JP2005243946A - Solid-state imaging device and driving method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reading out signal charges from a pixel in a certain direction, such as a CCD image pickup device having a V double density structure, in which the number of pixels in a certain direction is multiplied by a predetermined number of effective resolutions. In a solid-state imaging device having a first electrode between them and a second electrode corresponding to each pixel, the signal charge readout characteristic is improved without increasing the readout voltage.
In a solid-state imaging device in which a plurality of pixels 2 are arranged, the number of pixels in a certain direction is set to a predetermined number times the effective resolution, and the pixels are arranged between a predetermined number of adjacent pixels 2. A region 23 is provided that allows the signal charge to move at the same time. When reading out signal charges from the pixels 2, a read voltage is applied to the second electrodes 12 corresponding to each pixel 2 and the first electrodes 11 existing between the predetermined number of pixels 2.
[Selection] Figure 5

Description

  The present invention relates to a solid-state imaging device and a driving method thereof, and more particularly, to an improvement in readout characteristics of a solid-state imaging device having a V double density structure.

  Conventionally, in a CCD imaging device, field readout is most commonly performed using a vertical transfer register having two transfer electrodes in the first layer and the second layer for one pixel. .

  On the other hand, in recent years, a CCD image pickup device in which transfer electrodes of a vertical transfer register per pixel are formed in three layers or four layers has appeared in order to enable all pixel readout. However, such a CCD imaging device has a drawback that the structure of the vertical transfer register is complicated.

  Therefore, a CCD image pickup device having a V (Vertical) double-density structure has been proposed as a CCD image pickup device that realizes all-pixel readout with two layers of transfer electrodes of a vertical transfer register per pixel. This is because the number of pixels in the vertical direction is double the effective vertical resolution, and the signal charges read from two adjacent pixels in the vertical direction are added (mixed) and transferred vertically to read out all pixels. (For example, refer to Patent Document 1).

  FIG. 7 is a plan view showing a detailed structure of an imaging region of a conventional CCD image pickup device having a V double density structure, in which the direction of arrow V is the transfer direction of the vertical transfer register and the direction of arrow H is the transfer direction of the horizontal transfer register. It is. For example, a plurality of light receiving portions (pixels) 51 made of photodiodes are arranged in a matrix. Each light-receiving unit 51 has a vertical size that is ½ of the original size by doubling the number in the vertical direction to the effective vertical resolution.

  A first transfer electrode 52 and a second transfer electrode 53 of the vertical transfer register are formed on the left side (or the right side) in the horizontal direction with respect to each light receiving unit 51. Yes. The signal charge accumulated in the light receiving unit 51 is read out to the vertical transfer register through a reading area (not shown). The region other than the light receiving portion 51 is covered with a light shielding film 54 for shielding the vertical transfer register (the light shielding film 54 is drawn only for the peripheral portion of the light receiving portion 51 in the figure).

  FIG. 8 is a cross-sectional view (AA ′ cross-sectional view in FIG. 7) showing the detailed structure of the image pickup region of the CCD image pickup device having the V double-density structure. Yes. A P-type well region 62 is formed on the N-type semiconductor substrate 61, and an N-type region 63 and a P-type surface region 64 constituting the light receiving unit 51 (FIG. 7) are formed on the P-type well region 62. . An element isolation region 65 is formed between the light receiving portions 51 to prevent mixing of signal charges between the light receiving portions 51.

  On the semiconductor substrate 61, transfer electrodes 52 and 53 (FIG. 7) for the respective light receiving portions 51 are formed with an insulating film 66 therebetween. The area other than the light receiving portion 51 is covered with a light shielding film 54 (FIG. 7). When light enters the light receiving portion 51, incident light is photoelectrically converted in the N-type region 63 to generate signal charges, and the signal charges are accumulated in the P-type surface region 64.

