1. Field of the Invention
This invention relates to a multilayer deposition multipixel image pickup device used with digital camera, television camera image pickup, etc., and in particular to a highly sensitive multilayer deposition multipixel image pickup device with a large number of pixels.
2. Description of the Related Art
The competition in developing image pickup devices for still images by the manufacturers proceeds after advance notice of market introduction of electronic still cameras in 1982, especially after the advent of digital cameras in 1995. The theme of the development is to provide the device with a large number of pixels by making pixels finer, and when the 21st century is entered, an image pickup device with a pixel size of 3μ has also been realized (refer to CCD/CMOS image sensor nokisotoouyou, written by YONEMOTO Kazuya, published by CQ Shuppansha, page 16).
A conceptual drawing of a color image pickup device in a relate art is provided in FIG. 21 of U.S. 2003/0209651A1. In a single plate system shown in the drawing, a part of light is absorbed in a color filter and the sensitivity is degraded. For example, light passes through a red filter, whereby blue and green are lost in color filter, and only one third of light at the maximum is used. Making finer pixels is equivalent to lessening the area of a color filter 701 in the drawing and thus there is a tradeoff between making finer pixels and the sensitivity. Thus, in the single plate system, it is difficult to provide compatibility between making finer pixels and ensuring the necessary sensitivity in theory.
The technical conception of the multilayer deposition multipixel image pickup device was proposed from long ago as disclosed in JP-A-58-103165. The deposition type would eliminate the need for a color filter accompanied by a loss of light and the need for a complicated step of a microlens, etc., and would be able to also enhance the light use area percentage of each color and therefore the merit of becoming means for breaking through the tradeoff between making finer pixels and the sensitivity was recognized sufficiently, but it was not followed by development of an art for embodying it.
Then, the concept of the multilayer deposition type was embodied by a method commonly called Foveon system for separating color in the depth direction by a deposition light reception section using wavelength dependency of the absorption coefficient of Si as disclosed in U.S. Pat. No. 5,965,875. However, in the invention disclosed in U.S. Pat. No. 5,965,875, there is a tradeoff between the sensitivity and color separation property and either becomes unsatisfactory.
As a mode of the system improving the color separation property, U.S. 2003/0209651A1 discloses a system using a light reception section of an organic semiconductor and an inorganic semiconductor photosensitive layer on a Si substrate in combination. That is, FIG. 1 of the specification of U.S. 2003/0209651A1 discloses an image pickup device having a configuration wherein green color is received in a first light reception section, blue color is received in a second light reception section after passing through the first light reception section, and red color is received in a third light reception section after passing through the first and second light reception sections.
Further, Japanese Patent No. 3315213 also discloses a multilayer deposition multipixel image pickup device having multilayer organic monolayer (molecular film) light reception elements for absorbing light of different colors deposited on an Si substrate.
However, the deposition multipixel image pickup device having an array of pixels on the substrate, the pixels provided by depositing light reception elements each made up of an electromagnetic absorption and photoelectric conversion part, a charge transfer and read part, and a plurality of contact parts for coupling both the parts is more excellent in sensitivity than the single plate system having an array of undeposited pixels, but higher sensitivity is still required. The deposition multipixel image pickup device is inferior in color separation to the single plate system for separating color light through an optical filter, and the resolution tends to become unsatisfactory as compared with the single plate system. Because of the deposition structure, shading also easily occurs.
The pixel size becomes smaller and the sensitivity becomes lower with the progress of a higher number of pixels to provide a fine image. Thus, still higher sensitivity and improvement in degradation of the image quality accompanying deposition are also required for the deposition multipixel image pickup device advantageous for higher sensitivity.
The above-described related arts and knowledge relevant to the invention are described in the following documents: