertical register section 5 opposite to the second vertical register section 6, and unnecessary charges are discharged to the drain. Reverse transfer can also be performed. Instead of transferring unnecessary charges to the output unit, a charge absorption unit may be provided in the middle of the positive transfer and may be swept out there.
Further, in the above-described embodiment, the vertical overflow drain structure is used as a structure for sweeping out unnecessary charges of each light receiving unit without passing through the vertical transfer unit. However, a horizontal overflow drain structure may be used. Further, sweep the frequency f ₁ of the transfer 1.2M
Hz, but the frequency f ₂ of the frame transfer of signal charges was 600kHz, but is not limited to these frequencies.

〔The invention's effect〕

As described above, according to the present invention, the speed of the sweep transfer can be increased, and the speed of the transfer for transferring the signal charges from the vertical transfer unit to the storage unit at a relatively high speed can be relatively reduced. For this reason,
It is possible to improve the vertical transfer efficiency and the amount of charges handled, and it is not necessary to add a special step for reducing the resistance of the transfer electrode in the process.

[Brief description of the drawings]

FIG. 1 is a waveform diagram for explaining the operation of an example of the solid-state imaging device according to the present invention, FIG. 2 is a block diagram showing the overall configuration of the example, and FIG. It is sectional drawing which shows the cross-sectional structure of a part. FIG. 4 is a block diagram of an example of a conventional FIT type CCD.
FIG. 5 is a waveform chart of one example of the related art of FIG. DESCRIPTION OF SYMBOLS 1 ... CCD 2 ... Image pick-up part 3 ... Storage part 4 ... Light-receiving part 5 ... First vertical register part 6 ... Second vertical register part 7 ... Horizontal register part 8 ... Output circuit _TBLK …… Vertical blanking period T ₁ … Swept transfer period T ₂ …… Frame transfer period

Claims (3)

(57) [Claims] 1. A plurality of light receiving sections arranged in a matrix,
A vertical transfer section is provided along a vertical column of these light receiving sections,
A vertical or horizontal overflow drain structure for sweeping out unnecessary charges of each of the light receiving sections, and after performing high-speed sweep transfer of unnecessary charges existing in the vertical transfer section, the signal charges obtained in each of the light receiving sections are The signal charges, which are read into the vertical transfer unit and immediately thereafter become the image signals read out to the vertical transfer unit, are transferred at high speed to a position adjacent to the horizontal transfer unit in the vertical transfer unit, and thereafter, the signal charges are transferred for each horizontal line. In the solid-state imaging device that outputs via the horizontal transfer unit, high-speed sweep transfer of unnecessary charges existing in the vertical transfer unit, and signal charges in the vertical transfer unit that serve as image signals read out to the vertical transfer unit in the vertical transfer unit. High-speed transfer to a position adjacent to the horizontal transfer unit is performed during the vertical blanking period, and the speed at which high-speed sweep transfer of unnecessary charges existing in the vertical transfer unit is transferred to the vertical transfer unit. The solid-state imaging device, characterized in that the signal charges as an image signal Desa seen is faster than the speed of high-speed transfer to the horizontal transfer section adjacent positions in the vertical transfer portion. 2. A plurality of light receiving units arranged in a matrix,
A vertical transfer section is provided along a vertical column of these light receiving sections, and has a vertical or horizontal overflow drain structure for sweeping out unnecessary charges of each of the light receiving sections. After the sweep transfer, the signal charges obtained in the respective light receiving units are read out to the vertical transfer unit, and immediately thereafter, the signal charges serving as image signals read out to the vertical transfer unit are horizontally transferred in the vertical transfer unit. A high-speed transfer to a position adjacent to the vertical transfer unit, and thereafter, the signal charge is output for each horizontal line via a horizontal transfer unit. High-speed transfer of signal charges, which become image signals read to the transfer unit, to a position adjacent to the horizontal transfer unit in the vertical transfer unit is performed during a vertical blanking period. The high-speed sweep transfer of unnecessary charges existing in the vertical transfer unit is performed at a higher speed than the speed at which the signal charges serving as image signals read to the vertical transfer unit are transferred at high speed to a position adjacent to the horizontal transfer unit in the vertical transfer unit. Driving method of the solid-state imaging device. 3. A plurality of light receiving units arranged in a matrix,
A vertical transfer section is provided along a vertical column of these light receiving sections, and has a vertical or horizontal overflow drain structure for sweeping out unnecessary charges of each of the light receiving sections. After the sweep transfer, the signal charges obtained in the respective light receiving units are read out to the vertical transfer unit, and immediately thereafter, the signal charges serving as image signals read out to the vertical transfer unit are horizontally transferred in the vertical transfer unit. A high-speed transfer to a position adjacent to the vertical transfer unit, and thereafter, the signal charge is output for each horizontal line via a horizontal transfer unit. The high-speed transfer of the signal charge, which becomes the image signal read to the transfer unit, to a position adjacent to the horizontal transfer unit in the vertical transfer unit is determined by interposing a period in which a read pulse is supplied. A high-speed sweeping transfer of unnecessary charges existing in the vertical transfer unit is performed within a predetermined period, and a signal charge which is an image signal read to the vertical transfer unit is transferred to a horizontal transfer unit in the vertical transfer unit. A driving method for a solid-state imaging device, wherein the driving is performed at a higher speed than a speed at which the data is transferred to an adjacent position.