JPH0219675B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a two-dimensional solid-state imaging device.

FIG. 1 is a schematic plan view of a conventional two-dimensional solid-state imaging device. In the figure, a large number of storage regions 1 are formed in a plurality of rows on the light-receiving side main surface of a semiconductor substrate and are connected to the substrate in pn junction and accumulate signal charges caused by incident light. A vertical signal line 2 is provided corresponding to each column of storage region 1 . A vertical switch 3 of a MOS field effect transistor (MOSFET) is located between the storage region 1 and the vertical signal line 2, and controls the movement of signal charges from the storage region 1 to the vertical signal line. These vertical switches 3 are driven by a vertical shift register 4. An embedded charge coupled device 5 is provided corresponding to one end of the vertical signal line 2 . As the horizontal charge transfer device, a buried charge coupled device (BCCD), a surface charge coupled device (SCCD), or a bucket brigade device (BBD) can be used. BCCD is suitable because it has good signal charge transfer efficiency. At least one transfer stage of the embedded charge coupled device 5 corresponds to one vertical signal line. Between the vertical signal line 2 and the embedded charge-coupled device 5, there is a connection between the vertical signal line 2 and the embedded charge-coupled device 5.
A horizontal switch 6 is provided to control the movement of signal charges to. This horizontal switch 6 is composed of one or more MOSFETs. Figure 1 shows the case where one MOSFET is used. One end of the embedded charge-coupled device 5 is connected to an output device 7
It is connected to the.

The two-dimensional solid-state imaging device shown in FIG. An imaging operation is performed in which the signal is transferred to the charge-coupled device 5, and further sent to the output device 7 by transfer from the embedded charge-coupled device 5, and taken out as an output signal.

However, since the capacitance of the vertical signal line 2 is about 5 pF, which is very large, the transfer efficiency of signal charges from the vertical signal line 2 to the embedded charge-coupled device 5 is not good. The transfer efficiency was particularly poor when the incident light was small and the signal charge was small, and the picture on the playback screen ran vertically, making it unsightly. In addition, attempts have been made to utilize bias light in order to improve transfer efficiency, but this method has the disadvantage that it is difficult to uniformly irradiate each storage region with bias light.

The purpose of this invention is to eliminate the above-mentioned drawbacks,
An object of the present invention is to provide a method for driving a two-dimensional solid-state imaging device that can obtain good reproduced images.

According to the present invention, a large number of accumulation regions are arranged in a plurality of columns for accumulating signal charges caused by incident light, a vertical signal line is provided corresponding to the column of the accumulation region, and the accumulation region and the vertical signal line are arranged in a plurality of columns. a vertical switch provided between the vertical signal line and the embedded horizontal charge coupling device for charge readout provided corresponding to one end of the vertical signal line; A method for driving a two-dimensional solid-state imaging device, comprising: a horizontal switch provided between the device and the vertical signal line; and a surface-type horizontal charge coupling device for injecting a bias charge corresponding to the other end of the vertical signal line. During the horizontal retrace period, the channel potential of the surface-type horizontal charge coupling device is made shallower than the potential of the vertical signal line, and the bias charge stored in the surface-type horizontal charge coupling device is completely transferred to the vertical signal line. Driving a two-dimensional solid-state imaging device, further comprising transferring the signal charge transferred from the accumulation region to the vertical signal line and the bias charge from the vertical signal line to the embedded horizontal charge coupling device. method is obtained.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic plan view of a two-dimensional solid-state imaging device according to an embodiment of the present invention. Figures 1 and 2
In the figures, the same symbols indicate the same components. In this device, a surface type horizontal charge coupling device 8 for injecting bias charges into the vertical signal line 2 is provided corresponding to the other end of the vertical signal line 2 . 1
At least one transfer stage of the horizontal charge coupling device 8 corresponds to the vertical signal line of the book.
In this embodiment, one transfer stage corresponds. An input device 9 is provided at one end of the surface charge coupled device 8 for injecting a bias charge into the surface charge coupled device 8. A transfer gate 10 is provided between the vertical signal line 2 and the surface-type charge-coupled device 8 to control the transfer of bias charges from the surface-type charge-coupled device 8 to the vertical signal line 2 . This 2
In the dimensional solid-state imaging device, a certain amount of bias charge is injected from the input device 9 into the surface-type charge-coupled device 8 . While signal charges are being transferred by the embedded charge coupled device 5, bias charges are transferred by the surface charge coupled device 8 in synchronization with this operation. When all the signal charges corresponding to one horizontal scanning line are transferred to the output device 7 by the embedded charge coupling device 5, the signal charges are transferred to the transfer stage of the surface charge coupling device 8 corresponding to all the vertical signal lines 2. A certain amount of bias charge is stored. During the horizontal retrace period, this bias charge is transferred to transfer gate 1.
0 to the vertical signal line 2. This transfer is a complete transfer, and each transfer stage of the surface charge coupled device 8 is completely depleted. Furthermore, the signal charge due to the incident light accumulated in the accumulation region 1 is transferred to the vertical switch 3.
The signal charges and bias charges are transferred to the embedded charge coupling device 5 via the horizontal switch 6.

