Patent Publication Number: US-2005133879-A1

Title: Solid-state imaging device, signal processing device, camera, and spectral device

Description:
BACKGROUND OF THE INVENTION  
      (1) Field of the Invention  
      The present invention relates to solid-state imaging devices used in digital cameras and the like, and in particular to a technique for filters that cut light of unnecessary wavelength in a wavelength range to which photodiodes in a solid-state imaging device are sensitive, and for generating color signals from electric signals generated via the filters.  
      (2) Description of the Related Art  
      Conventional solid-state imaging devices perform color separation according to a color imaging method with either a single sensor device or with multi sensor devices. In the color imaging method with multi sensor devices, color signals are obtained by separating colors of an image with a color separation prism, and converting the separated image into an electric signal with use of three or four solid-state imaging devices. In contrast, in the color imaging method with a single sensor device, color signals are obtained by separating images with use of three or four color on-chip color filters formed in the one solid-state imaging device that converts the color separated image into electrical signals. The color imaging with a single sensor method uses either a primary color filter or a complimentary color filter, depending on the colors into which images are to be separated. For example, in the case of a primary color filter, an image is separated into three colors: red (R), green (G) and blue (B), and in the case of a complimentary color filter, an image is separated into four colors: cyan (Cy), magenta (Mg), yellow (Ye) and green (G) (for example, refer to Document 1).  
      Regardless of whether the method used uses a single sensor or multi sensors, a common feature is that an image is divided into two-dimensionally arranged pixels, and converted into electric signals.  
      For this reason, the following describes only a solid-state imaging device that uses a single sensor, and omits a description of the color imaging method with multi sensor devices.  
      Furthermore, since the method used up to converting the image to an electric signal is common to both methods, and the only difference is the colors obtained by separation, the color imaging method with a single sensor device is described as using the primary color filter rather than the complimentary color filter.  
      Structure of a Conventional Solid-State Imaging Device  
       FIG. 15A  is an upper surface view of a photoelectric conversion unit in a conventional solid-state imaging device, and  FIG. 15B  shows a cross section J-J′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that the pixels in the photoelectric conversion unit  10  are grouped in clusters called pixel units, and for brevity, only one of the pixel units (two by two pixels) is shown here.  
      As can be seen from  FIGS. 15A and 15B , the photoelectric conversion unit  10  is composed of pixels arranged two-dimensionally. Each pixel unit corresponds to one pixel that is the smallest unit of an image.  
      The pixels  1  to  4  have a structure in which photodiodes  12  are formed in a semiconductor substrate  11 , an insulating film  13 , a light shield film  14 , an insulating film  16  for planarizing, and the color filters  17   r ,  17   b , and  17   g  (one per pixel) are formed in the stated order on the semiconductor substrate  11  in which the photodiodes  12  have been formed. The light shield film  14  is formed with apertures  15  therein. The photodiode  12 , insulating film  13 , and light shield film  14  are formed according to a wafer fabrication process, and the color filters  17   r ,  17   b , and  17   g  is formed on the surface of the insulating film  16  according to an on-chip color filter manufacturing process.  
      This on-chip color filter manufacturing process consists of coating the surface of the insulating film with a resin film, exposing and the resin film using a hot mask, and then developing the resin film, thereby forming a dye pattern. The color filter is then formed in the pattern with pigment, dye, or the like.  
      A color is assigned to each pixel according to the Bayer pattern, and a color filter of the assigned color is formed for each pixel. Here, each of three pixels making up one group has a different one of the colors. As one example, as shown in the drawings, pixels  1  and  4  each have a green color filter  17   g , pixel  2  has a blue color filter  17   b , and pixel  3  has a red color filter  17   r.    
      Furthermore, an infrared ray cut filter  18  is provided above the color filters  17   r ,  17   g  and  17   b  of the pixels  1  to  4 .  
      Light incident on the photoelectric conversion unit  10  passes through the infrared ray cut filter  18 , then the color filter  17   r ,  17   g , or  17   b , and passes through the aperture  15  to be photoelectric converted to electrons by the photodiode  12 .  
       FIG. 16  is a graph showing spectral sensitivity characteristics of a photodiode and sensitivity characteristics of the human eye.  
      In this drawing, a curve  51  shows spectral sensitivity of a photodiode that uses silicon PN junction, while a curve  52  shows sensitivity characteristics of the human eye.  
      As shown by the curve  51 , of wavelengths ranging from visible light through to infrared rays, a photodiode that uses silicon PN junction is particularly sensitive to light in a range 300 nm to 1100 nm, with sensitivity peaking at 600 nm to 750 nm.  
      Here, visible light is a type of electromagnetic wave in a range of 380 nm to 780 nm, and colors such as violet, blue, green, orange and red (in order of shortness of wavelength) are perceptible by the human eye. Infrared rays are a type of electromagnetic wave whose wavelength is longer than visible light, and are divided, in order of closeness to visible light, into near infrared light (0.78μ to 3μ), mid-infrared light (3μ to 30μ), and far infrared light (30μ to 1 mm).  
      As can be seen from the curve  52 , in contrast to the photodiode, visual sensitivity indicated by the sensitivity characteristics of the human eye peaks with light of a wavelength of 555 nm (green light), and decreases as the wavelength becomes both shorter (towards the blue side) and longer (towards the red side).  
      The curves  51  and  52  demonstrate that it is necessary to eliminate the effect of infrared rays beyond the visible range on the photodiodes  12  as much as possible in solid-state imaging devices for digital cameras. This is because it is important to be able to measure the amount of light in a range visible to humans.  
      The infrared filter  18  is provided in the photoelectric conversion unit  10  for this reason.  
      A certain level of performance in photoelectric conversion is achieved in the photoelectric conversion unit  10  by providing color filters  17   r ,  17   g  and  17   b  above the photodiodes  12  in order to obtain color signals, coupled with the infrared ray cut filter  18  further provided above the color filters  17   r ,  17   g  and  17   b.    
      However, in addition to the wafer fabrication process, an on-chip color filter manufacturing process is necessary for forming the color filters and the infrared ray cut filter when manufacturing the solid-state imaging device. In other words, the necessity of performing a plurality of manufacturing processes gives rise to a problem that solid-state imaging devices are time consuming and costly to manufacture.  
      In addition, it is necessary to manufacture color filters and infrared ray cut filters having precise spectral characteristics if a photoelectric conversion unit having performance above a certain level is to be manufactured. This also causes problems of reduced yield and high manufacturing costs.  
      Document 1: ANDO, Takao and KOMOBUCHI, Hiroyoshi,  Kotai Satuzo Soshi no Kiso, Denshi no Me no Shikumi  ( The Fundamentals of Solid - State Imaging Devices: The Structure of Electronic Eyes ), Nihon Riko Shuppankai, Dec. 5, 1999, pp. 183-188  
     SUMMARY OF THE INVENTION  
      In view of the described problems, the object of the present invention is to provide a solid-state imaging device, a signal processing device that generates color signals output by the solid-state imaging device, a camera in which the solid-state imaging device is used, and a spectral device, that enable reduced manufacturing time and cost, and improve yield, while also achieving high picture quality equivalent to or greater than a conventional solid-state imaging device.  
      In order to solve the state problem, the present invention is a solid-state imaging device, including: a plurality of photodiodes that each convert received light to an electric signal; and a light shield film having a plurality of apertures formed therein, and provided above and isolated from the photodiodes by an insulating film sandwiched between the light shield film and the photodiodes, wherein the apertures enable light of a wavelength below a predetermined wavelength to pass through.  
      According to the stated structure, in the solid-state imaging device of the present invention, the apertures provided in the light shield film function as high pass filters, and enable light of the predetermined wavelength or greater to be cut off. Specifically, an infrared ray cut filter and color cut filters can be omitted from the solid-state imaging device because the apertures in the light shield film cut off light having a wavelength longer than a certain wavelength. Furthermore, the precision with which the infrared ray cut filter blocks infrared light and the spectral characteristics of the color filters can be eased considerably.  
      For example, if the predetermined wavelength is a wavelength at the edge of visible light, and apertures that cut off a wavelength at the edge of visible light are provided in the light shield film, the precision with which the infrared filter cuts off infrared light can be eased considerably.  
      This is because even if infrared rays were to pass through the infrared ray cut filter, these infrared rays would be cut off by the apertures and therefore not reach the photodiodes.  
      Similarly, the precision of the spectral characteristics of the color filters in regard to wavelengths longer than visible light that is intended to pass through the color filters can be eased considerably.  
      In other words, the infrared filter can be omitted, or be provided but with considerably reduced precision in cutting off infrared light, and the color filters can be omitted, or be provided but with considerably reduced precision of the spectral characteristics in regard to wavelengths longer than visible light that is intended to pass through the color filters. As a result, the solid-state imaging device manufacturing process can be simplified, and yield of infrared ray cut filters and color filters can be improved considerably.  
      Consequently, the stated structure enables reduced solid-state imaging device manufacturing time, reduced cost, and improved yield.  
      Furthermore, material characteristics of the infrared filter and the color filters can be eased, and the materials used for the infrared filter and the color filters can be selected from an expanded range of materials.  
      Furthermore, the photodiodes may correspond respectively to pixels that are each a minimum unit of an image that is taken, and each of the photodiodes may have a different one of the apertures provided thereabove.  
      According to the stated structure, the frequency of light received can be limited for each pixel. Therefore, the color filter can be omitted from each pixel, or the spectral characteristic of the infrared filter and the color filters can be eased considerably.  
      Furthermore, a shape and a dimension of each aperture may be defined according to the predetermined wavelength.  
      According to the stated structure, the wavelength cut off by the apertures can be changed by changing the shape and dimensions of the apertures.  
      Furthermore, the apertures may be made up of N (N being a natural number) different types of the apertures, the predetermined wavelength may be different for each type of aperture, the photodiodes are N in number, and each of the N photodiodes may have an aperture of a different one of the N types provided thereabove.  
      According to the stated structure, electric charge that is generated according to differing wavelengths can be gathered in each photodiode. Therefore, an electric signal can be obtained that is equivalent to an electric signal of light of a frequency that passes through a color filter of high precision.  
      Furthermore, the solid-state imaging device may generate color signals of a first color system from N-types of electric signals generated from light received by the N photodiodes, based on an M (M being a natural number) by N matrix for converting a column vector whose compositional elements are N types of electric signals, into a column vector whose compositional elements are M types of color signals of the first color system.  
      According to the stated structure, color signals can be generated from electric signals generated by simply gathering electric charge born from light in a specific wavelength range, rather than from electric signals such as the three primary color signals of red, green and blue that are generated from light obtained using color filters. Therefore, colors can be realized without relying on color filters.  
      Furthermore, the solid-state imaging device may apply color correction to the color signals of the first color system, based on an M by M matrix for correcting the column vector whose compositional elements are the color signals of the first color system.  
      According to the stated structure, even if the generated color signal deviates from the desired color, the desired color can be reproduced by correcting the color signal.  
      Furthermore, the solid-state imaging device may convert the color signals of the first color system into color signals of a second color system, based on an L (L being a natural number) by M matrix for converting the column vector whose compositional elements are color signals of the first color system into a column vector whose compositional elements are color signals of the second color system.  
      According to the stated structure, even if generated color signals are of a color system that is different to the desired color system of color signal, color signals of the desired color system can be generated based on the color signal of the different color system, and therefore the desired color system can be reproduced.  
      Furthermore, the solid-state imaging device may apply color correction to the color signals of the second color system, the color correction being based on an L by L matrix for correcting a column vector whose compositional elements are color signals of the second color system.  
      According to the stated structure, even if the converted color signal deviates from the desired color, the desired color can be reproduced by correcting the converted color signal.  
      Furthermore, each photodiode may have a plurality of the apertures are provided thereabove.  
      According to the stated structure, the amount of light able to be received by each photodiode below each plurality of apertures can be increased. Therefore, the sensitivity of the photodiodes can be increased considerably, and high picture quality can be achieved.  
      Furthermore, the plurality of apertures provided above each photodiode may consist of (i) one or more apertures that enable light below the predetermined wavelength to pass through, and (ii) one or more apertures that enable light below a different predetermined wavelength to pass through.  
      According to the stated structure, a plurality of apertures enable light below the predetermined wavelength to pass, and the spectral characteristics of light in a vicinity of a maximum wavelength of light that one photodiode is able to receive can be finely adjusted.  
      Consequently, the spectral characteristics in the vicinity of the maximum wavelength that each photodiode receives are able to be adjusted with a plurality of types of maximum wavelengths, and the photodiodes are able to receive light of the desired wavelength.  
      Furthermore, the apertures may be arranged so that lengthwise directions of the aperture are parallel with each other, an interval between each aperture being less than or equal to a length direction dimension of the apertures.  
      According to the stated structure, the number of apertures in each pixel is increased. Therefore, the area occupied by apertures increases and sensitivity also increases.  
      Furthermore, the apertures may arranged so that lengthwise directions of the aperture are parallel with each other, an interval between each aperture being greater than or equal to a length direction dimension of the apertures.  
      According to the stated structure, light of a wavelength that is longer than light allowed to pass through the apertures can be prevented from passing through.  
      Furthermore, the solid-state imaging device may further include: a plurality of microlenses, each of which is provided with respect to a different one of the photodiodes and covers the aperture above the respective photodiode.  
      According to the stated structure, not only light in the apertures, but also light above the light shield film is focused in the apertures. Therefore, a greater amount of light can be received by the photodiodes, and high-sensitivity can be achieved. Furthermore, by adjusting the size of the microlenses, the amount of light that is received by each photodiode can be adjusted according to the performance required from the diode.  
      Furthermore, the solid-state imaging device may further include: a plurality of microlenses, each of which covers a different one or more of the apertures.  
      According to the stated structure, the light-collecting rate of the apertures can be improved considerably, and high-sensitivity can be achieved. Furthermore, the amount of light can be adjusted individually for each aperture, and individually for each wavelength.  
      Furthermore, the insulating film may be of a thickness that is equal to or greater than a minimum dimension of the apertures, and equal to or less than a maximum wavelength of light to be converted by the photodiodes.  
      According to the stated structure, the effect of light of a wavelength that attenuates before reaching the photodiodes (in particular, light close to the maximum wavelength) can be reduced, even in the light that passes through the apertures. This achieves high picture quality with little mixing of colors.  
      Furthermore, each aperture may be one of rectangular and circular in shape, and the dimension defined according to the predetermined wavelength may be a long side of the aperture if the aperture is rectangular, and a diameter of the aperture if the aperture is circular.  
      According to the stated structure, the dimensions of the apertures can be easily specified.  
      Furthermore, the predetermined wavelength may be a wavelength of one of near infrared light, red light, green light, and blue light in a medium formed over the aperture.  
      According to the stated structure, three or more types of spectral signals having respectively different predetermined wavelengths can be achieved, and the three primary colors can be realized. Therefore, colors can be realized without relying on an infrared filter and color filters.  
