JPH09321270A - Driving method for charge transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it easy to provide timing in a charge transfer device wherein three charge transfer electrodes are taken as the unit of repetition and one of them functions as a shielding film as well. SOLUTION: Of a set of three charge transfer electrodes G1, G2, G3, G1 and G3 are formed of a polycrystalline silicon film and G2 is formed of an aluminum film so that it functions as a shielding film as well. A constant voltage Vs is applied to G2, and transfer pulses ϕ1a, ϕ2a of a phase dislocated 90 degrees from each other are applied to G1 and G3. This reduces difference in time constant between the charge transfer electrodes as compared with cases where transfer pulses are applied to each of G1 to G3, and thus makes it easy to provide timing.

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 charge transfer device, and more particularly to a method of driving a CCD register.

[0002]

2. Description of the Related Art At present, a solid-state image pickup device used as an input for an electronic still camera or a personal computer uses a device developed for a camera-integrated VTR. Due to the difference between the display method (progressive method) and the display method (progressive method) between the personal computer monitor, signal processing such as conversion of the number of pixels and the scanning method is required. Therefore, there is a need for a solid-state image pickup device that can be easily used as an input for an electronic still camera or a personal computer.

The progressive type solid-state image pickup device has one
It can be realized by using a three-phase drive charge transfer device having three transfer electrodes per pixel. Among such progressive type solid-state image pickup devices, one having a simple structure is disclosed in Japanese Unexamined Patent Publication No. Hei 4 (1999) -1999
-72762 gazette. Hereinafter, this will be described.

FIG. 4 (a) is a block diagram schematically showing a progressive type solid-state image pickup device, FIG. 4 (b) is a plan view showing pixels, and FIG. 4 (c) is XX of FIG. 4 (b). It is a line sectional view.

This solid-state image pickup device has a P-type silicon substrate 1
N-type diffusion layer 2 formed in a stripe shape on the surface portion (may be a P well formed on the surface portion of the silicon substrate)
The surface of the buried channel region made of
A first charge transfer electrode G1 (also serving as a read gate electrode), a second charge transfer electrode G2, and a third charge transfer electrode are traversed through 2, 3-3 (designed to have the same thickness). G3 is provided for transfer pulses φ1, φ2 and φ, respectively.
3 is applied. The third charge transfer electrode G3 is made of a first-layer polycrystalline silicon film, the first charge transfer electrode G1 is made of a second-layer polycrystalline silicon film, and the third charge transfer electrode G3 and the third charge transfer electrode G3 are formed via the insulating film 4. It partially overlaps. The second charge transfer electrode G2 is made of an aluminum film and covers G1 and G3 through the insulating film 5 to prevent light from entering the N type diffusion layer 2 and the P ⁺ type channel stopper 8 in the vicinity thereof. Doubles as Reference ^numeral 6 denotes a photodiode (arranged in rows to form the photoelectric conversion unit 101) formed of an N-type diffusion layer having a P ⁺ -type diffusion layer on its surface, and 7 denotes a read gate region.

FIG. 5 is a time chart showing transfer pulses φ1, φ2 and φ3, and FIG. 6 is a potential diagram for explaining charge transfer.

First, at a timing t1 in the horizontal blanking period, φ1 is a level (hereinafter referred to as “T” level) for conducting a read gate, φ2 is an “H” level, and φ is a φ level.
3 becomes "L" level, the signal charge Q accumulated in the photodiode 6 of each pixel in an arbitrary pixel column
, 1, Q2, Q3, ... Transfer to the N-type diffusion layer 2 under the first charge transfer electrode G1 of each charge transfer device through the read gate region 7.

Next, at a timing t2, when φ1 becomes "H" level, signal charges Q1, Q2, Q3, ...
Part of the signal charges moves to below the adjacent second charge transfer electrode G2, and when φ1 becomes “L” level at the timing t3, the signal charge Q
The movement of 1, Q2 and Q3 below the second charge transfer electrode is completed.