In an embodiment according to the invention, a certain amount of bias charge is supplied from one input section 9 to the surface charge coupled device 8.
Since this bias charge is completely transferred from each transfer stage of the surface-type charge coupled device 8 to the corresponding vertical signal line 2, the variation in the amount of bias charge transferred to each vertical signal line 2 is very large. small.

In the embodiment of the present invention described above, the bias charge is transferred to the vertical signal line before the signal charge, but the reverse order may be used.

In order to completely transfer the bias charge from the surface-type charge-coupled device 8 to the vertical signal line 2, the bias potential of the vertical signal line 2 is made larger than the off-level channel potential of the surface-type charge-coupled device 8. There must be. In order to reduce the bias potential of the vertical signal line 2, it is advantageous to use an SCCD, which has a lower channel potential than a BCCD, as a horizontal charge coupling device. SCCDs have lower transfer efficiency than BCCDs, but transfer efficiency is irrelevant because a fixed amount of bias charge is transferred.

In order to increase the transfer efficiency of signal charge transfer from the vertical signal line to the embedded charge coupled device, a priming transfer method has been proposed. In this priming transfer method,
The horizontal switch consists of two MOSFETs and one capacitor, and internally generates and absorbs bias charges. Also in this priming transfer method, if bias charges are externally injected and output together with signal charges, the transfer efficiency is increased. When the method according to the present invention is used in combination with the priming water transfer method, the transfer efficiency is further improved.

When the amount of incident light is large and a charge larger than the maximum amount of accumulated charge in the accumulation region is generated, the charge flows out from the accumulation region to the vertical signal line, and this outflow charge is mixed with signal charges in other accumulation regions. It appears as a white line on the playback screen and deteriorates the image quality.
This phenomenon is called blooming phenomenon. In order to prevent the blooming phenomenon, a charge absorption part is provided corresponding to the vertical signal line, and a control gate is provided between the vertical signal line and the charge absorption part to control the transfer of charge from the vertical signal line to the charge absorption part. 2
A dimensional solid-state imaging device has been proposed. In this two-dimensional solid-state imaging device, during the horizontal retrace period, the charge flowing out to the vertical signal line is transferred to the charge absorption section via the control gate and absorbed by the charge absorption section, and then the signal is sent from the storage region to the vertical signal line. Charge is transferred and the signal charge is transferred from the vertical signal line to the embedded charge coupled device via the horizontal switch. Therefore, the blooming phenomenon is prevented because the leaked charges are not mixed into the signal charges. At this time, it is desired that the transfer efficiency is high when transferring the leaked charges from the vertical signal line to the charge absorption section. The method according to the present invention allows high transfer efficiency to be achieved using bias charges. Note that the charge absorption section and the control gate are provided adjacent to the embedded charge-coupled device and on the opposite side of the horizontal switch, and the charge that flows out is transferred through the horizontal switch, one transfer stage of the embedded charge-coupled device, and the control gate. Of course, it can also be applied to a two-dimensional solid-state imaging device in which charge is transferred from a vertical signal line to a charge absorption section.

A bias charge may be necessary for both the transfer of outflow charge from the vertical signal line to the charge absorption section and the transfer of signal charge from the vertical signal line to the embedded charge-coupled device. In this way, when bias charges are required multiple times in one horizontal retrace period, multiple transfer stages of the surface-type charge coupling device may be associated with one vertical signal line. or
A plurality of surface charge coupled devices may be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of a conventional two-dimensional solid-state imaging device, and FIG. 2 is a schematic plan view of a two-dimensional solid-state imaging device according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Storage region, 2...Vertical signal line, 3...Vertical switch, 5...Embedded charge coupled device, 6
...Horizontal switch, 8...Surface type charge coupled device.

Claims (1)

[Claims] 1. A large number of accumulation regions arranged in multiple columns for accumulating signal charges caused by incident light, vertical signal lines provided corresponding to the columns of the accumulation regions, and between the accumulation regions and the vertical signal lines. a vertical switch provided, an embedded horizontal charge coupling device for reading charge provided corresponding to one end of the vertical signal line, and between the vertical signal line and the embedded horizontal charge coupling device; A method for driving a two-dimensional solid-state imaging device comprising: a horizontal switch provided at the horizontal switch; and a surface-type horizontal charge coupling device for injecting a bias charge corresponding to the other end of the vertical signal line, the method comprising: During the retrace period, the channel potential of the surface-type horizontal charge-coupled device is made shallower than the potential of the vertical signal line, and the bias charge stored in the surface-type horizontal charge-coupled device is completely transferred to the vertical signal line, and further, A method for driving a two-dimensional solid-state imaging device, characterized in that the signal charge and the bias charge transferred from the accumulation region to the vertical signal line are transferred from the vertical signal line to the embedded horizontal charge coupling device.