      Furthermore, the apertures may have a long, narrow rectangular shape, and be arranged such that a lengthwise direction of each aperture is oriented in a same direction.  
      According to the stated structure, a polarized component of light having an electric field in the lengthwise direction can be gathered in the photodiodes. Therefore, false signals caused by diffused reflection are prevented. Furthermore, only light of a predetermined polarized component is able to be received by the photodiodes, and prevention of mixing of color signals, and polarization accuracy are improved. As a result, high picture quality can be achieved.  
      Furthermore, the apertures may have a long, narrow rectangular shape, a plurality of apertures is provided with respect to each photodiode, and be arranged such that a lengthwise direction of the apertures for each photodiode is oriented in one of (i) a first direction and (ii) a second direction that is orthogonal to the first direction.  
      According to the stated structure, the polarized component of light can be separated according to pixel. Therefore, false signals caused by diffused reflection can be prevented, and the photodiodes receive only the desired polarized light. As a result, mixing of color signals is prevented, polarization accuracy is heightened, and high picture quality can be achieved.  
      In order to solve the stated problems, the present invention is also a signal processing device that processes N (N being a natural number) types of electric signals output by a solid-state imaging device, the signal processing device including: a differential matrix holding unit operable to hold a differential matrix for converting a vector whose compositional elements are the N types of electric signals into a vector whose compositional elements are M (M being a natural number) types of color signals of a first color system by taking a difference between an electric signal in the N types of electric signals and a neighboring electric signal in the N types of electric signals; and a color signal generation unit operable to generate, from the N types of electric signals, color signals of the first color system, based on the differential matrix.  
      According to the stated structure, in the solid-state imaging device, color signals can be generated from electric signals simply generated by gathering electric charge born from light of a different wavelength, rather than the electric signals such as the three primary color signals of red, green and blue that are generated from light obtained using color filters. Therefore, colors can be realized without relying on color filters.  
      Furthermore, the signal processing device may further include: a correction matrix holding unit operable to hold a correction matrix for correcting the vector whose compositional elements are the color signals of the first color system; and a color signal correction unit operable to correct the color signals of the first color system, based on the correction matrix.  
      According to the stated structure, even if the color signals are generated from light of a color that deviates from the desired color, a color signal of the desired color can be reproduced by correcting the color signal.  
      Furthermore, the signal processing device may include: a color system conversion matrix holding unit operable to hold a color system conversion matrix for converting the vector whose compositional elements are the color signals of the first color system into a vector whose compositional elements are L (L being a natural number) types of color signals of a second color system; and a color system correction unit operable to correct, based on the correction matrix, the color signals of the second color system.  
      According to the stated structure, color signals of another color system can be generated from the generated color signals. Therefore, an image can be reproduced with colors of the desired color system.  
      Furthermore, the signal processing device may further include: a correction matrix holding unit operable to hold a correction matrix for correcting the vector whose compositional elements are the color signals of the second color system; and a color signal correction unit operable to correct the color signals of the second color system, based on the correction matrix.  
      According to the stated structure, even if a converted color signal is a color signal generated from light of a color that deviates from the desired color, a color signal of the desired color can be re-generated by correcting the color signal.  
      Furthermore, the present invention is a camera that includes a solid-state imaging device, the solid-state imaging device including: a plurality of photodiodes that each convert received light to an electric signal; and a light shield film having a plurality of apertures formed therein, and being provided above and isolated from the photodiodes by an insulating film sandwiched between the light shield film and the photodiodes, wherein the apertures enable light of a wavelength below the predetermined wavelength to pass through, and each of the photodiodes correspond respectively to pixels that are each a minimum unit of an image that is taken, and each of the photodiodes has a different one of the apertures provided thereabove.  
      According to the stated structure, the infrared filter can be omitted, or be provided but with considerably reduced precision in blocking infrared light, and the color filters can be omitted, or be provided but with considerably reduced precision of the spectral characteristics. As a result, the solid-state imaging device manufacturing process can be simplified, and yield of infrared ray cut filters and color filters can be improved considerably.  
      Consequently, the stated structure enables reduced solid-state imaging device manufacturing time, reduced cost, and improved yield.  
      As a result, a low-priced, high-performance camera can be provided.  
      Furthermore, the apertures may be made up of N (N being a natural number) different types of the apertures, the predetermined wavelength may be different for each type of aperture, the photodiodes are N in number, and each of the N photodiodes may have an aperture of a different one of the N types provided thereabove, and the solid-state imaging device may further include: a signal processing circuit that processes N types of electric signals generated from light received respectively by the N photodiodes provided above the apertures whose form and dimensions are defined based on the respective predetermined wavelength, and the signal processing device may generate, from the N types of electric signals, color signals of a first color system, based on a differential matrix for converting a vector whose compositional elements are the N types of electric signals into a vector whose compositional elements are M (M being a natural number) types of color signals of a first color system, by taking a difference between an electric signal in the N types of electric signals and a neighboring electric signal in the N types of electric signals.  
      According to the stated structure, the wavelength cut off by the apertures can be changed if the shape and dimensions of the apertures are changed. This enables electric charge of different wavelength ranges to be gathered. For example, the combination of color filters and apertures enables light to be restricted for each color of color filter, even if the precision of spectral characteristics of the color filters is eased. Furthermore, color signals can be generated from electric signals generated by simply gathering electric charge of differing wavelengths, rather than from electric signals such as three primary color signals of red, green and blue. Therefore, colors can be realized without relying on color filters.  
      Furthermore, the camera may further include a signal processing apparatus that processes N (N being a natural number) types of electric signals output by the solid-state imaging device, wherein, in the solid-state imaging device, the apertures are made up of N different types of the apertures, the predetermined wavelength is different for each type of aperture, the photodiodes are N in number, and each of the N photodiodes has apertures of a different one of the N types provided thereabove, the solid-state imaging device outputs to the signal processing device, N types of electric signals generated from light received respectively by the N photodiodes provided above the apertures whose shape and dimensions are defined based on the respective predetermined wavelength, and the signal processing device generates, from the N types of electric signals, color signals of a first color system, based on a differential matrix for converting a vector whose compositional elements are the N types of electric signals into a vector whose compositional elements are M (M being a natural number) types of color signals of a first color system, by taking a difference between an electric signal in the N types of electric signals and a neighboring electric signal in the N types of electric signals.  
      According to the stated structure, the described effects can be obtained in a camera with a single sensor device in which the solid-state imaging device and the signal processing devices are incorporated.  
      Furthermore, the camera may further include: at least one more of the solid-state imaging device, the solid-state imaging devices totaling N in number, and in each solid-state imaging device, the apertures being made up of N (N being a natural number) different types of the apertures, the predetermined wavelength being different for each type of aperture, the photodiodes which being N in number, and each of the N photodiodes having apertures of a different one of the N types provided thereabove; and a signal processing device that processes N types of electric signals output by the solid-state imaging device, wherein the solid-state imaging device outputs to the signal processing device, N types of electric signals generated from light received respectively by the N photodiodes provided above the apertures whose shape and dimensions are defined based on the respective predetermined wavelength, and the signal processing device generates, from the N types of electric signals, color signals of a first color system, based on a differential matrix for converting a vector whose compositional elements are the N types of electric signals into a vector whose compositional elements are M (M being a natural number) types of color signals of a first color system, by taking a difference between an electric signal in the N types of electric signals and a neighboring electric signal in the N types of electric signals.  
      According to the stated structure, the described effects can be obtained in a camera with multi sensor devices in which a plurality of the solid-state imaging devices and the signal processing devices are incorporated.  
      Furthermore, the present invention is a spectral device including a spectral unit, wherein the spectral unit includes a opaque member that is provided non-parallel to a path of light from a light source and that has an aperture in a position where the path intersects with the opaque member, the aperture enabling light of a wavelength below a predetermined wavelength passes through.  
      According to the stated structure, the apertures provided in the opaque member function as high pass filters, and enable light below the predetermined wavelength to pass through. Therefore, the maximum value of the wavelength of incident light can be easily measured by checking which aperture the incident light passed through.  
      In addition, the types of frequency into which light is separated can be increased by adjusting the size of the apertures and changing the angle of the opaque member.  
      Furthermore, by adjusting the number of apertures, the amount of light that passes through can be easily adjusted. Therefore, the SN ratio of light can be improved in the spectral device.  
      Furthermore, the spectral device may further include a light detection unit operable to convert light separated by the spectral unit into an electric signal, according to intensity of the light.  
      According to the stated structure, light that passes through apertures can be changed into electrical signals. Therefore, an amount of light less than the predetermined wavelength can be detected.  
      Furthermore, the spectral device may further include a differential matrix holding unit and a signal processing unit, wherein the differential matrix holding unit is operable to hold a differential matrix for converting a vector whose compositional elements are N (N being a natural number) types of electric signals converted by the light detection unit, into a vector whose compositional elements are M (M being a natural number) types of color signals of a first color system by taking a difference between an electric signal in the N types of electric signals and a neighboring electric signal in the N types of electric signals; and the signal processing unit is operable to generate, from the N types of electric signals, M types of electric signals.  
      According to the stated structure, a set matrix operation is performed on the electric signals found from the light that passed through the apertures, and the intensity of light of a specific wavelength can be calculated. Therefore, a device that detects the dependence of wavelength on intensity can be easily fabricated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate a specific embodiment of the invention.  
      In the drawings:  
       FIG. 1  is a perspective drawing schematically showing a digital camera and a solid-state imaging device used therein;  
       FIG. 2A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the first embodiment, and  FIG. 2B  shows a cross section A-A′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 3  shows a list of refractive indexes of principal materials of the solid-state imaging device;  
       FIG. 4  is a graph showing spectral characteristics of the solid-state imaging device of the first embodiment;  
       FIG. 5A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the second embodiment, and  FIG. 5B  shows a cross section B-B′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 6  is a graph showing spectral characteristics of the solid-state imaging device of the second embodiment;  
       FIG. 7A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the third embodiment, and  FIG. 7B  shows a cross section C-C′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 8A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the fourth embodiment, and  FIG. 8B  shows a cross section D-D′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 9  is a graph showing spectral characteristics of the solid-state imaging device of the fourth embodiment;  
       FIG. 10A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the fifth embodiment, and  FIG. 10B  shows a cross section E-E′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 11  is a functional block diagram showing the structure of the solid-state imaging device of the sixth embodiment;  
       FIG. 12A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the sixth embodiment, and  FIG. 12B  shows a cross section F-F′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 13  is a graph showing spectral characteristics that deviate considerably from the ideal spectral characteristics;  
       FIG. 14A  is an upper surface view of a photoelectric conversion unit in a solid-state imaging device of the seventh embodiment, and  FIG. 14B  shows a cross section G-G′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 15A  is an upper surface view of a photoelectric conversion unit in a conventional solid-state imaging device, and  FIG. 15B  shows a cross section J-J′ of the photoelectric conversion unit viewed toward an arrow direction;  
       FIG. 16  is a graph showing spectral sensitivity characteristics of a photodiode and sensitivity characteristics of the human eye;  
       FIG. 17A  shows an example of the structure of a spectral device that spectrally separates one type of light, and  FIG. 17B  shows an example of a spectral device that spectrally separates into a plurality of types of light; and  
       FIG. 18  shows an example of the structure of a spectral device that uses a prism. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     First Embodiment  
      The following describes a first embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the Description of the Related Art have the same numbering thereas, and are omitted from the following description. Furthermore, the embodiments are based on a premise that, roughly speaking, infrared rays (IR) are light of 780 nm to 3 μm, red light (R) is light in the vicinity of 610 nm, green light (G) is light in the vicinity of 540 nm, and blue light (B) is light in the vicinity of 450 nm.  
      Outline of the First Embodiment  
       FIG. 1  is a perspective drawing schematically showing a digital camera and a solid-state imaging device used therein.  
      As can be seen from  FIG. 1 , a solid-state imaging device  101  used in a digital camera  100  is the same as the conventional solid-state imaging device in that light incident on the solid-state imaging device (hereinafter called “incident light”) via sealing glass that protects a photoreceptive surface is photoelectric converted to electrons by a photoelectric conversion unit (the area indicated by dots in the drawing).  
      The solid-state imaging device  101  differs from the conventional device in that instead of being provided with the infrared ray cut filter  18 , infrared light is cut off by the apertures  15  having a reduced size. This structure is based on a concept of having the apertures  15  function as high pass filters in the manner of a waveguide that cuts off electromagnetic waves exceeding a wavelength corresponding to the dimensions of the long side of the aperture  15  (hereinafter, also called “long side dimension”).  
      Waveguide  
      The following describes a waveguide that is representative of microwave transmission lines. Note that microwaves and light are both electromagnetic waves that satisfy Maxwell&#39;s equation.  
      A waveguide is a pipe whose walls are made of a highly conductive material such as copper. Waveguides are classified as rectangular, elliptical and so on, according to their cross-sectional shape. Note that it is commonly known that waveguides have a cutoff frequency determined by the structural dimensions of the cross section, and are unable to transmit signals below the cutoff frequency.  
      Taking for example a rectangular waveguide having a width a and a height b, the cutoff frequency f c  of the waveguide is shown by the following Equation (1). Furthermore, the wavelength λ c  corresponding to the cutoff frequency (hereinafter called “cutoff wavelength”) is shown by the following Equation (2). Here, the height b is assumed to be greater than the width a. In an elliptical waveguide having a radius r, the cutoff frequency f c  is shown by the following Equation (3), and the cutoff wavelength λ c  is shown by the following Equation (4). Note that it is assumed that the waveguide is filled with an isotropic, homogenous medium having a permittivity ε and a permeability μ. A velocity v of plane waves in the medium is shown by the following Equation (5).  
               f   c     =     v     2   ⁢   a               (   1   )             
 λ c =2a  (2)  
               f   c     =     v     3.413   ⁢   r               (   3   )             
 λ c =3.413r  (4)  
             v   =     1       ɛ   ⁢           ⁢   μ                 (   5   )             
 
