JPH02161879A - Driving method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To reduce a dark current by setting a pulse supplied to a gate which combines a read-out gate and a transfer gate in a non-vertical transfer period for occupying a period of the greater part in one horizontal period, to an 'L' level. CONSTITUTION:At the time of t=t1, a pulse phiG11, a pulse phiG12, a pulse phiG13, and a pulse phiG14 are in middle level ('M'), a high level ('H'), a middle level ('M'), and a low level ('L'), respectively. At the time of t=t2, read-out of a signal charge in a first field is executed, therefore, the pulses phiG11, phiG13 go to 'H', and a signal charge of a photodiode 1 is read out. Subsequently, at the time of t=t3, the pulses phiG11 and the pulse phiG13 go to 'L', the pulse phiG12 and the pulse phiG14 go to 'L', and the signal charge is accumulated under the gate of the electrodes G12, G14, and transferred in the one-stage vertical direction in a period extending from t=t4 to t5. In such a way, a dark current can be reduced remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for driving a solid-state imaging device that can be used in an integrated video camera or the like.

2. Description of the Related Art In recent years, solid-state imaging devices have been widely put into practical use, such as in the imaging section of an integrated video camera.

Hereinafter, a conventional method for driving a solid-state imaging device will be described with reference to the drawings.

FIGS. 2 and 3 are block diagrams of a solid-state imaging device and pulse waveforms used in a conventional driving method for driving the solid-state imaging device.

In Figure 2, 1 is a photodiode with a photoelectric conversion function, 2 is an enhancement MO8 type transistor that functions as a readout gate for reading out the signal of photodiode 1, and 3 is a buried channel structure that transfers signal charges in the vertical direction. A vertical transfer section, 4 is a vertical transfer gate that controls vertical transfer, 5 is a horizontal transfer section that transfers signal charges in the horizontal direction, and 6 is an output section.

The vertical transfer section has a 1-bit configuration including four transfer gates adjacent in the vertical direction l\, and has two readout gates per 1 bit. Furthermore, electrodes G1 to G4 for applying pulses are connected to the transfer gate forming each bit, and the readout gate 2 is also connected to the electrodes G1 and 63.

FIG. 3 shows the above electrodes Gl, G2*G3 and G
4. Pulse φG 31 rφG32. φG33
and φG34 timing chart,
The pulse φ(11 applied to the electrode GI and the pulse φG33 applied to the electrode G3 control readout and transfer, and readout is performed when it is at a high level, and transfer is performed when it is at a middle level and a low level.

Pulse φG32 applied to electrode G2 and pulse φG34 applied to electrode G4 control transfer, and transfer is performed at high level and low level.

The operation of the conventional solid-state imaging device configured as described above under the driving method will be described.

First, time 1=1. When , pulse φG31 is at middle level (hereinafter abbreviated as “M”), pulse φG32 is at high level (hereinafter abbreviated as “H”), and pulse φG33 is at M″.
, pulse φG34 is at a low level (hereinafter abbreviated as "L"), and these pulses are applied to each electrode 01 to G4 to prepare for signal reading. Then 1=
At 12, pulses φG31 and φG33 become “H” in order to read the signal charge in the first field.
Therefore, the signal charge of the photodiode 1 is read out to the channel under the gate of the vertical transfer section connected to the electrodes G and G3. Next, vertical transfer is performed between t=t3 and 1-t4. Next, at tt5, pulse φG3
1 and pulse φG33 is “H” Pulse φG32 is “H”
", and the pulse φG34 becomes "L" to prepare for reading the second field. Then, when t=ts, the pulse φG3 and the pulse φG33 become "H", and the signal charge of the photodiode 1 is transferred to the electrodes G1 and 63. Read out to the channel below the gate of the vertical transfer section connected to.

Thereafter, drive control for repeating transfer and reading is executed in the same manner. Note that the pulses φG31 to φG shown in FIG.
The timing at times other than times t4 and t5 in No. 34 is shown in a partially enlarged manner, and the change point of the logic level is shifted.

Problems to be Solved by the Invention However, in the conventional driving method of a solid-state imaging device, -
The non-vertical transfer period (1
, + and t5), the G1 gate readout electrode, which also serves as the readout gate and transfer gate, is set to "M", and there are many depletion layers at the interface formed under the photodiode 1 and 61 gates. Dark current is generated through generation centers such as existing interface states, and there are problems in that dark current increases particularly during high-temperature operation and fixed pattern noise occurs due to variations in dark current.

