1. Field of the Invention
The present invention relates to a solid-state imaging device, which is an example of a semiconductor device for detection of physical amount distribution, and an imaging apparatus. Specifically, the present invention relates to a signal acquisition technique suitable for application to a solid-state imaging device or the like using a semiconductor device for detection of physical amount distribution in which a plurality of unit constituent elements with sensitivity to electromagnetic waves, such as light or radiant rays, input from the outside are arranged and which can read physical amount distribution, which is converted into electrical signals by the unit constituent elements, as electrical signals. In particular, the present invention relates to a structure of using a high-sensitivity pixel.
2. Description of the Related Art
A physical amount distribution detection semiconductor device in which a plurality of unit constituent elements (for example, elements) with sensitivity to electromagnetic waves, such as light or radiant rays, input from the outside are arranged in a line shape or in a matrix is used in various fields.
For example, in a field of visual equipment, a CCD (charge coupled device) type or MOS (metal oxide semiconductor) type or CMOS (complementary metal oxide semiconductor) type solid-state imaging device that detects a change of light (an example of an electromagnetic wave), which is an example of physical amount, is used. These solid-state imaging devices read physical amount distribution, which is converted into electrical signals by unit constituent elements (pixels in the solid-state imaging device), as electrical signals.
For example, the solid-state imaging device generates and accumulates signal charges by detecting electromagnetic waves, such as light or radiant rays, input from the outside in a photodiode, which is a photoelectric conversion element (light receiving element; photosensor) provided in an imaging portion (pixel portion) of a device portion, and reads the accumulated signal charges (photoelectrons) as image information.
In the case of a configuration for acquiring a color image, it is a mainstream to use an image sensor in which a color filter, which allows only a component having a specific wavelength to be transmitted therethrough, is arranged in each pixel and a required color component is restored by using a set of plurality of pixels.
Specifically, colors are distinguished by a color arrangement in which color reduction filters corresponding to, for example, red (R), green (G), and blue (B) colors, which are three primary colors, are used as a set of color filters and three primary color light components transmitted through the filters are separately detected by providing a semiconductor layer that detects light below the color filters. In addition, it may also be considered to use an arrangement in which white (Y), red (R), green (G), and blue (B) for luminance signal acquisition are combined. All the arrangements described above are called Bayer arrangements.
In a solid-state imaging element based on a single plate color method, each pixel has only information on a single color component as described above. Accordingly, for example, demosaic processing for restoring a required color component in each pixel by performing interpolation processing using color information on surrounding pixels is performed (for example, refer to JP-A-04-088784).
On the other hand, in a digital still camera or a movie camera, an improvement in quality of an image photographed under low illuminance has been an important issue in recent years. In the case of photographing an image under low illuminance, it is common to lower a shutter speed, to use a lens having a bright aperture value, or to use an external light source for visible light, such as a flash.
In this case, lowering the shutter speed causes hand trembling or blurring of a photographic subject. Moreover, in general, there is also a limitation in an aperture value of a lens. For this reason, it is difficult to realize the brightness more than a certain extent. In addition, in the case when the external light source for visible light is used, there is a problem that an atmosphere based on illumination in the place may be spoiled.
Since a color temperature is low under a low illuminance condition, a light source that emits a large amount of infrared light is used in many cases. In addition, if invisible light, such as infrared light, is used as auxiliary light, the atmosphere is hardly spoiled. Therefore, a technique of increasing effective photographing sensitivity under a light source including a large amount of invisible light, such as infrared light, has been demanded.
As an example of measures against the problems described above, it is considered to add white (Y) for high-sensitivity luminance signals in a known color coding arrangement which is basically used. For example, JP-A-04-088784 discloses signal processing for obtaining a high-sensitivity image using an imaging element to which a YRGB arrangement, in which white (Y) for luminance signals is added in the Bayer arrangement where red (R), green (G), and blue (B) are arranged in a square matrix, is applied. In this structure, signal processing for obtaining high resolution and high sensitivity is explained by using a white pixel of pixels arranged in a checker pattern assuming that a color filter array, in which white pixels are arranged in the checker pattern, is applied and none of the pixels sense components (for example, infrared light) other than visible light components.
That is, in the arrangement proposed in JP-A-04-088784, a Y pixel in the checker arrangement has sensitivity to almost the entire visible light. Accordingly, a signal larger than that in a case of a configuration where green (G) pixels are arranged in a checker pattern is obtained. For this reason, it is possible to obtain a satisfactory S/N ratio of signals in the checker arrangement, which influences resolution or luminance information, compared with a case of a checker arrangement of green pixels.