      The following describes the solid-state imaging device of the first embodiment in view of the stated features.  
      Structure of the Solid-State Imaging Device of the First Embodiment  
       FIG. 2A  shows the photoelectric conversion unit of the solid-state imaging device of the first embodiment as viewed from above, and  FIG. 2B  shows a cross section A-A′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  110  is shown.  
      As can be seen from  FIGS. 2A and 2B , the light shield film  114  in the photoelectric conversion unit  110  is formed with apertures  115  therein. Each aperture  115  is located below a color filter  17   r ,  17   g  or  17   b , with the insulating film  16  therebetween. The infrared ray cut filter  18  that is provided above the color filters  17   r ,  17   g , and  17   b  in the conventional photoelectric conversion unit  10  is omitted in the photoelectric conversion unit  110 .  
      Each photodiode  12 , on receiving light, generates electrons and positive holes according to light received in a vicinity of a PN junction boundary, and efficiently converts the received light into current, based on the generated electrons and positive holes. The sensitivity of the photodiodes varies according the wavelength of the light, and the shorter the wavelength, the shallower from the surface the position where light is effectively absorbed. Note that electrons and positive holes generated in a position removed from the PN junction do not contribute to current generation because they re-bond and dissipate before reaching the depletion layer.  
      For this reason, when making a photodiode that is sensitive to long wavelengths, it is necessary to form a deep PN junction, and when making a photodiode that is sensitive to short wavelengths, it is necessary to form a PN junction close to the silicon surface.  
      As one example, in the following the photodiodes  12  are assumed to be photodiodes sensitive to light of a wavelength of 270 nm to 1000 nm, with sensitivity peaking at 700 nm to 800 nm. Furthermore, the insulating films  13  and  16  are made of silicon oxide (SiO 2 ) or silicon nitride (Si 3 N 4 ), and the light shield film  114  is made of aluminium (Al) or tungsten silicide (W—Si).  
      Dimensions of the Apertures  
      The apertures  115  have smaller dimensions that the apertures  15 , and cut off light of a wavelength exceeding the cutoff wavelength λ c  defined by the dimensions and shape of each aperture  115 . When light of a wavelength λ i  is incident to the aperture  115  via the insulating film  16  having a refractive index N r , the wavelength λ r  of the light in the insulating film  16 , taking into account the refractive index of the insulating film  16 , is shown by the following Equation (6).  
               λ   r     =       λ   i       N   r               (   6   )             
 
       FIG. 3  shows a list of refractive indexes of principal materials of the solid-state imaging device.  
      As can be seen from  FIG. 3 , a list  130  shows materials in column  131  and the respective refractive indexes of the materials in column  132 .  
      If, for example, the insulating film  16  is silicon oxide (SiO 2 ) and light incident on the insulating film  16  has a wavelength of 780 nm (infrared rays), the wavelength of the light when incident on the aperture  115  via the insulating film  16  will be, based on the refractive index 1.46, 534.25 nm. Furthermore, if the cutoff wavelength λ c  of the aperture  115  is approximately 534.25 nm or less, light of 780 nm incident from an outside source will be cut off by the aperture  115 .  
      Here, based on the following Equation (7), if the shape of the aperture  115  is rectangular, light of 780 nm will be cut off if the long side length of the aperture is 267. 12 nm or less. Furthermore, if the aperture is elliptical in shape, based on the following Equation (8), light of 780 nm will be cut off is the radius r of the aperture is approximately 228.53 nm or less (a diameter of 457.07 nm).  
                 λ   c     2     =         λ   rc       2   ⁢   N       &gt;   a             (   7   )                   λ   c     3.413     =         λ   rc       3.413   ⁢   N       &gt;   r             (   8   )             
 