Means for Solving the Problems In order to solve the above problems, the present invention provides a one-dimensional or two-dimensional
A photoelectric conversion unit having a photoelectric conversion function arranged in a dimension, a transfer unit that transfers charges generated in the photoelectric conversion unit, and a transfer unit and the photoelectric conversion unit are coupled to control readout of charges. When driving a solid-state imaging device constituted by a readout switch unit, the voltage applied to the readout switch unit is configured to read a voltage having a polarity opposite to that when the charge is read out when the charge is not read out. It is configured by applying voltage to the switch section.

Effect With the above configuration, when charges are not read out, a reverse bias voltage is applied to, for example, the P-type substrate, and a hole accumulation layer is formed under the readout electrode, preventing a depletion layer from spreading at the interface. It disappears. Therefore, the dark current generated by the generation center such as the interface level of the read gate is significantly reduced.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a pulse waveform for realizing a method for driving a solid-state imaging device according to a first embodiment of the present invention.

In Fig. 1, φG11 is the readout/transfer pulse waveform applied to electrode G+, φG12 is the transfer pulse waveform applied to electrode G2, φG+3 is the readout/transfer pulse waveform applied to electrode G3, and φG+4 is the readout/transfer pulse waveform applied to electrode G4. This is a transfer pulse waveform electrode.

In the driving method of the solid-state imaging device of the present invention, first, the old pulse φG of the time signal LH is set to the middle level (hereinafter abbreviated as "M").
, pulse ψG12 is at a high level (hereinafter abbreviated as “■]°゛), pulse φGia is “M”, pulse φG is at a low level (hereinafter abbreviated as “I7゛°), and these pulses are connected to each electrode GH= G4 is applied to prepare for signal reading. Next, in order to read out the signal charge IJ in the 6th field at t=t2, the pulses φG and φG 13 become "■]", and the discharged charge of the photodiode 1 is read out. Next, when t=ta, the pulse φ becomes 11 and the pulse ψG+3 becomes °'L", the pulse φG12 and the pulse φG4 become °L", and the signal charge is accumulated in the area below the gates of the electrodes G2 and Gl.Next, tt
The data is transferred in the vertical direction during the period from 4 to t5.

Thereafter, drive control for repeating transfer and reading is executed in the same manner.

As described above, in this embodiment, in the non-vertical transfer period that occupies most of the horizontal period, the transfer gate voltage applied to the G, which serves as the read gate and the transfer gate, the gate, and the G3 gate is The level of pulse φGll and pulse φG13 applied to G+Agate and 63 gates, which also serves as “L”
As mentioned above, the dark current that occurs at the boundary with the photodiode 1 under the readout electrode is less likely to occur.

Effects of the Invention The present invention has the following advantages: - During the non-vertical transfer period that occupies most of the horizontal period, the pulse applied to the gate that serves as both the read gate and the transfer gate is set to "L". By doing so, it is possible to significantly reduce the dark current, which has great practical effects.

Although a two-dimensional image sensor is used as an example in this embodiment, it goes without saying that the same effect can be obtained with a one-dimensional image sensor.

[Brief explanation of the drawing]

FIG. 1 is a drive pulse waveform diagram in an embodiment of the present invention, FIG. 2 is a configuration diagram of a solid-state imaging device to which the drive method in the embodiment of the present invention is applied, and FIG. 3 is a conventional drive pulse waveform diagram. . ]... Photodiode, 2... Readout gate, 3... Vertical transfer section, 4...
・Vertical transfer gate, 5...Horizontal transfer section, 6...
...Output section, 7...Image area, 8.
...Storage section, Gl, G2, G3G4...
...Electrode, φG ro, φG I3, φG 31 *
φG33・・・Reading and transfer pulse waveform, φG
32. φG34゜φGI2. φG 14...Transfer pulse waveform.

Claims (1)

[Claims] (1) A photoelectric conversion unit having a photoelectric conversion function arranged in one or two dimensions, a transfer unit that transfers the charges generated in the photoelectric conversion unit, and a transfer unit that transfers the charges generated in the photoelectric conversion unit, and the transfer unit and the photoelectric conversion unit are combined to charge When driving a solid-state imaging device configured with a readout switch section that controls readout of the charge, the polarity of the voltage applied to the readout switch section is such that the polarity of the voltage applied to the readout switch section is opposite to that when reading out the charge. 1. A method for driving a solid-state imaging device, characterized in that a voltage is applied to the readout switch section during a predetermined period during non-readout.