JPS60134676A - Method of driving solid-state image pickup device - Google Patents

Abstract

PURPOSE:To prevent boundary level from becoming generating source of dark current by repeating action of sweeping out unnecessary charge and action of making the surface of peripheral area of a photo-detector accumulation state in each light receiving period at one horizontal period. CONSTITUTION:The photo-detector 1 at the time of reading is reset to voltage Vh (for instance +10V) of a reading gate section 3, and voltage of electrodes P1-P4 at the time of light receiving is made shallower voltage Vm1 (for instance +8V) than Vh, and signal charge is accumulated in the detector 1. At this time, generated charge exceeding Vm1 flows into vertical register side. In this case, scanning period out of one horizontal period makes voltage applied to vertical transfer electrodes P1-P4 to Vm1, however, in fly-back line period, electrodes P1-P4 are made low level, for instance -5V. Thus, dark current generated from a channel stopper 2 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a novel method for driving a solid-state imaging device, and in particular to a method for driving a solid-state imaging device in which a vertical register is used as a transfer register in time division or as an overflow drain. The present invention aims to provide a novel method for driving a solid-state imaging device that can reduce current.

BACKGROUND TECHNOLOGY AND PROBLEMS A solid-state imaging device using a charge transfer device such as a charge coupled device (hereinafter referred to as RCCDJ) has a photosensitive section in which photodetectors are arranged and a transfer register corresponding to the photosensitive section. There is a configuration in which pairs of are arranged vertically. A good example is the vertical interline transfer type, which also has a storage section (
It plays almost the same role as the storage section installed in parallel with the photosensitive section in the frame transfer type. ) is also included.

Incidentally, the original role of such a vertical register in a solid-state imaging device is to read out and transfer a signal (charge) received by a photosensitive section. However, an increasing number of devices are designed to sweep out unnecessary charges that cause blooming and the like from the transfer register during the light reception period when the photosensitive section receives light. This is preferable because there is no need to provide an overflow drain region and the degree of integration can be improved.

However, in this case, there is a problem that dark current increases. This problem will be specifically explained with reference to FIG. FIG. 1 is a configuration diagram showing the planar structure of one light-receiving element and its surrounding area.
1 is a light-receiving element (the part inside the satin-finished pattern part), which is composed of, for example, a photodiode formed between the substrate and the substrate by selectively forming an n-type semiconductor region on the surface of the P-type semiconductor substrate. Reference numeral 2 denotes a channel stopper (shown with a matte pattern), which is formed by making the impurity concentration in a rectangular annular region around the light receiving element 1 higher than that of the semiconductor substrate on the surface of the semiconductor substrate. In the channel stopper 2, a part (indicated by diagonal lines) 3 has an impurity concentration lower than the other part, so that the part 3 becomes a read gate part. Reference numeral 4 denotes a vertical register, which is composed of an n-type semiconductor region formed in the middle of adjacent vertical columns of light-receiving elements 1 so as to extend along the vertical transfer direction.

P1-P4 are vertical transfer electrodes formed on the surface of the semiconductor substrate to extend horizontally through an insulating film, and are arranged in the order of Pi, P2, P3, and P4 in the vertical transfer direction. Each of the vertical transfer electrodes P1, P2, P3, and P4 is formed not in a band shape but in a comb-like shape so as not to overlap with the light receiving element l. Also, Pl! 1-P2 and
Although P3 and P4 partially overlap each other, P2 and P4 are in the lower layer, and Pl and P3 are in the upper layer. The electrode P3 partially overlaps with the readout gate section 2.

Figure 2 shows the conventional vertical transfer electrodes P1, P2, P3.
．． 3 is a waveform diagram of signals φl, φ2, φ3, and φ4 applied to P4. FIG.

In this solid-state imaging device, sweeping out unnecessary charges and signal transfer are performed by a four-phase drive blade type, and therefore the signal φl
~φ4 is, for example, +5v during the sweep period and transfer period.
It becomes a lock pulse that can be driven in four phases in the range of -5V. Further, reading of the signal to the vertical register 4 through the read gate section 3 is performed by raising the transfer electrodes P1 and P2 to, for example, +IOV and lowering the transfer electrodes P2 and P4 to -5V. During the light reception period, the vertical register 4 must function as an overdrain in order to quickly sweep out unnecessary charges within the vertical register 4. Therefore, at least the electrodes PL, P3
It is necessary to make the electrodes PI, P
If only P2 and P4 are set to a high level and P2 and P4 are set to a low level, the charge under the part between electrodes Pi and P3 cannot be completely swept out. In order to sweep out the charge more smoothly, it is necessary to set all electrodes Pi, P2, P3, and P4 to the same high level.

Therefore, during the light reception period, all electrodes P1 to P4 are set to +8V, for example.
This is done to raise the level of performance to a high level.

By the way, when all the electrodes P1, P2, P3, and P4 are made high in this way, the channel stopper 2 around the light receiving element 1 enters the depletion mode, and all the interface states of the channel stopper 2 become open. Then, a dark current is generated using the depleted level as a recombination center.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to prevent interface levels existing under an electrode around a light-receiving element from becoming a source of dark current during a light-receiving period.