      In view of this, approximate dimensions of the aperture  115  that enable visible light to pass visible light but cut off light of infrared rays (780 nm) and greater can be defined based on a cutoff wavelength λ rc  that will be cut off, the refractive index N r  of the insulating film  16  formed above the aperture  115 , and the shape of the aperture  115 .  
      Hereinafter, “cutoff dimension” denotes dimensions of the aperture defined by the cutoff wavelength λ rc , the refractive index N r  of medium formed above the aperture, and the shape of the aperture that enable light of a predetermined wavelength and greater to be cut off by the aperture. Furthermore, if the shape of the aperture is rectangular, “cutoff dimension” denotes the long side length, and if the shape is elliptical, “cutoff dimension” denotes the radius.  
      In addition, a cutoff dimension that enables light of a red light wavelength (610 nm) and below to pass, but cut off light of infrared rays (780 nm) and greater, is referred to as an “infrared cutoff dimension”.  
      Note that the upper limit of the cutoff dimension is defined according to the maximum wavelength of the range of wavelengths to which a photodiode  12  is sensitive. The reason for this is that even if the dimension of aperture is greater than this upper limit, the photodiode  12  will simply receive light of a wavelength that it is unable to sense, and the result will be the same as if the light was not received at all.  
      For example, if the maximum wavelength is 1000 nm, the cutoff dimension of the aperture will be, based on the above Equation (7), approximately 342.46 nm if the aperture is rectangular, and approximately 200.68 nm if the aperture is elliptical (a diameter of approximately 401.36 nm). Based on these figures, as a rough guide, the cutoff dimension of the aperture  115  is approximately 500 nm. This is remarkably small compared to the conventional apertures  15 , which have dimensions of 1500 nm. Hereinafter, a cutoff dimension found in such a manner is referred to as a maximum cutoff dimension.  
      Spectral Characteristics of the Solid-State Imaging Device of the First Embodiment  
      The following describes spectral characteristics of the photoelectric conversion unit  110  having the stated structure.  
       FIG. 4  is a graph showing spectral characteristics of the solid-state imaging device of the first embodiment.  
      Note that the horizontal axis indicates wavelength, and the vertical axis indicates spectral sensitivity.  
      As shown  FIG. 4 , a curve  151  indicates spectral characteristics of light that is able to pass through the aperture  115 . For reference, a curve  152   r  indicates spectral characteristics of light that is able to pass through a red color filter  17   r , a curve  152   g  indicates spectral characteristics of light that is able to pass through a green color filter  17   g , and a curve  152   b  indicates spectral characteristics of light that is able to pass through a blue color filter  17   b.    
      Note that in order to show characteristics of the apertures formed in the light shield film  114 , the characteristics were measured with the color filters  17   r ,  17   g  and  17   b  removed.  
      As shown by the curve  151 , the aperture  115  cuts off light of 760 nm and above, and enables passage of light of approximately 750 nm to 760 nm and below, where sensitivity begins to occur.  
      The curve  152   r  shows that the color filter  17   r  enables passage of light of a wavelength in range of 520 nm to 750 nm (hereinafter called the “R cone”), but enables almost no passage of other light. In particular, the color filter  17   r  enables passage of light in the vicinity of red light, as indicated by the peak of the color filter  17   r  being in the vicinity of the wavelength of red (610 nm).  
      The curve  152   g  shows that the color filter  17   g  enables passage of light of a wavelength in range of 450 nm to 640 nm (hereinafter called the “G cone”), but enables almost no passage of other light. In particular, the color filter  17   g  enables passage of light in the vicinity of green light, as indicated by the peak of the color filter  17   g  being in the vicinity of the wavelength of green (540 nm).  
      The curve  152   b  shows that the color filter  17   b  enables passage of light of a wavelength in range of 370 nm to 570 nm (hereinafter called “B cone”), but enables almost no passage of other light. In particular, the color filter  17   b  enables passage of light in the vicinity of blue light, as indicated by the peak of the color filter  17   b  being in the vicinity of the wavelength of blue (450 nm).  
      Summary of the First Embodiment  
      As described, the combination of the color filters  17   r ,  17   g  and  17   b  and the apertures  115  in the photoelectric conversion unit  110  enables visible light from incident light to pass through, while cutting off infrared light in the incident light. This means that light beyond the R cone that is incident on the filter  17   r  is cut off even without the infrared ray cut filter  18 .  
      Note that in reality the dimensions of the aperture are defined based on approximate cutoff dimensions, by numerical analysis using the FDTD (finite difference time domain) method and experiments such as spectral measuring. However, since the apertures can only be manufactured based on a set unit of measurement, the dimensions of the aperture vary slightly.  
      Other Remarks Regarding the First Embodiment  
      Although an example of light of 780 nm is used here, in reality the cutoff wavelength λ rc  to be cut off from light is defined according to purpose. For example, by designing the photoelectric conversion unit  110  to be sensitive to color signals generated by the solid-state imaging device, the photoelectric conversion unit  110  may be made to receive some infrared rays, with the cutoff wavelength λ rc  being set to cut off light of, for example, 790 nm or 800 nm. In particular, in an infrared camera it is important to receive light in the infrared range, and therefore the cutoff wavelength λ rc  may be set so that light in the infrared range of approximately 1000 nm can be received.  
      Note that red (R), green (G) and blue (B) may be the three types of monochromatic light that are the primary colors in the CIE (Centre Internationale d&#39;Eclairage) RGB color system, specifically: 700 nm (R), 546.1 nm (G) and 435.8 nm (B).  
      The solid-state imaging device  101  may be an MOS (metal oxide semiconductor) solid-state imaging device, an interline transfer CCD (charge coupled device) solid-state imaging device, or a frame transfer CCD solid-state imaging device.  
      The apertures may be elliptical in shape instead of square or rectangular.  
      In consideration of the influence of evanescent waves from the light shield film, the thickness of the insulating film  13  may be set at approximately the maximum wavelength in the range of waves to which the photodiode  12  is sensitive.  
     Second Embodiment  
      The following describes a second embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the first embodiment have the same numbering thereas, and are omitted from the following description.  
      Outline of the Second Embodiment  
      While the main object of the first embodiment is cutting off infrared rays, the second embodiment aims to further cut off light of unnecessary wavelengths by color.  
      The following describes the solid-state imaging device of the second embodiment in view of the described aim.  
      Structure of the Solid-State Imaging Device of the Second Embodiment  
       FIG. 5A  shows the photoelectric conversion unit of the solid-state imaging device of the second embodiment as viewed from above, and  FIG. 5B  shows a cross section B-B′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  210  is shown.  
      As shown in  FIGS. 5A and 5B , the light shield film  214  in the photoelectric conversion unit  210  is formed with apertures  215   r ,  215   g  and  215   b  therein, which differ from each other in dimension. The aperture  215   r  which has an infrared cutoff dimension is located below a color filter  217   r , the aperture  215   g  which has a red light cut off dimension is located below a color filter  217   g , and the aperture  215   b  which has a blue light cut off dimension is located below a color filter  217   b . The insulating film  16  is sandwiched between the apertures  215   r ,  215   g  and  215   b  and the color filters  217   r ,  217   g ,  217   b.    
      Here, a red light cutoff dimension indicates a cutoff dimension that will enable light of green light wave length (540 nm) and below to pass, but cut off light of red light wavelength (610 nm) and greater.  
      Furthermore, a green light cutoff dimension indicates a cutoff dimension that will enable light of blue light wave length (450 nm) and below to pass, but cut off light of green light wavelength (540 nm) and greater.  
      The infrared cutoff dimension is the largest among the dimensions, while the red light cutoff dimension is the second largest, and the green light cutoff dimension is the smallest.  
      Spectral Characteristics of the Solid-State Imaging Device of the Second Embodiment  
      The following describes spectral characteristics of the photoelectric conversion unit  210  having the stated structure.  
      Note that the precision of spectral characteristics of the color filters  217   r ,  217   g  and  217   b  is relatively low compared to the color filters  17   r ,  17   g  and  17   b.    
       FIG. 6  is a graph showing spectral characteristics of the solid-state imaging device of the second embodiment.  
      In  FIG. 6 , a curve  251   r  indicates spectral characteristics of light that is able to pass through the aperture  215   r , a curve  251   g  indicates spectral characteristics of light that is able to pass through the aperture  215   g , and a curve  215   b  indicates spectral characteristics of light that is able to pass through the aperture  215   b . For reference, a curve  252   r  indicates spectral characteristics of light that is able to pass through a red color filter  217   r , a curve  252   g  indicates spectral characteristics of light that is able to pass through a green color filter  217   g , and a curve  252   b  indicates spectral characteristics of light that is able to pass through a blue color filter  217   b.    
      Note that in order to show characteristics of the apertures formed in the light shield film  214 , the characteristics were measured with the color filters  217   r ,  217   g  and  217   b  removed.  
      As shown by the curve  251   r , the aperture  215   r  cuts off light of 760 nm and greater, and enables passage of light of approximately 750 nm to 760 nm and below, where sensitivity begins to occur.  
      As shown by the curve  251   g , the aperture  215   g  cuts off light of 650 nm and greater, and enables passage of light of approximately 630 nm to 640 nm and below, where sensitivity begins to occur.  
      As shown by the curve  251   b , the aperture  215   b  cuts off light of 580 nm and greater, and enables passage of light of approximately 570 nm to 580 nm and below, where sensitivity begins to occur.  
      The curve  252   r  shows that the color filter  217   r  enables passage of light of a wavelength in range of 520 nm to 750 nm (R cone), but enables almost no passage of light below 520 nm. In particular, the color filter  217   r  enables passage of light in the vicinity of red light, as indicated by the peak of the color filter  217   r  being in the vicinity of the wavelength of red (610 nm). It can also be seen that the color filter  217   r  enables passage of light with a longer wavelength than the long wavelength-side of the R cone.  
      The curve  252   g  shows that the color filter  217   g  enables passage of light of a wavelength in range of 450 nm to 630 nm (G cone), but enables almost no passage of below 450 nm. In particular, the color filter  217   g  enables passage of light in the vicinity of green light, as indicated by the peak of the color filter  217   g  being in the vicinity of the wavelength of green (540 nm). It can also be seen that the color filter  217   g  enables passage of light with a longer wavelength than the long wavelength-side of the G cone.  
      The curve  252   b  shows that the color filter  217   b  enables passage of light of a wavelength in range of 370 nm to 560 nm (B cone), but enables almost no passage of light below 370 nm. In particular, the color filter  217   b  enables passage of light in the vicinity of blue light, as indicated by the peak of the color filter  217   b  being in the vicinity of the wavelength of blue (450 nm). It can also be seen that the color filter  217   b  enables passage of light with a longer wavelength than the long wavelength-side of the B cone.  
      Summary of the Second Embodiment  
      As described, the apertures  215   r ,  215   g  and  215   b  function as high pass filters that cut off light that is unnecessary when reproducing light of the respective colors.  
      For example, the combination of the color filter  217   r  and the aperture  215   r  enables light in the vicinity of red light wavelength to pass, while cutting off light of infrared wavelength and greater. This means that, as shown by the curves  251   r  and  252   r , even if the wavelength range of incident light of the color filter  217   r  is longer than the wavelength of the R cone, light that exceeds 760 nm is cut off by the aperture  215   r . Furthermore, this enables spectral characteristics close to those shown by the curve  152   r  in  FIG. 4  to be achieved.  
      Similarly, as shown by the curves  251   g  and  252   g , the combination of the color filter  217   g  and the aperture  215   g  enables light in the vicinity of green light wavelength to pass, while cutting off light of red wavelength and greater. This enables spectral characteristics close to those shown by the curve  152   g  in  FIG. 4  to be-achieved.  
      Furthermore, as shown by the curves  251   b  and  252   b , the combination of the color filter  217   b  and the aperture  215   b  enables light in the vicinity of blue light wavelength to pass, while cutting off light of green wavelength and greater. This enables spectral characteristics close to those shown by the curve  152   b  in  FIG. 4  to be achieved.  
      Other Remarks Regarding the Second Embodiment  
      The apertures may be given differing shapes according to the color assigned to the pixel.  
     Third Embodiment  
      The following describes a third embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the second embodiment have the same numbering thereas, and are omitted from the following description.  
      Outline of the Third Embodiment  
      While the main object of the second embodiment is to cut off light of unnecessary wavelengths by color, the third embodiment aims to increase sensitivity, which is decreases due to the apertures being made smaller in order to cut off unnecessary light.  
