JPH0691659B2 - Image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an image sensor of a birch pieze CCD (VPCCD) type, and more specifically, an electronic still camera capable of improving photosensitivity to short wavelength light. The present invention relates to a dedicated image sensor.

(Prior Art) Conventionally, it has been an important theme to increase the photosensitivity in the characteristics of an image sensor. This point, frame transfer
The CCD (FTCCD) has a dedicated image pickup unit for photoelectric conversion, and since it can receive light over the entire area, it has essentially higher light utilization efficiency than other types of image pickup devices. But,
In the conventional FTCCD, the imaging part is covered with a gate electrode,
Since the photosensitivity to short-wavelength light is controlled by the absorption and reflection of light by this electrode, this maximum feature has not been fully utilized.

In order to solve this problem, it is considered to form an opening window in which the electrodes are not covered in the image pickup section, and one of them, a so-called birch fraise aids CCD, has been developed.

As shown in FIG. 3, one of the electrodes in the conventional two-phase transfer is replaced by the diffusion layer 1 in the channel (this is called a virtual gate), and this portion is used as an opening window. , The electric potential in the channel is controlled by the injection of impurities to enable the charge transfer.

(Problems to be solved by the invention) However, when a color filter is arranged in this VPCCD, the actual spectrum is still high on the long wavelength light side,
The short wavelength light side, that is, the blue sensitivity was insufficient. This is because the photosensitive region is composed of a portion without polysilicon (gate electrode) and a portion with polysilicon, and therefore light absorption and the like still occur in the portion with polysilicon.

An object of the present invention is to provide an image sensor dedicated to a still camera, which has improved sensitivity on the short wavelength light side and improved overall sensitivity.

(Means for Solving Problems) In order to achieve the above object, the image sensor according to the present invention is configured as follows. That is, in an image sensor in which signal charges of photoelectric conversion elements arranged in a matrix are transferred by a transfer electrode having a vertical phase CCD structure, a color filter having a stripe arrangement in which the same color is arranged in the vertical direction is arranged on a pixel. The pixel surface corresponding to at least short wavelength light has a complete aperture window with the polysilicon transfer electrode removed, and between the short wavelength light pixel and the medium wavelength light or long wavelength light pixel. A transfer gate is provided, and after the signal charge of the pixel of the medium wavelength light or the long wavelength light provided with the transfer gate is read out, the signal charge of the pixel of the short wavelength light is read through the transfer gate. This is achieved by an image sensor which is read out after being field-shifted to a line of pixels of the medium wavelength light or the long wavelength light.

(Operation) In the image sensor according to the present invention, at least for short wavelength light, the surface of the corresponding photoelectric conversion element is completely opened and the polysilicon transfer electrode is removed. Therefore, the image sensor operates by the interline transfer (IT) method. On the other hand, for long-wavelength light or medium-wavelength light, the image pickup unit is composed of a birch fraise aids CCD. So, for example, R,
By using the G and B stripe filters, the charge transfer process is first performed with the color R that is long-wavelength light or medium-wavelength light.
Alternatively, the signal charges formed in the G photoelectric conversion element are single-phase driven by the vertical phase electrodes and transferred to the signal storage unit during the signal transfer cycle. During this period, the signal charge of the color B, which is short-wavelength light, remains in the photoelectric conversion element. All the signal charges of color R or G are transferred to the signal storage unit,
When further read out from the horizontal CCD, the color B signal charge is then field-shifted to the color R or G photoelectric conversion element. That is, at this time, the photoelectric conversion element of the color R or G operates as a vertical transfer line of the color B, and transfers the signal charge of the color B to the signal storage unit similarly to the color R or G. Thereafter, the charge of color B is read out via the horizontal CCD.

It is needless to say that during the vertical transfer of the color B, the light incident on the image pickup section must be blocked by some kind of light blocking means, for example, a mechanical shutter.

As described above, in the image sensor according to the present invention, at least the color of the short wavelength light has a window in which the polysilicon transfer electrode is completely opened, and for the long wavelength light or the medium wavelength light, the birefringence aids. The electrode has a partial opening window to improve the overall sensitivity and further improve the sensitivity of short wavelength light.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

