JP4225989B2 - Solid-state image sensor - Google Patents

Description

  The present invention includes a large number of photoelectric conversion elements arranged in a row direction and a column direction perpendicular thereto, a first transfer unit that transfers charges read from the large number of photoelectric conversion elements in the column direction, The present invention relates to a solid-state imaging device having an output unit that outputs a signal corresponding to the charge transferred from a second transfer unit.

  A CCD type solid-state imaging device mounted on a digital camera or the like usually includes a VCCD (vertical charge transfer device) and an HCCD (horizontal charge transfer device). In an interline CCD solid-state imaging device, a large number of photoelectric conversion elements are arranged in a matrix along a plurality of rows and columns, and one VCCD is arranged in each photoelectric conversion element column. In many CCD type solid-state imaging devices, each VCCD is electrically connected to one HCCD.

  The VCCD is generally constituted by a charge coupled device (CCD) in which the concentration of the n-type impurity in the n-type channel is substantially constant and the thickness of the electrical insulating film on the n-type channel is also substantially constant. This charge coupled device is usually driven by vertical drive signals of three or more phases. In each VCCD, one vertical charge transfer stage is constituted by one electrode and a region of the n-type channel located under this electrode. Generally, about 2 to 4 vertical charge transfer stages are arranged for one photoelectric conversion element.

  In order to increase the transfer efficiency of the VCCD, conventionally, the driving method is set to eight-phase driving or the like to cope with reliable transfer of charges and complicated charge reading patterns from the photoelectric conversion elements. However, in order to support the multi-phase driving method, it is necessary to form many vertical charge transfer stages for one photoelectric conversion element, and accordingly, it is necessary to increase the number of electrodes. Increasing the number of electrodes in solid-state imaging devices that are becoming increasingly miniaturized in this way means that it is necessary to form finer electrodes, resulting in problems such as an increase in the number of manufacturing processes and a decrease in production yield. It becomes.

  Therefore, conventionally, in order to improve the charge transfer efficiency of the VCCD, an element in which a potential slope is formed by providing a concentration gradient or the like in an n-type channel included in each vertical charge transfer stage has been proposed (Patent Document 1, Patent Document 1). 2).

Japanese Patent Laid-Open No. 9-223787 JP-A-7-74344

  When the potential slope is formed as in Patent Documents 1 and 2, it is possible to improve the charge transfer efficiency. However, for example, in the case of 8-phase driving, there are still 8 terminals for supplying the vertical driving signal to the electrodes. , That number can not be reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid-state imaging device capable of reducing the number of terminals while improving the charge transfer efficiency of the VCCD.

The solid-state imaging device according to the present invention includes a large number of photoelectric conversion elements arranged in a row direction and a column direction orthogonal thereto, and a first transfer that transfers charges read from the large number of photoelectric conversion elements in the column direction. Unit, a second transfer unit that transfers the charge transferred from the first transfer unit in the row direction, and an output unit that outputs a signal corresponding to the charge transferred from the second transfer unit The first transfer unit, which is a solid-state imaging device and includes a plurality of transfer stages, is four-phase driven by drive signals φV1, φV2, φV3, and φV4, and each of the transfer stages is adjacent to the charge transfer direction. The two drive electrodes to which one of the drive signals is supplied and a channel region formed below the drive electrode are arranged, and the channel region extends over the entire first transfer unit. The impurity concentration is constant, One of the driving electrodes is set higher than the potential of the drive electrode potential of the driving electrodes located on the upstream side of the transfer direction of charge is located on the downstream side,
Two of the transfer stages are connected to one of the photoelectric conversion elements, and the drive electrodes are connected to the drive electrodes of a total of four transfer stages connected to the two photoelectric conversion elements arranged adjacent in the column direction. When the signals φV1, φV2, φV3, and φV4 are supplied and charges are transferred by the first transfer unit, the potentials of the channel regions of the four transfer stages become deeper from upstream to downstream in the transfer direction. ing.

Solid-state imaging device of the invention, the potential of the drive electrode is inclined to become lower toward the downstream from the upstream of the transfer direction.