      The following describes the solid-state imaging device of the third embodiment in view of the described aim.  
      Structure of the Solid-State Imaging Device of the Third Embodiment  
       FIG. 7A  shows the photoelectric conversion unit of the solid-state imaging device of the third embodiment as viewed from above, and  FIG. 7B  shows a cross section C-C′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  310  is shown.  
      As shown in  FIGS. 7A and 7B , the light shield film  314  in the photoelectric conversion unit  310  is formed with apertures  315   r ,  315   g  and  315   b , which differ from each other in dimension. The apertures  315   r  which have infrared cutoff dimensions are arranged with even intervals therebetween below the color filter  217   r . Similarly, the apertures  315   g  which have red cutoff dimensions are arranged even with intervals therebetween below the color filter  217   g , and the apertures  315   b  which have green cutoff dimensions are arranged even intervals therebetween below the color filter  217   b . The insulating film  16  is sandwiched between the apertures  315   r ,  315   g  and  315   b  and the color filters  217   r ,  217   g ,  217   b.    
      The drawing shows an example in which four apertures  315   r  are arranged with even intervals therebetween below the color filter  217   r , nine apertures  315   g  are arranged with even intervals therebetween below the color filter  217   g , and sixteen apertures  315   b  are arranged with even intervals therebetween below the color filter  217   b.    
      By reducing the distance between apertures, the number of apertures that can be provided in the pixel unit increases, thereby increasing area occupied by the apertures and, consequently, sensitivity. However, when the distance between the apertures is reduced, light of long wavelength passes through more easily. For this reason, if the distance between neighboring apertures is to be set with priority given to sensitivity, the apertures are formed in the light shield film  314  so that the distance therebetween is smaller than the corresponding cutoff dimension. On the other hand, if the distance between neighboring apertures is to be set so as to prevent mixing of light of long wavelength, the apertures are formed so that the distance therebetween is larger than the corresponding cutoff dimension. In other words, the distance between the apertures is determined according purpose.  
      Summary of the Third Embodiment  
      As described, by providing two or more apertures above each photodiode  12 , the amount of light able to be received by the photodiodes increases, and sensitivity increases considerably.  
      Other Remarks Regarding the Third Embodiment  
      Note that the thickness of the insulating film  13  may be set to be approximately the same as the infrared cutoff dimension if influence of attenuating light in the apertures  315   r  is to be reduced, or may be set to be approximately the same as the green cutoff dimension if influence of attenuating light in the apertures  315   b  is to be reduced.  
     Fourth Embodiment  
      The following describes a fourth embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the third embodiment have the same numbering thereas, and are omitted from the following description.  
      Outline of the Fourth Embodiment  
      While the main object of the third embodiment is to increase sensitivity which decreases due to the apertures being made smaller, the fourth embodiment aims to adjust spectral characteristics of light that passes through the apertures provided in each pixel, by forming apertures of at least two different cutoff dimensions in the light shield film belonging to each pixel.  
      The following describes the solid-state imaging device of the fourth embodiment in view of the described aim.  
      Structure of the Solid-State Imaging Device of the Fourth Embodiment  
       FIG. 8A  shows the photoelectric conversion unit of the solid-state imaging device of the fourth embodiment as viewed from above, and  FIG. 8B  shows a cross section D-D′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  410  is shown.  
      As shown in  FIGS. 8A and 8B , the light shield film  414  in the photoelectric conversion unit  410  is formed with respective combinations of apertures  415   r ,  415   g  and  415   b , which differ from each other in cutoff dimension, and apertures  416   r ,  416   g  and  416   b , which also differ from each other in cutoff dimension. The apertures  415   r  and the apertures  416   r  which have infrared cutoff dimensions are arranged with set intervals therebetween below the color filter  217   r . Similarly, the apertures  415   g  and the apertures  416   g  which have red cutoff dimensions are arranged with set intervals therebetween below the color filter  217   g , and the apertures  415   b  and the apertures  416   b  which have green cutoff dimensions are arranged with set intervals therebetween below the color filter  217   b . The insulating film  16  is sandwiched between the apertures  415   r ,  415   g ,  415   b ,  416   r ,  416   b  and  416   g  and the color filters  217   r ,  217   g ,  217   b.    
      The dimensions of the apertures are determined according to purpose. If the apertures  416   r  are to be set so as to give priority to sensitivity, they should be larger than the apertures  415   r . Furthermore, if the apertures  416   r  are to be set so as to prevent mixing of light of long wavelength, the apertures  416   r  should be smaller than the apertures  415   r . Similarly, the size of the apertures  416   g  can be determined according to purpose, based on the size of the apertures  415   g , and the size of the apertures  416   b  can be determined according to purpose, based on the size of the apertures  415   b.    
      For example, as shown in the drawing, two apertures  415   r , and two apertures  416   r  that are slightly smaller than the apertures  415   r  are provided below the color filter  217   r  at set intervals. Similarly, five apertures  415   g , and four apertures  416   g  that are slightly smaller than the apertures  415   g  are provided below the color filter  217   g  at set intervals. Furthermore, four apertures  415   b , and twelve apertures  416   b  that are slightly smaller than the apertures  415   b  are provided below the color filter  217   b  at set intervals.  
      Spectral Characteristics of the Solid-State Imaging Device of the Fourth Embodiment  
      The following describes spectral characteristics of the photoelectric conversion unit  410  having the stated structure.  
       FIG. 9  is a graph showing spectral characteristics of the solid-state imaging device of the fourth embodiment.  
      In  FIG. 9 , a curve  451   r  indicates spectral characteristics of light that is able to pass through the apertures  415   r  and  416   r , a curve  451   g  indicates spectral characteristics of light that is able to pass through the apertures  415   g  and  416   g , and a curve  451   b  indicates spectral characteristics of light that is able to pass through the apertures  415   b  and  416   b . For reference, the curves  152   r ,  152   g , and  152   b  shown in  FIG. 4  are shown in  FIG. 9  also.  
      Note that in order to show characteristics of the apertures formed in the light shield film  414 , the characteristics were measured with the color filters  217   r ,  217   g  and  217   b  removed.  
      As shown by the curve  451   r , the combination of the apertures  415   r  and  416   r  cuts off light of 760 nm and greater, and enables passage of light of approximately 750 nm to 760 nm and below, where sensitivity begins to occur, in a shape that follows the part of the curve of the long wavelength-side of the R cone.  
      As shown by the curve  451   g , the combination of the apertures  415   g  and  416   g  cuts off light of 650 nm and greater, and enables passage of light of approximately 630 nm to 640 nm and below, where sensitivity begins to occur, in a shape that follows the part of the curve of the long wavelength-side of the G cone.  
      As shown by the curve  451   b , the combination of the apertures  415   b  and  416   b  cuts off light of 580 nm and greater, and enables passage of light of approximately 570 nm to 580 nm and below, where sensitivity begins to occur, in a shape that follows the part of the curve of the long wavelength-side of the B cone.  
      Summary of the Fourth Embodiment  
      As described, the combination of the color filter  217   r , the apertures  415   r  and the apertures  416   r  enables light in the vicinity of red light wavelength to pass, while cutting off light of infrared wavelength and beyond. Furthermore, since the sensitivity and mixing of long wavelength light are adjusted according to the apertures  416   r , spectral characteristics close to those shown by the curve  152   r  in  FIG. 4  can be achieved.  
      Similarly, the combination of the color filter  217   g , the apertures  415   g  and the apertures  416   g  enables light in the vicinity of green light wavelength to pass, while cutting of light of red wavelength and beyond. Furthermore, since the sensitivity and mixing of long wavelength light are adjusted according to the apertures  416   g , spectral characteristics close to those shown by the curve  152   g  in  FIG. 4  can be achieved.  
      Furthermore, the combination of the color filter  217   b , the apertures  415   b  and the apertures  416   b  enables light in the vicinity of blue light wavelength to pass, while cutting off light of green wavelength and beyond. Furthermore, since the sensitivity and mixing of long wavelength light are adjusted according to the apertures  416   b , spectral characteristics close to those shown by the curve  152   b  in  FIG. 4  can be achieved.  
      Other Remarks Regarding the Fourth Embodiment  
      The dimensions of the each of the apertures  415   r  and  416   r  may be slightly smaller or slightly larger than the infrared ray cutoff dimensions. Similarly, the dimensions of the each of the apertures  415   g  and  416   g  may be slightly smaller or slightly larger than the red light cutoff dimensions, and the dimensions of the each of the apertures  415   b  and  416   b  may be slightly smaller or slightly larger than the green light cutoff dimensions.  
      Note that the thickness of the insulating film  13  may be set to be approximately the same as the infrared cutoff dimension if influence of attenuating light in the apertures  415   r  is to be reduced, or may be set to be approximately the same as the green cutoff dimension if influence of attenuating light in the apertures  416   b  is to be reduced.  
      Combinations of rectangular apertures having the same long side dimensions and elliptical apertures having the same diameters may be used. Alternatively, combinations of rectangular apertures having different long side dimensions and elliptical apertures having different diameters may be used.  
     Fifth Embodiment  
      The following describes a fifth embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the first embodiment have the same numbering thereas, and are omitted from the following description.  
      Outline of the Fifth Embodiment  
      While the first embodiment focuses on separating polarized components of incident light, the fifth embodiment aims to separate polarized components of incident light by forming the apertures in rectangular shapes, and varying the dimensions of the shorter sides thereof.  
      The following describes the solid-state imaging device of the fifth embodiment in view of the described aim.  
      Structure of the Solid-State Imaging Device of the Fifth Embodiment  
       FIG. 10A  shows the photoelectric conversion unit of the solid-state imaging device of the fifth embodiment as viewed from above, and  FIG. 10B  shows a cross section E-E′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  510  is shown.  
      As shown in  FIGS. 10A and 10B , long, narrow rectangular apertures  515  are formed in the light shield film  514  of the photoelectric conversion unit  510 .  
      Electromagnetic Waves in a Waveguide  
      The following describes electromagnetic waves in a rectangular waveguide, with the apertures  515  with long sides a and short sides b as the waveguide. Note that it is assumed that the walls of the rectangular waveguide are made of a perfect conductor, and that the waveguide is filled with an isotropic, homogenous medium having a permittivity ε and a permeability μ.  
      It is commonly known that electromagnetic waves propagated in rectangular waveguides are TE waves (transverse electric waves) or TM waves (transverse magnetic waves).  
      Here, TE waves (also called H waves) are electromagnetic waves of which the electric field of the propagation direction is zero, and TM waves (also called E waves) are electromagnetic waves of which the magnetic field of the propagation direction is zero.  
      The following describes TE waves and then TM waves. Here, a direction along the long sides a of the waveguide is called the x direction, a direction along the short sides b of the waveguide is called they direction, and a direction in which the TE waves or the TM waves are propagated in the waveguide is called the z direction. The electromagnetic field components in each direction are denoted as E x , E y , E z , H x , H y , and H z , the angular frequency is represented by ω, and the wave number in the z direction is represented γ.  
      TE Waves  
      When the electromagnetic waves propagated in the waveguide are TE waves, the magnetic field component H z  in the Z direction fulfills a wave equation shown by the following Equation (9).  
             {                   ∂   2     ⁢     H   z         ∂     x   2         +         ∂   2     ⁢     H   z         ∂     y   2         +       k   c   2     ⁢     H   z         =   0                 k   c   2     =         ω   2     ⁢   ɛ   ⁢           ⁢   μ     -     γ   2                       (   9   )               {               ∂     H   z         ∂   x       =   0           (       x   =   0     ,   a     )                   ∂     H   z         ∂   y       =   0           (       y   =   0     ,   b     )                   (   10   )               {             H   z     =       (       A   ⁢           ⁢   cos   ⁢           ⁢   α   ⁢           ⁢   x     +     B   ⁢           ⁢   sin   ⁢           ⁢   α   ⁢           ⁢   x       )     ⁢     (       C   ⁢           ⁢   cos   ⁢           ⁢   β   ⁢           ⁢   y     +     D   ⁢           ⁢   sin   ⁢           ⁢   β   ⁢           ⁢   y       )     ⁢     exp   ⁡     (       -   i     ⁢           ⁢   γ   ⁢           ⁢   z     )                       B   =   0     ,       sin   ⁢           ⁢   α   ⁢           ⁢   a     =   0                   D   =   0     ,       sin   ⁢           ⁢   β   ⁢           ⁢   b     =   0                   α   =       m   ⁢           ⁢   π     a       ,     β   =       n   ⁢           ⁢   π     b                       (   11   )             
 
