JP4465309B2 - CCD type solid-state imaging device and transfer control method thereof - Google Patents

Description

  The present invention relates to a CCD (Charge Coupled Device) type solid-state imaging device, and more particularly to a CCD type solid-state imaging device capable of reducing dark current contained in signal charges and a transfer control method thereof.

  The CCD type solid-state imaging device, for example, as described in Patent Document 1 below, transfers the received light charges (signal charges) read from the photodiodes in the first direction (hereinafter referred to as the vertical direction). And a horizontal transfer path (HCCD) that receives the received charge transferred by the vertical transfer path and transfers it in a second direction (hereinafter referred to as a horizontal direction).

  FIG. 4 is a schematic diagram of the surface of a general CCD solid-state imaging device. A large number of photodiodes 1 (PD1 to PD8) are arranged in a square lattice pattern on the semiconductor substrate of the CCD type solid-state imaging device of the example shown in the drawing, and the vertical transfer path 2 along each column of the photodiodes 1 is formed. Is formed.

  Each vertical transfer path 2 includes two vertical transfer electrodes for one photodiode 1. In the example shown in the drawing, the vertical transfer electrode on the upper side in the vertical direction and the photodiode 1 are connected by a read gate 3. The light-receiving charge of the diode 1 is read through the read gate 3 into a potential packet formed under the corresponding vertical transfer electrode.

  Since the CCD type solid-state imaging device illustrated in FIG. 4 is driven in eight phases, V1, V2,..., V8 are described in each vertical transfer electrode, and the vertical transfer control unit 8 is provided in each transfer electrode V1 to V8. Supplies transfer pulses φV1 to φV8, thereby performing vertical transfer control.

  A horizontal transfer path 4 is provided on the lower side of the semiconductor substrate. The photoreceived charges transferred in the vertical direction by the vertical transfer paths 2 are received, and the received charges are then transferred in the horizontal direction. Through this, an image signal corresponding to the amount of received light charge is output.

  5 and 6 are timing charts showing a conventional transfer control method. When the vertical transfer control unit applies the transfer pulses φV1 to φV8 shown in FIG. 6 to the vertical transfer electrodes V1 to V8, the signal charges are changed. As shown in FIG. 5, the data is transferred along the vertical transfer path.

  For example, at time t4, the signal charge read from the photodiode 1 is stored in a six-electrode width potential packet formed under the electrodes V4, V5, V6, V7, V8, and V1, and the next time. At t5, the transfer potential of the electrode V4 is changed from a high level (for example, 0V) to a low level (for example, −8V), so that the potential packet width is narrowed to 5 electrodes of V5, V6, V7, V8, and V1, At the next time t6, the transfer potential of the electrode V2 on the transfer direction side is changed from a low level to a high level, so that the potential packet width is expanded to six electrodes V5, V6, V7, V8, V1, and V2. .. Are repeated, and signal charges are transferred in the vertical direction.

  In this way, the signal charge transferred to the end of the vertical transfer path is now transferred to the horizontal transfer path. Then, the data is transferred along the horizontal transfer path, but the operation of the vertical transfer path must be stopped while the horizontal transfer path is transferring signal charges.

  The time s1 shown in FIGS. 5 and 6 is a time indicating that transfer is being performed by the horizontal transfer path, and is also a standby time for stopping the vertical transfer path. During the waiting time s1, the signal charge on the vertical transfer path is held on the vertical transfer path and is not moved. In the conventional example shown in the figure, during the standby time s1, the transfer potential applied to the electrodes V1 and V8 is maintained at a low level to form a barrier so as not to be mixed with the signal charge of the adjacent potential packet. Then, by maintaining the electrodes V2 to V7 at a high level, a potential packet having a width of 6 electrodes is formed under the electrodes V2 to V7, and signal charges are held therein.

Japanese Unexamined Patent Publication No. 2000-196066

  When imaging an image with a CCD type solid-state imaging device, the light-receiving charge of each photodiode is read out to the vertical transfer path and transferred in the order of the vertical transfer path and horizontal transfer path to output the image signal from the solid-state image pickup apparatus. High-quality image data cannot be obtained unless the charge other than the light-receiving charge is prevented from being mixed into this charge.

  Even when the photodiode is not receiving light, for example, a charge is generated by thermal excitation. When this charge, that is, a dark current, is mixed into the signal charge in the potential packet during the standby time s1, image quality deterioration occurs. In order to obtain high-quality image data, it is necessary to reduce the dark current mixed in the waiting signal charges.