1 is a block diagram showing an image pickup section of an image sensor according to the present invention. The image pickup unit 10 has photoelectric conversion elements arranged in a matrix, and a micro color filter is arranged on the image pickup unit. The micro color filter has three colors R, G, B corresponding to each photoelectric conversion element. The micro color filter having the structure according to the present invention comprises a stripe array in which the same color is arranged in the vertical direction. This sequence is schematically indicated by the symbols R, G, B in the figure. The photoelectric conversion elements arranged under the colors R and G also have a role of a charge transfer element, and the transfer thereof is single-phase driven by a birch phase CCD. That is, in this Birch phase CCD structure, as shown in FIG. 3 for explaining the conventional device, one of the two electrodes in the two-phase driving is substituted by the diffusion layer in the channel (virtual electrode). The portion is the opening window 2. Furthermore, since the virtual electrode alone does not have a sufficient transfer function, the substrate concentration is changed by ion implantation to facilitate the movement of the signal charge to the lower side of the virtual electrode and further to the next electrode. On the other hand, the photoelectric conversion element of the pixel corresponding to the color B does not have the charge transfer function itself. Therefore, the element surface is provided with a complete opening window 4 from which the polysilicon transfer electrode 3 is removed. The signal charge generated based on the color B is vertically transferred by using the transfer line of the adjacent color R. Therefore, the transfer gate 5 is provided between the color B photoelectric conversion element and the color R photoelectric conversion element to control the field shift of the color B signal charge. As is clear from the above description, in this embodiment, the photoelectric conversion element for the color R is the color R
It performs the three functions of photoelectric conversion and charge transfer of B, and charge transfer of color B.

In the figure, the hatched portion is a channel stopper formed on a silicon substrate, and the portion surrounded by the channel stopper is a photoelectric conversion element and a charge transfer element, that is, a self-scanning CCD having a birch flueze electrode structure. A shift register is formed.

The signal charges generated by the photoelectric conversion elements of colors R and G are
The signals are sequentially sent to the accumulating section (shown by arrows in the figure) from output ends near the signal accumulating section (not shown) via the photoelectric conversion elements themselves. When the transfer of all the charges of the colors R and G is completed, these signal charges are then sequentially read from a horizontal CCD (not shown). This series of colors for R and G
When the transfer / read process for
The signal charge generated in the photoelectric conversion element for color B is field-shifted to the photoelectric conversion element for color R in the empty state by opening the transfer gate 5 (indicated by an arrow in the figure). The field charge of the color B, which has been field-shifted to the photoelectric conversion element for the color R, is vertically transferred in the same manner as the charge of the color R or the color G described above (indicated by an arrow in the figure), and is further transferred to the horizontal CCD. Read through.

In the above embodiment, the charge storage unit is provided for charge transfer, but the present invention omits the storage unit and operates only in the so-called full frame mode in which the image pickup unit and the horizontal CCD are used. It may have a structure.

FIG. 2 illustrates another embodiment of the present invention. In this embodiment, the photoelectric conversion element of the color G of the embodiment shown in FIG. 1 has the completely open window 7 by removing the polysilicon transfer electrode 6 like the color B. Therefore, the charge transfer is performed using the transfer line of the color R. Therefore, like the transfer of the color B, the transfer gate 8 is provided between the photoelectric conversion element for the color G and the photoelectric conversion element for the color R. Then, the signal transfer is performed for the color R and then sequentially for the color B or G. Therefore, at this time, since it is difficult for the transfer gate 9 between the color B and the color R and the transfer gate 8 between the color G and the color R to operate at the same time, the respective threshold voltages are different.

(Effects of the Invention) As described above, according to the image sensor of the present invention, by forming the image pickup unit with the VPCCD structure, it is possible to improve the sensitivity on the long wavelength light side by having a partial opening on the virtual electrode. Particularly, on the short wavelength light side, by forming a complete opening in which the transfer electrode is excluded, a device having a higher sensitivity than a device having a VPCCD structure can be obtained. Further, since the VPCCD substantially has only one transfer electrode, the structure can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining one embodiment of the present invention, FIG. 2 is a block diagram for explaining another embodiment of the present invention, and FIG. 3 is a diagram for explaining a conventional birch fraise aids CCD. Is. 2 …… Opening window, 3,6 …… Polysilicon transfer electrode, 4,7 ……
Fully open window, 5,8,9 …… Transfer gate

Claims (1)

[Claims] 1. In an image sensor in which signal charges of photoelectric conversion elements arranged in a matrix are transferred by a transfer electrode having a virtual phase CCD structure, a color filter having a stripe arrangement in which the same color is vertically arranged is arranged on a pixel. The pixel surface corresponding to at least the short-wavelength light has a complete opening window with the polysilicon transfer electrode removed, and the short-wavelength light pixel and the medium-wavelength light or long-wavelength light pixel are arranged. A transfer gate is provided between the transfer gate and the signal charge of the pixel of the medium wavelength light or the long wavelength light in which the transfer gate is provided, and then the signal charge of the pixel of the short wavelength light passes through the transfer gate. An image sensor which is read out after being field-shifted to a line of pixels of the medium wavelength light or the long wavelength light.