      Furthermore, the electromagnetic field component in the cross section of the waveguide is shown by Equation (12). This is found from (H z ) of Equation (11), which is found by solving Equation (9) under Equation (10) which shows a boundary condition that the tangent component of the electric field must zero with respect to the perfectly conductive wall. Note that m and n are non-negative integers that are not zero simultaneously.  
             {             E   x     =     i   ⁢       ω   ⁢           ⁢   μ       k   c   2       ⁢       n   ⁢           ⁢   π     b     ⁢     H   0     ⁢   cos   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   sin   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       E   y     =       -   i     ⁢       ω   ⁢           ⁢   μ       k   c   2       ⁢       m   ⁢           ⁢   π     a     ⁢     H   0     ⁢   sin   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   cos   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       E   z     =   0                 H   x     =     i   ⁢     γ     k   c   2       ⁢       m   ⁢           ⁢   π     a     ⁢     H   0     ⁢   sin   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   cos   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       H   y     =     i   ⁢     γ     k   c   2       ⁢       n   ⁢           ⁢   π     b     ⁢     H   0     ⁢   cos   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   sin   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       H   z     =       H   0     ⁢   cos   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   cos   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                         (   12   )             
 
      Hereinafter, the eigen mode belonging to TE waves is called TE mode or H mode, and the eigen mode corresponding to m and n is called TE nm  mode or H nm  mode.  
      Here, eigen mode denotes the group of E x , E y , E z , H x , H y , and H z . Furthermore, the eigen value(or cutoff constant) with respect to the eigen mode is called k c .  
      TM Waves  
      When the electromagnetic waves propagated in the waveguide are TM waves, the electric field component E z  in the Z direction fulfills a wave equation shown by the following Equation (13).  
             {                   ∂   2     ⁢     E   z         ∂     x   2         +         ∂   2     ⁢     E   z         ∂     y   2         +       k   c   2     ⁢     E   z         =   0                 k   c   2     =         ω   2     ⁢   ɛ   ⁢           ⁢   μ     -     γ   2                       (   13   )             
 E z =0 (x=0, a or y=0, b)  (14)  
             {             E   z     =       (       A   ⁢           ⁢   cos   ⁢           ⁢   α   ⁢           ⁢   x     +     B   ⁢           ⁢   sin   ⁢           ⁢   α   ⁢           ⁢   x       )     ⁢     (       C   ⁢           ⁢   cos   ⁢           ⁢   β   ⁢           ⁢   y     +     D   ⁢           ⁢   sin   ⁢           ⁢   β   ⁢           ⁢   y       )     ⁢     exp   ⁡     (       -   i     ⁢           ⁢   γ   ⁢           ⁢   z     )                       A   =   0     ,       sin   ⁢           ⁢   α   ⁢           ⁢   a     =   0                   C   =   0     ,       sin   ⁢           ⁢   β   ⁢           ⁢   b     =   0                   α   =       m   ⁢           ⁢   π     a       ,     β   =       n   ⁢           ⁢   π     b                       (   15   )             
 
      Furthermore, the electromagnetic field component in the cross section of the waveguide is shown by Equation (16). This is found from (E z ) of Equation (15), which is found by solving Equation (13) under Equation (14) which shows a boundary condition that the electric field is zero at the perfectly conductive wall. Note that m and n are positive integers.  
             {             E   x     =       -   i     ⁢     γ     k   c   2       ⁢       m   ⁢           ⁢   π     a     ⁢     E   0     ⁢   cos   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   sin   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       E   y     =       -   i     ⁢     γ     k   c   2       ⁢       n   ⁢           ⁢   π     b     ⁢     E   0     ⁢   sin   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   cos   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       E   z     =       E   0     ⁢   sin   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   sin   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       H   x     =     i   ⁢       ω   ⁢           ⁢   ɛ       k   c   2       ⁢       n   ⁢           ⁢   π     b     ⁢     E   0     ⁢   sin   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   cos   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       H   y     =       -   i     ⁢       ω   ⁢           ⁢   ɛ       k   c   2       ⁢       m   ⁢           ⁢   π     a     ⁢     E   0     ⁢   cos   ⁢       m   ⁢           ⁢   π   ⁢           ⁢   x     a     ⁢   sin   ⁢       n   ⁢           ⁢   π   ⁢           ⁢   y     b     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       H   z     =   0                   (   16   )             
 
      Hereinafter, the eigen mode belonging to TM waves is called TM mode or E mode, and the eigen mode corresponding to m and n is called TM nm  mode or E nm  mode.  
      Transmission Characteristics of the Waveguide  
      The following described transmission characteristics of the waveguide.  
      The cutoff wavelength λ c(mn)  of the TE nm  mode and the TM nm  mode in the rectangular waveguide are shown by the following Equation (17). As shown by Equation (17), light that is below the cutoff wavelength λ c(mn)  defined for each eigen mode is able to pass through the apertures  515 . Consequently, the apertures  515  are considered to be multi-modal.  
      Here, multi-modal waveguide denotes a waveguide used in an area in which propagation is possible in a plurality of modes.  
               λ     c   ⁡     (   mn   )         =     2           (     m   a     )     2     +       (     n   b     )     2                   (   17   )             
 
      However, even if light of a higher mode passes through the apertures  515 , if the wavelength is below the shortest wavelength (270 nm) in the wavelength range to which the photodiode is sensitive, the light will not be sensed by the photodiode, and the result will be the same as if the light had not passed through the aperture  515  at all.  
      Here, higher mode denotes an eigen mode other than the eigen mode in which the cutoff wavelength is longest. The eigen mode in which the cutoff wavelength is longest is referred to as the dominant mode hereinafter.  
      In Equation (17), n and m are positive integers that are not zero simultaneously in the case of TE mode, and are positive integers in the case of TM mode. As shown by Equation (18), TE 10  is the dominant mode when a relationship a&gt;b is fulfilled by the long side a and the short side b. Furthermore, Equation (18) shows that light (electromagnetic waves) propagated in the waveguide in the dominant mode is limited to being components in one direction.  
             {             E   x     =   0                 E   y     =       -   i     ⁢       ω   ⁢           ⁢   μ       k   c   2       ⁢     π   a     ⁢     H   0     ⁢   sin   ⁢       π   ⁢           ⁢   x     a     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       E   z     =   0                 H   x     =     i   ⁢     γ     k   c   2       ⁢     π   a     ⁢     H   0     ⁢   sin   ⁢       π   ⁢           ⁢   x     a     ⁢   sin   ⁢       π   ⁢           ⁢   x     a     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                       H   y     =   0                 H   z     =       H   0     ⁢   cos   ⁢       π   ⁢           ⁢   x     a     ⁢     ⅇ       -   ⅈ     ⁢           ⁢   γ   ⁢           ⁢   z                         (   18   )             
 
      For this reason, in Equation (17), if the short side b is set so as to be less than the shortest wavelength of light able to pass through the aperture  515  in a first higher mode, the photodiode receives only light in the dominant mode, and therefore the waveguide can be considered to be a single-mode waveguide. In addition, polarized components of incident light can be separated.  
      Suppose, for example, that a relationship shown by Equation (19) using a coefficient is satisfied by the higher mode cutoff wavelength λ c(mn)  and the dominant mode cutoff wavelength λ c(10)  If a long side a of the rectangular waveguide is used, the dominant mode cutoff wavelength λ c(10)  is shown by the following Equation (20). Furthermore, if Equation (19) and Equation (20) are substituted in Equation (17), a relational equation shown by the following Equation (21) is derived between the short side b and the long side a of the rectangular waveguide. 
 
λ c(mn) =αλ c(10)   (19) 
 
λ c(10) =2a  (20) 
 
             b   =             n   2     ⁢     α   2         1   -       m   2     ⁢     α   2             ⁢   a             (   21   )             
 
      For example, in a case in which incident light below infrared rays (780 nm) from an external source passes through the aperture  515  via the insulating film  16 , taking into account the refractive index (N r =1.46), if λ c(10)  is 780 nm, λ c(11)  is 390 nm, and these are substituted in Equations (19) and (20) respectively, the aperture  515  functions as a single-mode waveguide in a range of at least 390 nm and less than 780 nm if the long side a of the aperture  515  is approximately 267.12 nm, and the short side b is less than approximately 154.22 nm. Furthermore, in a case in which incident light below red wavelength (610 nm) passes through the aperture  515 , the aperture  515  functions as a single-mode waveguide in a range of at least 390 nm and less than 610 nm, if the long side a of the aperture  515  is approximately 208.90 nm, and the short side b is less than approximately 173.70 nm. Similarly, in a case in which incident light below green wavelength (540 nm) passes through the aperture  515 , the aperture  515  functions as a single-mode waveguide in a range of at least 390 nm and less than 540 nm, if the long side a of the aperture  515  is approximately 184.93 nm, and the short side b is less than approximately 184.93 nm. In addition, in a case in which incident light below blue wavelength (450 nm) passes through the aperture  515 , the aperture  515  functions as a single-mode waveguide in a range of at least 390 nm and less than 450 nm, if the long side a of the aperture  515  is approximately 154.11 nm, and the short side b is less than approximately 154.11 nm.  
      Summary of the Fifth Embodiment  
      As described, the polarized components of light that has an electric field corresponding to the long side dimension of the aperture is collected in the photodiode  12  by forming the aperture with a long, narrow rectangular shape. This is because light having an electric field in the long side direction of the aperture generally passes through the aperture more easily than light having an electric field in the short side direction. This enables the polarized component of incident light to be separated according the short side dimension of the aperture, and consequently enables realization of high picture quality because false signals caused by diffused reflection of light are prevented and the photodiode  12  receives only desired polarized-light, and mixing of color signals is further prevented and polarization accuracy is heightened.  
      Other Remarks Regarding the Fifth Embodiment  
      Note that the apertures  515  may all have a same type of long side dimension, either an infrared ray cutoff dimension, a red light cutoff dimension, or a green light cutoff dimension. Alternatively, each type of pixel may be provided with a different one of three types of aperture  515 , each having different dimensions. As a result, in the photoelectric conversion unit  510 , selectivity of polarized light is improved and three types of color signal (the three primary colors) are generated, as in the photoelectric conversion unit  210  described in the second embodiment.  
      The light shield film  514  may be formed with two types of apertures therein which are arranged above the photodiode  12  such that respective long sides are oriented in different directions. This enables the photo-sensor  12  to receive light having different polarized components.  
      A plurality of apertures may be formed with respect to each aperture, as in the photoelectric conversion unit  310  described in the third embodiment.  
      Furthermore, a plurality of apertures of two different types may be formed, as in the photoelectric conversion unit  410  described in the third embodiment. Here, the short side dimension may be either the same or different for each aperture.  
     Sixth Embodiment  
      The following describes a sixth embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the second embodiment have the same numbering thereas, and are omitted from the following description.  
      Outline of the Sixth Embodiment  
      The main object of the second embodiment is to cut off light that is unnecessary when reproducing each of the colors from among the light that passes through the color filters  217   r ,  217   g  and  217   b  by using three types of apertures that have respectively different cutoff dimensions. In contrast, the sixth embodiment aims to generate RGB format signals necessary when reproducing each color, by applying signal processing to electric signals obtained by photoelectric converting light that has passed through three types of apertures that have respectively different cutoff dimensions. This is instead of the color filters  217   r ,  217   g  and  217   b  which are not present in the sixth embodiment.  
      The following describes the solid-state imaging device of the sixth embodiment in view of the described aim.  
      Solid-State Imaging Device of the Sixth Embodiment  
       FIG. 11  is a functional block diagram showing the structure of the solid-state imaging device of the sixth embodiment.  
      As shown in the figure, a solid-state imaging device  601  is composed of a photoelectric conversion unit  610 , a signal amplification unit  620 , an A/D conversion unit  630 , and a signal processing unit  640 .  
      The photoelectric conversion unit  610  is the photoelectric conversion unit  210  of the second embodiment from which the color filters have been omitted. The photoelectric conversion unit  610  outputs electric signals photoelectrically converted from light that has passed through the apertures of differing cutoff dimensions to the signal amplification unit  620 .  
       FIG. 12A  shows the photoelectric conversion unit of the solid-state imaging device of the sixth embodiment as viewed from above, and  FIG. 12B  shows a cross section F-F′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  610  is shown.  
      As shown in  FIGS. 12A and 12B , the photoelectric conversion unit  610  differs from the photoelectric conversion unit  210  in that the color filters  217   r ,  217   g  and  217   b  that are provided above the apertures  215   r ,  215   g  and  215   b  of differing cutoff dimensions with the insulating film  16  therebetween are omitted in the photoelectric conversion unit  610 . Note that it is possible to omit the insulating film  16  from the photoelectric conversion unit  610 .  
      In the following, L IC  represents an electrical signal generated according to photoelectric conversion by a photodiode above which an aperture having an infrared ray cutoff dimension is provided, L RC  represents an electrical signal generated according to photoelectric conversion by a photodiode above which an aperture having a red light cutoff dimension is provided, and L GC  represents an electrical signal generated according to photoelectric conversion by a photodiode above which an aperture having a green light cutoff dimension is provided. Furthermore, the signals output by the photoelectric conversion unit  610  to the signal amplification unit  620  are expressed as L IC , L RC , and L GC  respectively.  
      The signal amplification unit  620  is an amplifier that amplifies signals. The signal amplification unit  620  amplifies each signal output by the photoelectric conversion unit  610  (L IC , L RC , L GC ), and outputs each amplified signal to the A/D conversion unit  630 .  
      Here, the signal generated by amplifying L IC  is called AL IC , the signal generated by amplifying L RC  is called AL RC , and the signal generated by amplifying L GC  is called AL GC . Furthermore, the signals output by the signal amplification unit  620  to the A/D conversion unit  630  are expressed as AL IC , AL RC , and AL GC  respectively.  
      The A/D conversion unit  630  is an A/D converter that converts analog signals into digital signals. The A/D conversion unit  630  converts each signals output by the signal amplification unit  620  (AL IC , AL RC , AL GC ) into a digital signal and outputs each digital signal to the signal processing unit  640 .  
      Here, the digital signal generated by converting AL IC  is called DL IC , the digital signal generated by converting AL RC  is called DL RC , and the digital signal generated by converting AL GC  is called DL GC . Furthermore, the signals output by the A/D conversion unit  630  to the signal processing unit  640  are expressed as DL IC , DL RC , and DL GC  respectively.  
      The signal processing unit  640  is a DSP (digital signal processor) that processes digital signals. The signal processing unit  640  converts each digital signal output by the A/D conversion unit (DL IC , DL RC , DL GC ) into a red signal, a green signal, or a blue signal indicated by the RGB color system, and outputs each color signal.  
      Here, red, green, and blue signals indicated by the RGB color system and generated by converting DL IC , DL RC , and DL GC  according to differential processing, correction processing and the like are indicated by R, G, and B respectively. Furthermore, signals output by the signal processing unit  640  are expressed by R, G and B respectively.  
      Detailed Structure of the Signal Processing Unit  
      The signal processing unit  640  is composed of a differential matrix holding unit  641 , a color signal generation unit  642 , a correction matrix holding unit  643  and a color signal correction unit  644 .  
      The differential matrix holding unit  641  holds a matrix composed of differential coefficients (hereinafter called a “differential matrix”).  
      Here, each differential coefficient is a coefficient indicating that a color signal has been generated by taking a differential for one of the signals DL IC , DL RC  and DL GC .  
      The color signal generation unit  642  applies a matrix operation based on the differential matrix, thereby converting the signals input into the signal processing unit  640  (DL IC , DL RC , DL GC ) into color signals (R, G, B).  
      The correction matrix holding unit  643  holds a matrix composed of correction coefficients (hereinafter called a “correction matrix”).  
      Here, each correction coefficient indicates that color correction has been performed on one of the color signals (R, G, B).  
      The color signal correction unit  644  applies a matrix operation based on the correction matrix, thereby correcting each color signal that was converted by the color signal generation unit  642  (R, G, B) into an ideal color signal. Note that color correction is that which is used in color televisions, color photography and the like, and therefore details are not described here.  
      If the type of color signal in the RGB color system is expressed as M, and the type of signal input into the signal processing unit  640  is expressed as N, the differential matrix is shown by an M by N matrix, and the correction matrix is shown by an M by M matrix.  
      Differential Matrix Example  
      The following describes an example of the structure of the differential matrix. Note that it is assumed here that the following five conditions are fulfilled.  
      (1) Light received by the photodiodes is light standardized to specific wavelengths.  
      (2) The wavelength and the amount of the light differs according to the dimensions of the apertures provided above the photodiodes.  
      (3) The standardized light is obtained according to an additive process of red light, green light and blue light.  
      (4) Electric signals obtained by photoelectric conversion by the photodiodes are specified according to the wavelength of standardized light and amount of light received.  
      (5) Ultraviolet rays are attenuated by sealing glass or the like of the solid state image apparatus, and almost none are received by the photodiodes.  
      Furthermore, in the color signal generation unit  642 , a column vector made up of a color signal (R, G, B) indicated by the RGB color system, is obtained, as shown by the following Equation (22), by applying a differential matrix [D] held by the differential matrix holding unit  641  to a column vector made up of the signal input into the signal processing unit  640  (DL IC , DL RC , DL GC ).  
               [         R           G           B         ]     =       [           D   11           D   12           D   13               D   21           D   22           D   23               D   31           D   32           D   33           ]     ⁡     [           DL   IC               DL   RC               DL   GC           ]               (   22   )             
 
      Based on the stated five conditions, the column vector made up of the signal input into the signal processing unit  640  (DL IC , DL RC , DL GC ) is expressed, as shown by the following Equation (23), by applying a weight matrix [W] to the column vector made up of the color signal shown by the RGB color system (R, G, B). Note the element of each weight vector [W] is a positive value of at least 0 and no more than 1.  
               [           DL   IC               DL   RC               DL   GC           ]     =         [           W   11           W   12           W   13               W   21           W   22           W   23               W   31           W   32           W   33           ]     ⁡     [         R           G           B         ]       ⁢     
     ⁢           =       [           W   11           W   12           W   13             0         W   22           W   23             0       0         W   33           ]     ⁡     [         R           G           B         ]                 (   23   )             
 
      Here, it is assumed that an electric signal generated by photo-electric conversion by a photodiode above which an aperture of an infrared ray cutoff dimension is provided is not affected by infrared rays. Similarly, it is assumed that an electric signal generated by photo-electric conversion by a photodiode above which an aperture of a red light cutoff dimension is provided is not affected by red light. Furthermore, it is assumed that an electric signal generated by photo-electric conversion by a photodiode above which an aperture of a green light cutoff dimension is provided is not affected by green light. Further assuming that there is no weight for light that is not affected, W 21 , W 31 , and W 32  are 0.  
      Furthermore, if the above Equation (23) is solved with respect to a column vector made up of a color signal shown by the RGB color system (R, G, B), a differential matrix [D] shown by the following Equation (24) is obtained.  
               [           D   11           D   12           D   13               D   21           D   22           D   23               D   31           D   32           D   33           ]     =     [           1     W   11             -       W   12         W   11     ⁢     W   22                       W   12     ⁢     W   23       -       W   13     ⁢     W   22             W   11     ⁢     W   22     ⁢     W   33                 0         1     W   22             -       W   23         W   22     ⁢     W   33                   0       0         1     W   33             ]             (   24   )             
 
      Here, from the above Equation (24) D 11 , D 22  and D 33  are shown to be positive values, and D 12  and D 23  are shown to be negative values. Furthermore, D 21 , D 3 , and D 32  are shown to have a value 0.  
      Furthermore, when spectral characteristics close to the ideal spectral characteristics shown in  FIG. 6, 9  and so on are obtained, the weight of W 13  and W 23  is extremely low, and the value of D 13  is almost 0. Color signals shown by the RGB color system can be generated by taking only two signal differentials between the signals input into the signal processing unit  640  (DL IC , DL RC , DL GC ).  
       FIG. 13  is a graph showing spectral characteristics that deviate considerably from the ideal spectral characteristics.  
      As shown in  FIG. 13 , spectral characteristics of light that is able to pass through an aperture having an infrared ray cutoff dimension is indicated by a curve  651   r , spectral characteristics of light that is able to pass through an aperture having a red light cutoff dimension is indicated by a curve  651   g , and spectral characteristics of light that is able to pass through an aperture having a green curve cutoff dimension is indicated by a curve  651   b.    
      Spectral sensitivity indicated by curves  651   r ,  651   g  and  651   b  deviates considerably from that indicated by the curves in the second embodiment and the fourth embodiment.  
      However, as shown by the curves  651   r ,  651   g , and  651   b , when the spectral characteristics deviate considerably from those close to the ideal, the weight of W 13  and W 23  cannot be ignored, and the value of D 13  does not necessarily become 0. Furthermore, in this case, color signals shown by the RGB color system (R, G, B) become difficult to generate by taking differentials between only two signals, and the effect of other signals must be included.  
      As described, the differential matrix is composed of coefficients defined by factors such as the shape and dimensions of the apertures and the sensitivity of the photodiodes. Furthermore, if i is 1, 2, 3, etc., the components of a differential matrix (i, i) are indicated by positive values, and the components (i, i+1) of the differential matrix are indicated by negative values.  
      Summary of the Sixth Embodiment  
      As described, color signals are able to be obtained even in a solid-state imaging device from which color filters are omitted, according to photo-receivers above which apertures of differing cutoff dimensions are provided outputting signals corresponding to the respective cutoff dimension, and the signal processing unit  640  applying differential processing to the signal output by the photodiodes.  
      Other Remarks Regarding the Sixth Embodiment  
      Four colors, specifically, red (R), green (G), blue (B) and ultraviolet (UV) may be generated by providing a group of four photodiodes each having a different type of aperture (infrared ray cutoff dimension, red light cutoff dimension, green light cutoff dimension, blue light cutoff dimension, respectively) thereabove. Here, as shown by the following Equation (25), the signal processing unit  640  may apply differential processing to the four types of signals output by the photodiodes, and generate four color signal (R, G, B, UV). Note that here the differential matrix is a 4 by 4 matrix.  
      Here, the blue light cutoff dimension denotes a dimension that will enable light of ultraviolet rays (380 nm) or below to pass through, but that cuts off light of blue light wave length (450 nm) and greater.  
               [         R           G           B           UV         ]     =       [           D   11           D   12           D   13           D   14               D   21           D   22           D   23           D   24               D   31           D   32           D   33           D   34               D   41           D   42           D   43           D   44           ]     ⁡     [           DL   IC               DL   RC               DL   GC               DL   BC           ]               (   25   )             
 