All pixel readout by this CCD image pickup device is performed by adding signal charges read out from two adjacent pixels in the vertical direction like the two light receiving portions 51 depicted in the center in FIGS. Done by transferring.
JP 2000-184286 A (paragraph numbers 0004 to 0005, FIG. 3)

  By the way, in a CCD image pickup device having a V double density structure, the width of the signal charge read-out portion is halved when the pixel size in the vertical direction becomes ½ of the original size. There arises a problem that the readout characteristic of the signal charge is deteriorated.

  9 and 10, in order to explain this problem, among the transfer electrodes 52 and 53 shown in FIGS. 7 and 8, a read voltage is applied to read the signal charge from each light receiving portion 51. It is the figure which attached the oblique line to each transfer electrode. By applying a read voltage to the transfer electrode 53 in the second layer located below each light receiving portion 51 in the vertical direction, signal charges are read from the light receiving portions 51. A read voltage is not applied to the transfer electrode 52 of the first layer existing between the light receiving portions 51 in order to avoid leakage of signal charges beyond the element isolation region 65.

  Since each light receiving portion 51 has a vertical size that is ½ of the original size, the width of the transfer electrode 53 is also halved correspondingly, and as a result, the width of the signal charge reading portion is reduced. Since it is halved, the read characteristics are deteriorated.

  In order to prevent such deterioration of the read characteristics, it is conceivable to increase the read voltage applied to the transfer electrode 53. However, when this readout voltage is increased, another problem arises in that the reliability of the insulating film 66 shown in FIG. 8 is lowered, or readout noise peculiar to the CCD image sensor is deteriorated.

  In view of the above-mentioned points, the present invention is a means capable of reading the signal charge from these pixels while the number of pixels in a certain direction is made a predetermined number times the effective resolution, such as a CCD image pickup device having a V double density structure. As shown in FIG. 7, the first electrode (corresponding to the first-layer transfer electrode 52 in FIGS. 7 and 8) existing between adjacent pixels and the second electrode corresponding to each pixel (FIGS. 7 and 8). In the solid-state imaging device having the second-layer transfer electrode 53), it is an object to improve the signal charge readout characteristics without increasing the readout voltage.

  In order to solve this problem, a solid-state imaging device according to the present invention is a solid-state imaging device in which a plurality of pixels are arranged. The number of pixels in a certain direction is a predetermined number of times the effective resolution, and a predetermined number of adjacent pixels. Each pixel is provided with a region that allows signal charges to move between the pixels.

  In this solid-state imaging device, the number of pixels in a certain direction is a predetermined number of times the effective resolution, and there is an area between the predetermined number of adjacent pixels that allows signal charges to move between the pixels. Provided.

  Accordingly, the number of pixels in a certain direction is made a predetermined number times the effective resolution, such as a CCD image pickup device having a V double density structure, and a signal charge can be read from these pixels. If the present invention is applied to a solid-state imaging device having a first electrode present in the pixel and a second electrode corresponding to each pixel, not only the second electrode but also the predetermined electrode is read out when reading signal charges from the pixel. By applying a read voltage to the first electrode existing between several pixels, the signal charges of these pixels can be read out through the region between the pixels (for example, an N-type region).

  At this time, the signal charges of the predetermined number of pixels are mixed through the region between the pixels before reading. However, since all signal readout is based on the premise that signal charges read from these pixels are added (mixed), there is no problem in mixing the signal charges of those pixels before readout.

  As described above, by performing readout using three electrodes (a second electrode corresponding to each pixel and a first electrode existing between the pixels) per two adjacent pixels, the signal charge is reduced. Since the width of the readout portion is increased, the signal charge readout characteristics can be improved without increasing the readout voltage.

  Here, as an example, it is preferable to integrally form regions constituting a predetermined number of adjacent pixels. Thereby, when a read voltage is applied to the first electrode existing between the pixels, the signal charge is smoothly moved between the pixels, so that the read characteristics are further improved.