At timing t4, when φ3 is set to the “H” level and φ2 is set to the “L” level, the signal charges Q1 and Q are generated.
2, Q3, ... Move to below the first charge transfer electrodes of the adjacent pixels. The signal charges 61, 62, ..., 63 from the photodiodes at the final stage of each photoelectric conversion unit 101 are transferred to the horizontal charge transfer unit 103.

Next, during the vertical blanking period, the signal charge for one horizontal line is transferred in the horizontal charge transfer section 103, detected by the output circuit 104 as a signal voltage, amplified, and sequentially output as an output voltage Vout. .

A video signal for one field is obtained by repeating the cycle of timings t2 to t6.

[0012]

A driving method of a solid-state image pickup device having such a conventional charge transfer device in a vertical charge transfer portion is a resistance of a polycrystalline silicon film forming first and third charge transfer electrodes. Value (approx. 30 Ω for 0.4 μm film thickness)
/ □) and the resistance value of the metal film (for example, aluminum film) forming the second charge transfer electrode which also serves as the light-shielding film (about 0.03 Ω / □ when the film thickness is 1 μm), so Due to the difference in the constants, different waveforms are blunted between the electrodes and the delay occurs, which causes the problem that occurred, the timing of the pulses did not match, the transfer efficiency of the signal charge in the vertical charge transfer unit deteriorates, and the amount of charge handled decreases. However, there is a drawback that charge transfer itself becomes difficult especially when the transfer frequency is high.

The object of the present invention is to eliminate these drawbacks,
It is an object of the present invention to provide a driving method of a charge transfer device which has a set of three transfer electrodes as a repeating unit capable of high-speed transfer.

[0014]

According to a method of driving a charge transfer device of the present invention, a surface of a channel region in a surface portion of a first conductivity type semiconductor layer on a surface portion of a semiconductor substrate is traversed by an insulating film. A plurality of sets of one charge transfer electrode, a second charge transfer electrode, and a third charge transfer electrode are sequentially arranged, and the second charge transfer electrode is a first charge transfer electrode and a third charge transfer electrode. A method of driving a charge transfer device, which has a lower electric resistance than a charge transfer electrode and also serves as a light blocking film for preventing light from entering the channel region, wherein a predetermined constant voltage is applied to the second charge transfer electrode, A transfer pulse having a phase difference is applied to the first charge transfer electrode and the third charge transfer electrode to transfer the signal charge in the channel region.

In this case, it is preferable to apply transfer pulses having a phase difference of 90 degrees to the first charge transfer electrode and the third charge transfer electrode.

Further, at the time of transferring the signal charge, a constant voltage is set so that the potential of the channel region under the second charge transfer electrode is in the middle of the potential of the channel region under the first or second charge transfer electrode on both sides thereof. It is preferable to set.

Further, one photoelectric conversion unit may be provided for each set of the first charge transfer electrode, the second charge transfer electrode, and the third charge transfer electrode to form the solid-state image pickup device.

Furthermore, the first charge transfer electrode and the third charge transfer electrode may be made of polycrystalline silicon films having different layers, and the second charge transfer electrode may be made of a metal film.

Since the potential of the second charge transfer device having a low electric resistance is fixed, the first and third transfer pulses are applied.
The difference in the time constants of the charge transfer electrodes is reduced.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described.

FIG. 1A is a block diagram schematically showing a progressive-type solid-state image pickup device for explaining an embodiment of the present invention, in which a pixel array including a photoelectric conversion portion 101 and a vertical charge transfer portion 102 is provided. It is the same as the conventional example of FIG. 4 in that it is composed of an image pickup section having a plurality of horizontal lines, a horizontal charge transfer section 103, and an output circuit section 104. A two-phase transfer pulse and a desired constant voltage V _S are applied to the vertical charge transfer section. One stage of the vertical charge transfer unit is arranged corresponding to the structural unit (photodiode) of the photoelectric conversion unit.

An outline of a driving method of a solid-state image pickup device having such a charge transfer device in a vertical charge transfer portion will be described.

First, the photoelectric conversion unit 10 arranged on a plane.
At 1, signal charges are accumulated according to the amount of incident light.

Next, the signal charges 11, 12, 13, 21, 22, 23, 31, 32 of all the photoelectric conversion units 101,
33, 41, 42, 43, 51, 52, 53, 61, 6
2, 63 are read out to the corresponding vertical charge transfer unit 102. Next, transfer pulses φ1a and φ2a having phases different by 90 degrees are applied to the first charge transfer electrode and the third charge transfer electrode which form the vertical charge transfer unit, and a desired constant voltage V _{S is} applied to the second charge transfer electrode. Signal charge 1
1, 12, 13, 21, 22, 23, 31, 32, 3
3,41,42,43,51,52,53,61,6
2, 63 are vertically transferred in each vertical charge transfer unit 102, are sent to the horizontal charge transfer unit 103 for each horizontal line, are transferred in the horizontal charge transfer unit 103 in the horizontal direction, and are output circuit unit 104. Is output via.

As a result, one frame, that is, the signal charges of all the photodiodes are read out.

Next, the structure and operation of the vertical charge transfer section will be described in detail.

FIG. 1B is a plan view showing a cell portion (pixel) of the solid-state image pickup device, and FIG. 1C is a sectional view taken along line XX of FIG.
FIG. 3 is a line cross-sectional view showing a P-type silicon substrate 1, an N-type diffusion layer 2,
The third charge transfer electrode G3 formed of the first-layer polycrystalline silicon film, and the first charge transfer electrode G3 formed of the second-layer polycrystalline silicon film.
Has the same charge transfer electrode G1 and the second charge transfer electrode G2 which also functions as a metal light-shielding film. The structure is the same as that of FIG. 4, but the first to third charge transfer electrodes have φ1a, V _S , φ2a
There is a difference in applying.

FIG. 2 is a time chart for explaining one embodiment of the present invention, and FIG. 3 is a potential diagram for explaining charge transfer.

At the timing t1 of the horizontal blanking period, φ2a becomes “L” level and φ1a becomes “T” level, and the signals read from the arbitrary photoelectric conversion units 101 to the vertical charge transfer units 102 of the same pixel column, respectively. Charge Q1
, a are stored under the first charge transfer electrode G1 to which the read voltage V _T is applied. Next, at the timing t2, the signal charges Q1a, Q2a, Q3a, ... Are still accumulated below the first charge transfer electrode G1 to which the high voltage V _H is applied, even if φ1a becomes “H” level. is there. Similarly, the timing t3
, When φ1a becomes “L” level, the signal charge Q
, 1 move to below the second charge transfer electrode G2 to which the constant voltage V _S is applied, move to below the third charge transfer electrode G3, and at timing t5, φ1a becomes “H” level. Then, the third charge transfer electrode G3 and the first pixel
Of the first charge transfer electrode G1 at the timing t6 when φ2a becomes “L” level.
Move down one by one.

Thereafter, the signal charges are transferred through the vertical charge transfer section by repeating the timings from t2 to t6.

A constant voltage V _S (V _L <V _S <V _H ) is applied to the second charge transfer electrode having a low resistance value, which is made of a polycrystalline silicon film and has a relatively high electric resistance. Since the transfer pulses .phi.1a and .phi.2a are applied to the charge transfer electrodes of No. 3, there is not much difference in time constant, and the timing is easy to take. Therefore,
It is possible to avoid a decrease in transfer efficiency or the amount of charge handled (the maximum amount of charge that can be transferred), and high-speed transfer becomes possible. In addition, since it is a two-phase drive, the drive circuit becomes simple.

The first and third charge transfer electrodes are connected in each row (horizontal) direction, and the second charge transfer electrodes are divided for each column (actually, one end is commonly connected to V. _S
However, the second charge transfer electrodes may also be connected in each row direction.

Further, although the case of having the buried channel type vertical charge transfer portion has been described, it goes without saying that the present invention can also be applied to the surface channel type. Further, the present invention can be applied not only to the solid-state image pickup device but also to a simple charge transfer device.