  According to the present invention, it is possible to provide a solid-state imaging device capable of reducing the number of terminals while improving the charge transfer efficiency of the VCCD.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing a schematic configuration of a solid-state imaging device for explaining an embodiment of the present invention.
A solid-state imaging device 200 illustrated in FIG. 1 includes a large number of photoelectric conversion elements 10 arranged in a row direction on an n-type silicon substrate 100 and a column direction orthogonal thereto, and a charge readout region from each of the large number of photoelectric conversion elements 10. A first transfer unit 20 that transfers the charges read out via 60 in the column direction, a second transfer unit 40 that transfers the charges transferred from the first transfer unit 20 in the row direction, and a second transfer unit And an output unit 50 that outputs a signal corresponding to the electric charge transferred from 40. In the present specification, the movement of the charges transferred by the first transfer unit 20 is regarded as one flow, and the relative positions of the individual members and the like are set to “any upstream”, “ It is specified as “what downstream”.

FIG. 2 is a partially enlarged view schematically showing a schematic configuration of the first transfer unit 20 shown in FIG.
The first transfer unit 20 includes an n-type channel 20a having a substantially constant n-type impurity concentration, and drive electrodes V1 to V8 made of polysilicon or the like formed on the n-type channel 20a via an electrical insulating film. Composed. In the first transfer unit 20, one transfer stage is configured by two adjacent drive electrodes and a region of the n-type channel 20a formed therebelow. In the example of FIG. 2, the transfer stages are constituted by the drive electrodes V1 and V2, the drive electrodes V3 and V4, the drive electrodes V5 and V6, and the drive electrodes V7 and V8, respectively, and two transfer stages for one photoelectric conversion element 10. Is provided.

  The potential of each of the two drive electrodes constituting one transfer stage is such that the drive electrodes (V2, V4, V6, V8) located upstream in the transfer direction of the first transfer unit 20 are transferred by the first transfer unit 20. It is higher than the drive electrodes (V1, V3, V5, V7) located downstream in the direction. This can be realized by adjusting the dose amount of ions when forming the drive electrode. For example, the drive electrodes (V1, V3, V5, V8) may be formed with a larger dose than the drive electrodes (V1, V3, V5, V7).

  The same drive signal is supplied to the two drive electrodes constituting one transfer stage. In the solid-state imaging device 200 of the present embodiment, a drive signal φV1 is supplied to the drive electrodes V1 and V2, a drive signal φV2 is supplied to the drive electrodes V3 and V4, and a drive signal φV3 is supplied to the drive electrodes V5 and V6. The drive signal VV4 is supplied to the drive electrodes V7 and V8, whereby the first transfer unit 20 is driven in four phases.

  The potential of the n-type channel 20a included in one transfer stage during the transfer operation of the first transfer unit 20, that is, when the drive signals φV1 to φV4 are supplied depends on the difference in potential between the two drive electrodes. The downstream side in the transfer direction is deeper than the upstream side. For this reason, in one transfer stage, in addition to charge movement due to self-induced drift and diffusion, movement due to fringe electric field drift also occurs, and the charge easily flows from upstream to downstream in the transfer direction. improves.

  FIG. 3 is a diagram illustrating a potential flow of the n-type channel 20a during the transfer operation of the first transfer unit of the solid-state imaging device according to the present embodiment. In the figure, hatching indicates electric charge, and symbols V1 to V8 indicate drive electrodes. As shown in FIG. 3, a step-like potential descending in a deep direction from upstream to downstream in the transfer direction is formed under the two electrodes constituting one transfer stage, and the drive signals φV1 to φV4 are sequentially switched. The charge is transferred in the transfer direction.

  As described above, according to the solid-state imaging device 200 of the present embodiment, since the transfer stage is configured by combining two electrodes having different potentials, the charge transfer efficiency during charge transfer can be improved. High-speed driving is possible. In addition, since this efficient charge transfer can be performed by four-phase driving while securing a transfer capacity equivalent to that in the case of eight-phase driving, the number of terminals for supplying drive signals is eight-phase driving. The advantage is that it can be halved. In addition, the configuration of this embodiment is easier to manufacture than the conventional method in which a concentration gradient is provided in the n-type channel or the potential slope is formed by changing the thickness of the insulating film under the drive electrode stepwise. Therefore, manufacturing cost can be suppressed. In addition, according to the present embodiment, since high-speed driving is possible, when performing pixel mixture reading used in the moving image mode or the like, the number of pixel mixtures is increased without increasing the transfer period in the first transfer unit 20. There is also an advantage that can be done.