  The solid-state image sensor according to the present invention can also be applied to an XY address type solid-state image sensor such as a CMOS sensor. Even in such a case, the signal charges of a predetermined number of adjacent pixels can be mixed and read out.

  Next, in the solid-state imaging device driving method according to the present invention, a plurality of pixels are arranged, the number of pixels in a certain direction is a predetermined number of times the effective resolution, and between a predetermined number of adjacent pixels, A region that enables movement of signal charges between these pixels is provided, and as a means for reading signal charges from these pixels, a first electrode that exists between adjacent pixels, In a method for driving a solid-state imaging device having a second electrode corresponding to a pixel, when reading out signal charges from these pixels, the second electrode corresponding to each pixel and the predetermined number of pixels A read voltage is applied to the first electrode existing in the substrate.

  In this driving method, the solid-state image pickup device according to the present invention described above is configured such that the number of pixels in a certain direction is a predetermined number times the effective resolution, such as a CCD image pickup device having a V double density structure. When applied to a solid-state imaging device having a first electrode existing between adjacent pixels and a second electrode corresponding to each pixel as a means capable of reading out charges, signal charges from the pixels At the time of reading, a reading voltage is applied to the second electrode corresponding to each pixel and the first electrode existing between a predetermined number of pixels.

  At this time, reading is performed by using three electrodes (a second electrode corresponding to each pixel and a first electrode existing between the pixels) per two adjacent pixels, and the signal charge Since the width of the readout portion is increased, it is possible to improve the signal charge readout characteristics without increasing the readout voltage during readout of all pixels.

  According to the present invention, the number of pixels in a certain direction is set to a predetermined number times the effective resolution as in a CCD image pickup device having a V double density structure, and the signal charges can be read out from these pixels adjacent to each other. In the solid-state imaging device having the first electrode existing between the pixels and the second electrode corresponding to each pixel, reading is performed using three electrodes per two adjacent pixels, so that the signal charge Since the width of the read-out portion becomes large, it is possible to improve the signal charge read-out characteristics without increasing the read-out voltage when reading out all pixels.

  Further, even in an XY address type solid-state imaging device such as a CMOS sensor, for example, an effect is obtained that signal charges of a predetermined number of adjacent pixels can be mixed and read.

  Hereinafter, an example in which the present invention is applied to a CCD image pickup device having a V double density structure will be specifically described with reference to the drawings. FIG. 1 is a plan view showing the overall configuration of a CCD image sensor to which the present invention is applied. In the CCD imaging device 1, a plurality of light receiving portions (pixels) 2 made of, for example, photodiodes are arranged in a matrix. Each light receiving unit 2 has a vertical size that is ½ the original size by doubling the number in the vertical direction (the direction of arrow V in the figure) to the effective vertical resolution.

  The signal charges read from the light receiving units 2 in each vertical column are transferred in the vertical direction by the vertical transfer registers 3 corresponding to the vertical columns. The signal charges transferred by each vertical transfer register 3 are transferred in the horizontal direction (in the direction of arrow H in the figure) by the horizontal transfer register 4, converted into a voltage signal by the output amplifier 5, and output from the output terminal 6. Is done.

  FIG. 2 is a plan view showing the detailed structure of the image pickup region of the CCD image pickup device. The same parts as those in FIG. 1 are denoted by the same reference numerals (the directions of arrows V and H are the same as those in FIG. 1, respectively. , Horizontal).

  The first transfer electrode 11 and the second transfer electrode 12 of the vertical transfer register 3 (FIG. 1) are on the left side (or may be the right side) in the horizontal direction with respect to each light receiving unit 2. And are formed. The signal charge accumulated in the light receiving unit 2 is read out to the vertical transfer register 3 through a reading area (not shown). The region other than the light receiving unit 2 is covered with a light shielding film 13 for shielding the vertical transfer register 3 (the light shielding film 13 is drawn only for the peripheral portion of the light receiving unit 2 in the figure).