  An object of the present invention is to provide a CCD type solid-state imaging device and a transfer control method thereof that can reduce dark current mixed in signal charges waiting on a vertical transfer path.

The CCD solid-state imaging device and the transfer control method thereof according to the present invention are a plurality of two-dimensionally arrayed semiconductor substrates on which even-numbered photodiodes are arranged with a 1/2 pitch shift from odd-numbered photodiodes. A photodiode, a vertical transfer path for reading the received charge of the photodiode through the gate and transferring it in the vertical direction, a horizontal transfer path for transferring the received charge received from the vertical transfer path in the horizontal direction, and the vertical A potential packet is formed under a plurality of continuous transfer electrodes constituting the transfer path, the potential packet is advanced in the vertical direction while expanding and contracting the vertical width of the potential packet, and the received charge is transferred. In the CCD solid-state imaging device, comprising: a transfer control unit that stops the transfer operation of the vertical transfer path during transfer of the horizontal transfer path; , Said maintaining the width of the potential packets to "contraction" state of the stretch, the number of the gate connected to the potential packet in the vertical transfer path of every other row when stopping the transfer operation of the vertical transfer paths The number of the gates connected to the potential packets on the remaining vertical transfer paths every other column is the same .

  The CCD type solid-state imaging device and the transfer control method thereof according to the present invention include first and second transfer electrodes for one photodiode, and the first transfer electrode and the photodiode are the gate. In the above-described CCD type solid-state imaging device to be connected, the vertical transfer path is driven in eight phases, the potential packet is alternately transferred in two states of 6 electrode width and 5 electrode width, and the transfer is performed. When the transfer operation is stopped, the width of the potential packet is maintained at a width of 5 electrodes.

  According to the present invention, it is possible to reduce the number of potential packets that hold a waiting signal charge connected to the readout gate of the photodiode, thereby reducing the dark current mixed in the signal charge, A high-quality image can be taken.

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

(First embodiment)
1 and 2 are timing charts showing a transfer control method of the CCD type solid-state imaging device according to the first embodiment of the present invention. The CCD type solid-state imaging device according to this embodiment is the same as that illustrated in FIG. 4, and the vertical transfer control unit 8 generates transfer pulses φV1 to φV8 shown in FIG. 2 and supplies them to the transfer electrodes V1 to V8.

  In the present embodiment, as in the prior art, for example, at time t5, signal charges are stored in a potential packet having a width of 6 electrodes formed under the electrodes V4, V5, V6, V7, V8, and V1, At time t6, the transfer potential of the electrode V4 is changed from a high level (for example, 0V) to a low level (for example, -8V), so that the potential packet width is narrowed to five electrodes V5, V6, V7, V8, and V1. At the next time t7, the potential packet width is expanded to six electrodes V5, V6, V7, V8, V1, and V2 by changing the transfer potential of the electrode V2 on the transfer direction side from the low level to the high level. ,... Are repeated, and signal charges are transferred in the vertical direction.

  At time t15, signal charges are stored in a potential packet having a width of 6 electrodes under the electrodes V1 to V6, and immediately before the waiting time s1 after the potentials of the electrodes V7 and V8 are lowered to form a barrier. At time 16, the transfer potential of the electrode V1 is changed from a high level (for example, 0V) to a low level (for example, -8V).

  As a result, in this embodiment, the potential packet that holds the signal charge during the standby time s1 has a width of five electrodes below the electrodes V2 to V6, and the transfer potentials of the electrodes V7, V8, and V1 are maintained at a low level. That is, in the present embodiment, the barrier that defines the potential packet has a width of three electrodes.

  1 is different from the prior art shown in FIG. 5 in that the transfer potential applied to the electrode V7 is set to a low level (high level in the prior art of FIG. 5) during the standby time s1. That is, in this embodiment, the potential packet width for holding the signal charge during standby is set to five electrodes, and the potential packet is reduced by one electrode width as compared with the case of waiting with the potential packet for six conventional electrodes. .

  As described above, in the CCD type solid-state imaging device shown in FIG. 4, the electrodes connected to the readout gate 3 are V1, V3, V5, V7, and the electrodes V2, V4, V6, V8 are connected to the readout gate 3. Not. In the present embodiment, the electrode used when the potential packet width during standby is reduced from the conventional 6 electrode width to the 5 electrode width is V7, which is an electrode connected to the read gate.

  For this reason, in this embodiment, the number of read gates connected to the potential packet is reduced from the conventional three (electrodes V3, V5, V7) by setting the potential packet for holding the signal charge during standby to a width of 5 electrodes. The number can be reduced to two (electrodes V3 and V5), and the dark current mixed in the signal charge can be reduced.