Structure of the Invention In order to achieve the above object, the driving method of the solid-state imaging device of the present invention uses a vertical register in a time-sharing manner as a transfer register for reading and transferring signals obtained by a light receiving element and as an overflow drain for discharging excess charge. A method for driving a solid-state imaging device, which involves applying a predetermined voltage to a vertical transfer electrode during each light reception period to sweep out unnecessary charges, and bringing the surface of a peripheral region of a light receiving element into an atoning state of majority carriers in the peripheral region. The invention is characterized in that the operation is driven in such a way that the operations of 1 and 2 are alternately repeated with the same period of time as one horizontal period.

Embodiments Below, a method for driving a solid-state imaging device of the present invention will be explained in detail according to embodiments shown in the accompanying drawings.

FIG. 3 shows signals φ1, φ2, φ applied to each transfer electrode in an example of the driving method of the solid-state imaging device of the present invention.
3. This is a time chart of φ4. This transfer electrode Pi,
Signals φ1, φ2, φ3, applied to P2, P3, P4
φ4 differs from the conventional case shown in FIG. 2 only in the waveform during the light reception period. That is, in the solid-state imaging device having the structure shown in FIG.
For example, the voltage of each electrode P1 to P4 governing the readout gate section 3 is set to a voltage Vml (for example, +8V) slightly shallower than the above voltage vh during light reception, and a signal is generated at the light receiving element 1. Accumulation of charge takes place. Also, at that time, the voltage Vm
The generated charge exceeding the potential corresponding to l flows into the vertical register 4 side.

By the way, in the present invention, each vertical transfer electrode P1 during light reception
The state in which ~P4 receives voltage V m 1 is one horizontal period (H
) or more continues from 1 to no more.

That is, in the scanning period of l horizontal period, each vertical transfer electrode P
Although the voltage applied to 1-P4 is set to Vml, each vertical transfer electrode PI-P4 is set to a low level of, for example, -5V during the retrace period, thereby reducing the dark current generated from the channel stopper 2. The reason why the dark current can be reduced by temporarily lowering the vertical transfer electrodes P1 to P4 to a low level is as follows.

That is, by setting the upper electrode to a negative level, the surface of the P-type semiconductor region can be brought into a hole-free or W-joon state. In such an empty state, the interface states are occupied by holes. By the way, if a positive voltage is applied to the electrode to deplete the P-type semiconductor region in such an akime solution state, the holes occupying the interface state will deplete the interface state with a certain time constant. released from. The time constant is a function of the level of the level, and is approximately 10 = s eC near the midgap, which is the center of recombination.

Therefore, by making the time during which a positive voltage is continuously applied to each vertical transfer electrode P1 to P4 shorter than the time constant of the level near the midgap, which is the recombination center, the effective number of recombination centers is reduced. be able to. Therefore, the dark current generated from the channel stopper 2 of the light receiving element 1 can be reduced.

In summary, if the electrodes P1-P4 are kept high for example during the l field, a large amount of dark current will be generated, so that the holes are brought into a state of heaping, for example every horizontal retrace period. Of the dark currents that collect in the light-receiving element l, the ratio of that generated within the light-receiving element l itself to that generated around it is 171 N1. : 10, the driving method of the present invention reduces the dark current by 0.5 to 0.
It can be reduced to 1.

FIG. 4 shows that each electrode Pi-P4 is set to a low level during the light reception period, that is, during the horizontal scanning (trace) period, and is set to a high level only during the horizontal retrace period;
That is, this shows an embodiment that is opposite to the case shown in FIG. The present invention can also be implemented in such an embodiment.

Effects of the Invention As described above, the method for driving the solid-state imaging device of the present invention!
± is a driving method for a solid-state imaging device in which a vertical register is used time-divisionally as a transfer register for reading and transferring signals obtained by a light-receiving element and as an overflow drain for discharging surplus charge, in which a vertical transfer register is used in each light-receiving period. The operation of applying a predetermined voltage to a state where unnecessary charges are swept out and the operation of bringing the surface of the peripheral area of the light receiving element into a state of acquisition of majority carriers in that peripheral area are alternated with a period equal to one horizontal period. It is characterized by being driven repeatedly.

Therefore, according to the present invention, during the light receiving period, the state in which unnecessary charges are swept out does not continue for a time longer than the time constant at which majority carriers are released when the peripheral region of the light receiving element is depleted, and Since the surface of the peripheral region of the light-receiving element is brought into a state of ablation of majority carriers in the peripheral region once every period, the number of effective recombination centers that cause dark current can be reduced. Therefore, according to the present invention, dark current can be reduced.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing a light receiving element and its surroundings in an example of a solid-state imaging device, Fig. 2 is a time chart of signals applied to each vertical transfer electrode to explain a conventional driving method, and Figs. FIG. 4 is a time chart of signals applied to each vertical transfer electrode for explaining different embodiments of the driving method of the present invention. Explanation of symbols 1 -- Light-receiving element, 211 -- Peripheral area of light-receiving element, 4
・・・Vertical register, p1-P4・0・Vertical transfer electrode Applicant: Sony Corporation Representative Patent Attorney Haruto Komatsu Hideo Ogawa 2

Claims (1)

[Claims] (1) A driving method for a solid-state imaging device in which a vertical register is used time-divisionally as a transfer register for reading and transferring signals obtained by a light receiving element and as an overflow drain for sweeping out excess charge, in which vertical registers are transferred during each light receiving period. The operation of applying a predetermined voltage to the electrode to sweep out unnecessary charges and the operation of bringing the peripheral surface of the light-receiving element into a state of accumulation of majority carriers in the peripheral area are alternately repeated with a period equal to one horizontal period. A method for driving a solid-state imaging device, characterized in that the device is driven so as to