  FIG. 3 is a cross-sectional view (cross-sectional view taken along the line A-A ′ in FIG. 2) showing the detailed structure of the image pickup region of the CCD image pickup device, and the same parts as those in FIG. A P-type well region 22 is formed on an N-type semiconductor substrate 21, and an N-type region 23 and a P-type surface region 24 constituting the light receiving unit 2 (FIGS. 1 and 2) are formed on the P-type well region 22. Has been.

  Here, each light receiving unit 2 includes two light receiving units 2 adjacent in the vertical direction (lateral direction in the drawing) as one set, and each group of N-type regions 23 is integrally formed. An element isolation region 25 for preventing mixing of signal charges between the light receiving portions 2 is formed between different sets of light receiving portions 2.

  On the semiconductor substrate 21, transfer electrodes 11 and 12 (FIG. 2) for the respective light receiving portions 2 are formed with an insulating film 26 therebetween. A region other than the light receiving unit 2 is covered with a light shielding film 13 (FIG. 2). When light enters the light receiving unit 2, the incident light is photoelectrically converted in the N-type region 23 to generate a signal charge, and the signal charge is accumulated in the P-type surface region 24.

  In this CCD image pickup device, since the N-type region 23 of the light receiving unit 2 exists over the lower side of the transfer electrodes 11 and 12, the N-type region is formed before the transfer electrodes 11 and 12 are formed at the time of manufacture. It is assumed that the region 23 is formed. However, after the N-type region 23 is formed and then the transfer electrodes 11 and 12 are formed, an N-type impurity may be introduced into the N-type region 23 in order to adjust the potential of the two light receiving portions 2 in the same set. . The P-type surface region 24 may be formed before the transfer electrodes 11 and 12 are formed, or may be formed after the transfer electrodes 11 and 12 are formed.

  4 and 5 are diagrams in which, among the transfer electrodes 11 and 12 shown in FIGS. 2 and 3, transfer electrodes to which a read voltage is applied when all pixels are read by the CCD image pickup device are hatched. is there. A read voltage is applied to the second-layer transfer electrode 12 positioned below each light-receiving unit 2 in the vertical direction, and the read-out voltage is read to the first-layer transfer electrode 11 existing between the same pair of light-receiving units 2. By applying a voltage, signal charges are read from each light receiving unit 2.

  At this time, the signal charges of the two light receiving portions 2 adjacent in the vertical direction are mixed through the common N-type region 23 before reading. However, since it is assumed that signal charges read from the light receiving units 2 are added (mixed) in all pixel reading, it is quite a problem that the signal charges of the light receiving units 2 are mixed before reading. There is no.

  In this way, three transfer electrodes (the second-layer transfer electrode 12 corresponding to each light-receiving unit 2 and the first-layer transfer electrode 11 existing between the light-receiving units 2) per two light-receiving units 2 are provided. When reading is performed using this, the width of the signal charge reading portion is increased, as is apparent from comparison with FIGS. 9 and 10 described above. Thereby, the read characteristic of the signal charge from the light receiving unit 2 is improved without increasing the read voltage.

  Since the N-type regions 23 of the light receiving portions 2 are integrally formed, when a read voltage is applied to the transfer electrode 11 of the first layer existing between the light receiving portions 2, the light reception is performed. Since the signal charges are smoothly moved between the portions 2, read characteristics are further improved.

  In the above example, the N-type regions 23 of the light receiving portions 2 of the same group (two adjacent in the vertical direction) are integrally formed. However, as another example, an element isolation region may not be provided between the light receiving portions 2 as shown in FIG. Also in this case, by applying a read voltage to the transfer electrode 11 of the first layer existing between the light receiving portions 2, the width of the signal charge read portion is also increased (via the P-type well region 22). As a result, the signal charge moves between the light receiving portions 2), so that the read characteristics are improved.