(Second Embodiment)
FIG. 3 is a schematic view of the surface of a CCD solid-state imaging device according to the second embodiment of the present invention. Whereas the CCD solid-state imaging device of the first embodiment has photodiodes arranged in a square lattice pattern on a semiconductor substrate, this embodiment is characterized in that the photodiodes are arranged in a so-called honeycomb pattern. Yes.

  That is, the CCD solid-state imaging device 10 of this embodiment includes a light receiving element group in which a light receiving element 11b in which a blue filter is stacked and a light receiving element 11r in which a red filter is stacked are alternately arranged in a horizontal row, and a green filter. Are stacked alternately in the vertical direction with a 1/2 pitch shift from the light receiving element group in which the light receiving elements 11g are stacked in a horizontal row.

  In the drawing, the light receiving elements 11r, 11g, and 11b are displayed as squares inclined by 45 degrees. In the solid-state imaging device 10, transfer electrodes are provided along the sides of the squares of the light receiving elements 11r, 11g, and 11b. The horizontal row V1 of these transfer electrodes is divided by channel stops corresponding to each light receiving element, but the same transfer potential φV1 is applied to the horizontal row of electrode groups V1 at the same timing.

  Since the CCD type solid-state imaging device 10 of the present embodiment is driven in eight phases, each horizontal row of electrode groups repeats..., V7, V8, V1, V2, V3, V4, V5, V6,. The electrode group 101 is connected to the electrode group V1, the electrode terminal 102 is connected to the electrode group V2, the electrode terminal 103 is connected to the electrode group V3,..., And the electrode terminal 108 is connected to the electrode group V8. Connected (that is, the electrode group Vx is connected to the electrode terminal 10x).

  The transfer electrodes 12 provided around the respective light receiving elements 11r, 11g, and 11b are also aligned in the vertical direction, and the transfer electrode group 13 (only one line is shown by a dotted line) arranged in the vertical direction constitutes the vertical transfer path 13. .

  When a readout potential (readout pulse) is applied to a readout gate (not shown) in order to read out an image signal captured by the CCD solid-state imaging device 10 (light-receiving charges of the light-receiving elements 11r, 11g, and 11b), the light-receiving elements 11r and 11g , 11b is read out to the transfer electrode 12 at the tip of the arrow directed diagonally to the lower left illustrated on each light receiving element 11r, 11g, 11b.

  By applying transfer potentials (transfer pulses) φV1 to φV8 to the electrode terminals 101 to 108, the received light charges are transferred in the vertical direction, and then the received light charges are transferred and transferred to the horizontal transfer path 14 for output. It is output as an image signal from the amplifier 15.

  The timing chart for performing the transfer control in the CCD type solid-state imaging device 10 is the same as that shown in FIGS. Also in this embodiment, during the standby time s1, the transfer potentials of the electrodes V7, V8, and V1 are maintained at a low level (for example, −8V) as a barrier, and the transfer potentials of the electrodes V2 to V6 are set to a high level (for example, 0V). The potential packet for holding the signal charge is formed.

  Thereby, the number of read gates connected to the potential packet during the standby time s1 is reduced, and the dark current mixed in the signal charge can be reduced.

  When the conventional transfer control shown in FIG. 5 (transfer control using the electrodes V1 and V8 as a barrier during the standby time s1) is applied to the CCD solid-state imaging device 10 of FIG. 3, the red light receiving elements in the rightmost column of FIG. In a column in which (photodiode) 11r and blue light receiving element 11b are alternately arranged in the vertical direction (this is referred to as column A), the potential packet and the readout gate are connected at one point of electrode V5, and the adjacent green light receiving unit is received. In a column in which the elements 11g are arranged in the vertical direction (this is referred to as a B column), the potential packet and the readout gate are connected at two positions of the electrodes V3 and V7.

  On the other hand, in the transfer control of this embodiment (transfer control using the electrodes V1, V8, and V7 as a barrier during the standby time s1), in the A column, the potential packet and the readout gate are connected at one place of the electrode V5. In the B column, the potential packet and the readout gate are connected at one position of the electrode V3.

  That is, as a whole, the potential packet is conventionally connected to the read gate at three locations, whereas in the present embodiment, it is connected at two locations, so that the total dark current mixed in the signal charge is reduced.

  Further, in the present embodiment, the number of readout gates connected to the potential packet during standby is one in the A column (electrode V5) and two in the B column (V3, V7). The number of locations where dark current flows is the same in rows A and B, and the number of locations where dark current flows is the same in rows A and B. Even in a CCD type solid-state imaging device with a honeycomb arrangement, higher image quality is achieved than in the past. It becomes possible.