The pulse phase difference is most preferably 90 degrees, but charge transfer is possible at any value less than 180 degrees and more than 0. Therefore, it is desirable considering the allowable range of characteristics and manufacturing variations. It is obvious that the value of should be designed without needing to explain it in detail again.

[0035]

According to the driving method of the charge transfer device of the present invention, a constant voltage is applied to the second charge transfer electrode which also serves as a light shielding film having a low resistance value, and the first and third charge transfer devices having a high resistance value are transferred. Since transfer pulses whose phases are shifted from each other are applied to the electrodes, the transfer pulses are applied, so the difference in the time constants of the charge transfer electrodes to which the transfer pulses are applied becomes small, the timing is easily adjusted, and the transfer efficiency and the maximum transferable charge Prevent a decrease in quantity,
This has the effect of enabling high-speed transfer.

[Brief description of drawings]

FIG. 1 is a block diagram (FIG. 1A) schematically showing a progressive-type solid-state imaging device for explaining an embodiment of the present invention, and a plan view showing pixels (FIG. 1).
(B)), and the XX sectional view taken on the line of FIG.
(C)).

FIG. 2 is a time chart for explaining an embodiment of the invention.

FIG. 3 is a potential diagram for explaining an embodiment of the present invention.

FIG. 4 is a block diagram schematically showing a progressive-type solid-state imaging device for explaining a conventional example (FIG. 4).
FIG. 4A is a plan view showing a pixel (FIG. 4B) and FIG.
The XX sectional view taken on the line (b) (FIG.4 (c)).

FIG. 5 is a time chart for explaining a conventional example.

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

[Explanation of symbols]

1 P-type silicon substrate 2 N-type diffusion layer 3-1, 3-2, 3-3, 4, 5 Insulating film 6 Photodiode 7 Outflow gate region 8 P ⁺ type channel stopper 11-61, 12-62, ..., 13-63 signal charge 101 photoelectric conversion unit (photodiode array) 102 vertical charge transfer portion 103 horizontal charge transfer portion 104 output circuit φ1, φ1a, φ2, φ2a, φ3 transfer pulse V _S constant voltage

Claims (5)

[Claims] 1. A first charge transfer electrode, a second charge transfer electrode, and a third charge transfer electrode which traverse the surface of a channel region on the surface of a first conductivity type semiconductor layer on the surface of a semiconductor substrate through an insulating film, respectively. A plurality of sets of charge transfer electrodes are sequentially arranged, and the second charge transfer electrode has a lower electric resistance than the first charge transfer electrode and the third charge transfer electrode, and light is incident on the channel region. A method of driving a charge transfer device which also serves as a light-shielding film for preventing the above-mentioned charge transfer, comprising applying a predetermined constant voltage to the second charge transfer electrode, and applying the same to the first charge transfer electrode and the third charge transfer electrode. A method of driving a charge transfer device, comprising applying a transfer pulse having a phase difference to transfer signal charges in the channel region. 2. The method of driving a charge transfer device according to claim 1, wherein transfer pulses having a phase difference of 90 degrees are applied to the first charge transfer electrode and the third charge transfer electrode. 3. A constant voltage is set so that the potential of the channel region under the second charge transfer electrode is intermediate between the potentials of the channel regions under the first or second charge transfer electrodes on both sides of the second charge transfer electrode during the transfer of the signal charges. The method for driving the charge transfer device according to claim 1, wherein the setting is performed. 4. The solid-state imaging device according to claim 1, wherein one photoelectric conversion unit is provided for each set of the first charge transfer electrode, the second charge transfer electrode, and the third charge transfer potential to form a solid-state imaging device. 4. The method for driving the charge transfer device according to item 3. 5. The first charge transfer electrode and the third charge transfer electrode are formed of a polycrystalline silicon film having different layers, and the second charge transfer electrode is formed of a metal film. Driving method of the electric charge transfer device.