  In the above description, the configuration in which the photoelectric conversion elements are arranged in a square lattice shape is taken as an example. However, as shown in FIG. 4, a large number of photoelectric conversion elements 10 ′ are arranged in the row direction and the column direction orthogonal thereto. A large number of photoelectric conversion element rows composed of the photoelectric conversion elements 10 ′ arranged in the row direction are divided into approximately half of the arrangement pitch of the photoelectric conversion elements 10 ′ in the row direction by the odd and even rows. The present invention can be applied even to a so-called honeycomb arrangement in which the arrangement is shifted from each other only in the row direction. In the case of the configuration shown in FIG. 4, the drive electrodes V1 and V2, the drive electrodes V3 and V4, the drive electrodes V5 and V6, and the drive electrodes V7 and V8 form a transfer stage, respectively. , V4, V6, V8) so that the potential of the drive electrodes (V1, V3, V5, V7) downstream in the transfer direction of the first transfer unit 20 is higher than the potential of the two transfer stages. The same drive signal may be supplied to the electrodes.

  Further, in the above description, one transfer stage is configured by combining two drive electrodes as one set, but three or more drive electrodes may be included in one transfer stage. When the number is three or more, the potential of the drive electrode upstream in the transfer direction may be higher than the potential of the drive electrode adjacent to the downstream side of the drive electrode.

  In the above description, the potential of each of the two drive electrodes constituting one transfer stage is substantially constant, but one oblique electrode as disclosed in JP-A-11-317513 is used. The drive electrode may be configured such that the potential thereof is inclined downward from the upstream to the downstream in the transfer direction of the first transfer unit 20.

  FIG. 5 illustrates a case where the potential of each of the drive electrodes V <b> 1 to V <b> 8 illustrated in FIG. 2 is inclined low from the upstream to the downstream in the transfer direction of the first transfer unit 20 during the transfer operation of the first transfer unit 20. It is a figure which shows the potential flow of the n-type channel 20a. Here, it is assumed that the potential gradient is set so that the potentials of the two drive electrodes constituting one transfer stage are continuous at the boundary.

  As shown in FIG. 5, a potential slope inclined in the deep direction from upstream to downstream in the transfer direction is formed under the two electrodes constituting one transfer stage, and the drive signals φV1 to φV4 are sequentially switched. Charges are transferred in the transfer direction. Even if it is such a structure, the effect similar to the effect mentioned above can be acquired. When the oblique electrode is used, the potential of the n-type channel 20a becomes a slope shape instead of a step shape, so that the charge transfer efficiency can be further improved.

The top view which shows schematic structure of the solid-state image sensor for describing embodiment of this invention The elements on larger scale which show typically the schematic structure of the 1st transfer part shown in FIG. The figure which shows the potential flow of an n-type channel at the time of transfer operation | movement of the 1st transfer part of the solid-state image sensor of this embodiment. The top view which shows the other schematic structure of the solid-state image sensor for describing embodiment of this invention The figure which shows the potential flow of an n-type channel at the time of transfer operation | movement of the 1st transfer part of the solid-state image sensor of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photoelectric conversion element 20 1st transfer part 20a n-type channel 40 2nd transfer part 50 Output part 60 Charge read-out area | region 100 Silicon substrate 200 Solid-state image sensor V1-V8 Drive electrode

Claims (2)

A number of photoelectric conversion elements arranged in a row direction and a column direction orthogonal thereto, a first transfer unit that transfers charges read from the plurality of photoelectric conversion elements in the column direction, and the first transfer unit A solid-state imaging device having a second transfer unit that transfers the charge transferred from the second transfer unit in the row direction and an output unit that outputs a signal according to the charge transferred from the second transfer unit,
The first transfer unit composed of a plurality of transfer stages is driven in four phases by drive signals φV1, φV2, φV3 and φV4,
Each of the transfer stages is composed of two drive electrodes arranged adjacent to each other in the charge transfer direction and supplied with one of the drive signals, and a channel region formed below the two drive electrodes .
The channel region has a constant impurity concentration throughout the first transfer part,
The two drive electrodes are set such that the potential of the drive electrode located upstream in the charge transfer direction is higher than the potential of the drive electrode located downstream.
Two of the transfer stages are connected to one of the photoelectric conversion elements,
Each of the drive signals φV1, φV2, φV3, and φV4 is supplied to the drive electrodes of a total of four transfer stages connected to the two photoelectric conversion elements arranged adjacent to each other in the column direction, and the first transfer unit The solid-state imaging device in which the potential of the channel regions of the four transfer stages becomes deeper from the upstream to the downstream in the transfer direction when transferring charges . The solid-state imaging device according to claim 1,
A solid-state imaging device that is inclined so that the potential of the drive electrode decreases from upstream to downstream in the transfer direction .

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