  The CCD solid-state imaging device according to the present invention can reduce the dark current mixed in the waiting signal charge, and is useful as a CCD solid-state imaging device mounted on a digital camera that captures high-quality images and a transfer control method. .

It is transfer explanatory drawing of the CCD type solid-state imaging device which concerns on the 1st Embodiment of this invention. It is a timing chart of the transfer pulse which performs the transfer shown in FIG. It is a surface schematic diagram of the CCD type solid-state imaging device concerning a 2nd embodiment of the present invention. It is a surface schematic diagram of a general CCD type solid-state imaging device in which photodiodes are arranged in a square lattice pattern. It is a figure explaining the mode of transfer in the conventional vertical transfer path. 6 is a timing chart of transfer pulses for performing the transfer shown in FIG. 5.

Explanation of symbols

1, 11r, 11g, 11b Light receiving element (photodiodes PD1 to PD8)
2,13 Vertical transfer path 3 Read gates 4, 14 Horizontal transfer paths 5, 15 Output amplifier 8 Vertical transfer control units V1-V8 Transfer electrodes φV1-φV8 Transfer potential s1 Vertical transfer path standby time (during horizontal transfer path transfer) time)

Claims (4)

A plurality of photodiodes that are two-dimensionally arranged on a semiconductor substrate and in which even-numbered photodiodes are shifted by 1/2 pitch with respect to odd-numbered photodiodes, and received light charges of the photodiodes via gates A vertical transfer path for reading and transferring in the vertical direction, a horizontal transfer path for transferring the received light charges received from the vertical transfer path in the horizontal direction, and a potential under a plurality of continuous transfer electrodes constituting the vertical transfer path. A packet is formed, the potential packet is advanced in the vertical direction while expanding and contracting the width of the potential packet in the vertical direction, the received light charges are transferred, and the transfer operation of the vertical transfer path is performed during the transfer of the horizontal transfer path. In the CCD type solid-state imaging device including the transfer control unit to be stopped, the transfer control unit is configured to stop the transfer operation of the vertical transfer path. Maintaining the width of the packet to "contraction" state of the telescopic connection to the potential packet in the vertical transfer path of every number and the remaining one column of said gate connected to said potential packet in the vertical transfer path of every other row A CCD type solid-state imaging device, comprising means for making the number of gates equal to each other .   2. The CCD solid-state imaging device according to claim 1, wherein the first transfer electrode and the photodiode are connected by the gate, the first and second transfer electrodes being provided for one photodiode. When the transfer control unit drives the vertical transfer path for eight phases, performs the transfer by alternately realizing the two states of the six-electrode width and the five-electrode width, and stops the transfer operation. A CCD type solid-state imaging device, wherein the potential packet is maintained at a width of 5 electrodes. A plurality of photodiodes that are two-dimensionally arranged on a semiconductor substrate and in which even-numbered photodiodes are shifted by 1/2 pitch with respect to odd-numbered photodiodes, and received light charges of the photodiodes via gates A vertical transfer path for reading and transferring in the vertical direction, a horizontal transfer path for transferring the received light charges received from the vertical transfer path in the horizontal direction, and a potential under a plurality of continuous transfer electrodes constituting the vertical transfer path. A packet is formed, the potential packet is advanced in the vertical direction while expanding and contracting the width of the potential packet in the vertical direction, the received light charges are transferred, and the transfer operation of the vertical transfer path is performed during the transfer of the horizontal transfer path. In the transfer control method for a CCD solid-state imaging device comprising a transfer control unit to be stopped, the transfer control unit stops the transfer operation of the vertical transfer path. The width of the potential packet is maintained in the contracted “contracted” state, and the number of the gates connected to the potential packet on every other vertical transfer path and the rest on every other vertical transfer path A transfer control method for a CCD type solid-state imaging device, wherein the number of gates connected to a potential packet is the same . 4. The transfer of a CCD solid-state imaging device according to claim 3, further comprising a first transfer electrode and a second transfer electrode for each of the photodiodes, wherein the first transfer electrode and the photodiode are connected by the gate. In the control method, when the vertical transfer path is driven in eight phases, the potential packet is alternately transferred to two states of 6 electrode width and 5 electrode width, the transfer is performed, and the transfer operation is stopped when the transfer operation is stopped. A transfer control method for a CCD solid-state imaging device, wherein the packet width is maintained at a width of 5 electrodes .

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