  Moreover, in the above example, the example which applied this invention to the CCD image pick-up element of V double dense structure was shown. However, the present invention is not limited to this, and the number of pixels in a certain direction is set to a predetermined number times the effective resolution, and the first electrode existing between adjacent pixels as a means for reading signal charges from these pixels. (Corresponding to the first-layer transfer electrode 11 in FIGS. 2 and 3) and a second electrode corresponding to each pixel (corresponding to the second-layer transfer electrode 12 in FIGS. 2 and 3). The present invention may be applied to any solid-state imaging device.

  In the above example, the example in which the present invention is applied to the CCD image pickup device in which the light receiving portions are arranged in a matrix and the interline transfer method is adopted as the transfer method has been shown. However, since the present invention is characterized by a structure and a method related to reading out signal charges from pixels, a CCD image sensor employing a frame transfer method or a CCD image sensor (line sensor) in which a light receiving portion is arranged one-dimensionally. ).

  The solid-state image sensor according to the present invention may also be applied to an XY address type solid-state image sensor such as a CMOS sensor. Even in such a case, signal charges of a predetermined number of adjacent pixels can be mixed and read out.

It is a figure which shows the whole structure of the CCD image pick-up element of the V double dense structure to which this invention is applied. It is a top view which shows the detailed structure of the imaging region of the CCD image pick-up element of FIG. FIG. 4 is a cross-sectional view taken along the line A-A ′ of FIG. 3. It is a figure which shows the transfer electrode which applies a read-out voltage by this invention. It is a figure which shows the transfer electrode which applies a read-out voltage by this invention. It is a figure which shows the modification of a structure of the CCD image pick-up element of the V double dense structure to which this invention is applied. It is a top view which shows the detailed structure of the imaging region of the CCD image pick-up element of the conventional V double dense structure. It is A-A 'sectional drawing of FIG. It is a figure which shows the transfer electrode which applies a read-out voltage with the CCD image pick-up element of the conventional V double dense structure. It is a figure which shows the transfer electrode which applies a read-out voltage with the CCD image pick-up element of the conventional V double dense structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 CCD image pick-up element 2 Light-receiving part 3 Vertical transfer register 4 Horizontal transfer register 5 Output amplifier 6 Output terminal 11 The 1st layer transfer electrode 12 of a vertical transfer register The 2nd layer transfer electrode 13 of a vertical transfer register Light shielding film 21 N Type semiconductor substrate 22 P-type well region 23 N-type region 24 of light-receiving part P-type surface region 25 of light-receiving part Element isolation region 26 Insulating film

Claims (5)

In a solid-state imaging device in which a plurality of pixels are arranged,
The number of pixels in a certain direction is a predetermined number of times the effective resolution,
A solid-state imaging device, characterized in that a predetermined number of adjacent pixels are provided with a region that allows signal charges to move between the pixels. The solid-state imaging device according to claim 1,
The solid-state image pickup device, wherein the region that enables the signal charge to move is an N-type region. The solid-state imaging device according to claim 1,
A solid-state imaging device comprising: the first electrode existing between adjacent pixels; and a second electrode corresponding to each of the pixels as means for reading signal charges from the pixels. element. The solid-state imaging device according to claim 1,
A solid-state image pickup device, wherein the regions constituting the predetermined number of the pixels are integrally formed. A plurality of pixels are arranged, the number of pixels in a certain direction is a predetermined number of times the effective resolution, and signal charges can be transferred between the adjacent pixels in a predetermined number of pixels. There is an area to
In a driving method of a solid-state imaging device having a first electrode existing between adjacent pixels and a second electrode corresponding to each of the pixels as means for reading signal charges from the pixels,
When reading signal charges from the pixels, a read voltage is applied to the second electrodes corresponding to the pixels and the first electrodes existing between the predetermined number of pixels. A method for driving a solid-state imaging device.

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