      Furthermore, four colors, specifically, infrared (IR), red (R), green (G) and blue (B) may be generated by providing a group of four photodiodes each having a different type of aperture (maximum cutoff dimension, infrared ray cutoff dimension, red light cutoff dimension, green light cutoff dimension, respectively) thereabove. Here, as shown by the following Equation (26), the signal processing unit  640  may apply differential processing to the four types of signals output by the photoelectric conversion unit  610 , and generate four color signals (IR, R, G, B).  
               [         IR           R           G           B         ]     =       [           D   11           D   12           D   13           D   14               D   21           D   22           D   23           D   24               D   31           D   32           D   33           D   34               D   41           D   42           D   43           D   44           ]     ⁡     [           DL   LC               DL   IC               DL   RC               DL   GC           ]               (   26   )             
 
      Furthermore, five colors, specifically, infrared (IR), red (R), green (G), blue (B) and ultraviolet (UV) may be generated by providing a group of five photodiodes each having a different type of aperture (maximum cutoff dimension, infrared ray cutoff dimension, red light cutoff dimension, green light cutoff dimension, and blue light cutoff dimensions, respectively) thereabove. Here, as shown by the following Equation (27), the signal processing unit  640  may apply differential processing to the five types of signals output by the photoelectric conversion unit  610 , and generate five color signals (IR, R, G, B, UV).  
               [         IR           R           G           B           UV         ]     =       [           D   11           D   12           D   13           D   14           D   15               D   21           D   22           D   23           D   24           D   25               D   31           D   32           D   33           D   34           D   35               D   41           D   42           D   43           D   44           D   45               D   51           D   52           D   53           D   54           D   55           ]     ⁡     [           DL   LC               DL   IC               DL   RC               DL   GC               DL   BC           ]               (   27   )             
 
      In more general terms, m colors may be generated by proving a set of n photodiodes each having a different one of n types of aperture provided thereabove. Here, as shown by the following Equation (28), the signal processing unit  640  may apply differential processing the to n types of signals output by the photoelectric conversion unit  610 , and generate color signals of m colors. Note that here the differential matrix is an m by n matrix.  
               [           DC   1               DC   2             ⋮             DC     m   -   1                 DC   m           ]     =       [           D   11           D   12         ⋯         D       1   ⁢   n     -   1             D     1   ⁢   n                 D   21           D   22         ⋯         D       2   ⁢   n     -   1             D     2   ⁢   n               ⋮       ⋮       ⋰       ⋮       ⋮             D     m   -   11             D     m   -   12           ⋯         D     m   -     1   ⁢   n     -   1             D     m   -     1   ⁢   n                   D   m1           D   m2         ⋯         D     mn   -   1             D   mn           ]     ⁡     [           DL   1               DL   2             ⋮             DL     n   -   1                 DL   n           ]               (   28   )             
 
      Note that the color signals (R, G, B) generated by the color signal generation unit  642  may be further converted to complementary color signals (Cy, Mg, Y, G), as shown by the following Equation (29).  
               [                     Cy           Mg                 Ye                 G         ]     =       [         0       1       1           1       0       1           1       1       0           0       1       0         ]     ⁡     [               R           G                 B         ]               (   29   )             
 
      The solid-state imaging device  601  may be an element composed of one chip into which the photoelectric conversion unit  610 , the signal amplification unit  620 , the A/D conversion unit  630  and the signal processing unit  640  are integrated into one chip, or may be an element into which each of the photoelectric conversion unit  610 , the signal amplification unit  620 , the A/D conversion unit  630  and the signal processing unit  640  are integrated as separate chips.  
      Furthermore, a plurality of apertures may be provided for one photodiode as with the photoelectric conversion unit  310  of the third embodiment, or a plurality of two types of apertures may be provided as with the photoelectric conversion unit  410  of the fourth embodiment.  
      The differential matrix holding unit  641  may hold, in advance, a matrix that is a differential matrix multiplied by a correction matrix, and the color signals to which processing to color correction may be generated by the color signal generation unit  642 . Furthermore, the generated color signals may be output as is.  
     Seventh Embodiment  
      The following describes a seventh embodiment of the present invention with reference to the drawings. Note that structural elements having the same structure as those in the sixth embodiment have the same numbering thereas, and are omitted from the following description.  
      Outline of the Seventh Embodiment  
      The main object of the sixth embodiment is generate signals of RGB format that are necessary when reproducing each color without use of color filters  217   r ,  217   g  and  217   b , by applying signal processing to electric signals generated by the photoelectric conversion unit from light that passes through three types of apertures which have respectively different cutoff dimensions. In contrast, the seventh embodiment aims to enable more light to pass through the apertures.  
      The following describes the solid-state imaging device of the seventh embodiment in view of the described aim.  
      Solid-State Imaging Device of the Seventh Embodiment  
       FIG. 14A  shows the photoelectric conversion unit of the solid-state imaging device of the seventh embodiment as viewed from above, and  FIG. 14B  shows a cross section G-G′ of the photoelectric conversion unit viewed toward an arrow direction.  
      Note that for brevity, only one of the pixel units (two by two pixels) among the pixel units that make up the photoelectric conversion unit  710  is shown.  
      As shown in  FIGS. 13A and 13B , in the photoelectric conversion unit  710 , microlenses  719   r ,  719   g  and  719   b  are formed on the light shield film  214 , so as to cover the apertures  215   r ,  215   g  and  215   b , respectively.  
      Summary of the Seventh Embodiment  
      The microlenses formed on the light shield film  214  so as to cover the apertures cause light above the light shield film  214  to be focused into the apertures, thereby enabling the photodiode to receive a greater amount of light, and heightening sensitivity.  
      Other Remarks  
      If a plurality of apertures are formed with respect to each one photodiode as with the photoelectric conversion units  310  and  410  of the third and fourth embodiments, one microlens may be formed on the light shield film  214  so as to cover the plurality of apertures formed with respect to the one photodiode. Alternatively, a plurality of microlenses may be formed, each covering one or more of the apertures.  
      Note that the size of the microlenses may vary according the size of the apertures, or all lenses may be of a same size.  
     Eighth Embodiment  
      The following describes an eighth embodiment of the present invention with reference to the drawings.  
      Outline of the Eighth Embodiment  
       FIG. 18  shows an example of the structure of a conventional spectral device that uses a prism.  
      In a spectral device that uses a prism, incident light  1001  can be divided according to wave length by passing through a prism  1002 , because the refractive index of the prism  1002  varies according to wavelength.  
      For example, the wavelength of incident light  1001  is determined according to the positional coordinate  1005  at which light  1003  that passes through the prism  1002  hits a spectral display board  1004  that is placed apart from the prism. The incident light  1001  is red if light hits at a positional coordinate  1005 R of the spectral display board  1004 , green if light hits at a positional coordinate  1005 G of the spectral display board  1004 , and blue if light hits at a positional coordinate  1005 B of the spectral display board  1004 .  
      However, determining the wavelength of light accurately is difficult with this kind of spectral device because the positional coordinate  1005  of light that hits the spectral display board varies according to a number of factors such as the angle of the incident light  1001  to the prism  1002 , and the distance and angle between the prism  1002  and the spectral display board  1004 . Therefore, adjustment of this kind of spectral device requires fine operations to make adjustments in a number of places.  
      Consequently, the less places that need to be adjusted, the more convenient the spectral device.  
      Furthermore, it is preferable that operations for the spectral device be simple because it is necessary to finely set the frequency and amount of incident light to the photodiodes that make up the solid-state imaging device, to measure the photoelectric conversion characteristics of the photodiodes.  
      The spectral device of the present embodiment requires adjustment in less places, and simpler operations than a spectral device that uses a conventional prism.  
      Spectral Device of the Eight Embodiment  
       FIG. 17A  shows an example of the structure of a spectral device that spectrally separates one type of light.  FIG. 17B  shows an example of a spectral device that spectrally separates into a plurality of types of light.  
      When separating light into a plurality of types of light, a plurality of the spectral device of  FIG. 17A  are provided to make one spectral device (see  FIG. 17B ).  
      When incident light  1001  is incident on a spectral board  1010 , light less than a predetermined wavelength passes through an aperture  1013  provided in the spectral board  1010 .  
      The light  1030  that passes through aperture  1013  reaches a spectral display board  1012 .  
      If, for example, the aperture  1013  is a rectangular shape with a long side length of 230 nm, the light  1030  that passes through the aperture is light of a wavelength of blue light (in the vicinity of 450 nm) or less.  
      The relationship between the shape and dimension of the aperture and the frequency of the light that passes therethrough is the same as in the first embodiment.  
      Note that the spectral board  1010  may be made, for example, of aluminium (Al) or tungsten (W).  
      The following describes the spectral device of  FIG. 17B  that includes a light detection unit instead of the spectral display board  1012  of  FIG. 17A . This spectral device is called a spectral measurement device.  
      The spectral measurement device has apertures  1051 ,  1052  and  1053  of different dimensions provided in one spectral board, and light  1040  that passes through the apertures  1051 ,  1052  and  1053  reaches light detectors  1061 ,  1062  and  1063 , respectively, and is photoelectric converted.  
      Here, it is assumed that each aperture allows light of a different wavelength or less to pass through, and that the spectral characteristics of each aperture have been measured.  
      Light  1040  of which the spectral characteristics have been measured is incident on the apertures ( 1051 ,  1051  and  1053 ), and after passing through the apertures, is detected by the light detectors ( 1061 ,  1062  and  1063 ). The spectral characteristics of the light  1040  are found based on the correlation between the detected electric signals.  
      For example, the light that passes through the aperture  1051  is of a wavelength less than blue light, the light that passes through the aperture  1052  is of a wavelength less than green light, and the light that passes through the aperture  1053  is of a wavelength less than red light.  
      In this case, if the spectral characteristics of the light that passes through the aperture  1051  and the light that passes through the aperture  1052  and is of a wave length less than blue light are the same, the intensity of the wavelength range of green light can be found by subtracting the electric signal detected be the light detector  1061  from the electric signal detected by the light detector  1062 . Similarly, the intensity of the wavelength range of red light can be found by subtracting the electric signal detected be the light detector  1062  from the electric signal detected by the light detector  1063 .  
      In reality, apertures that enable spectral characteristics of light of a certain wavelength or less among light that passes through each of the apertures to be uniform is extremely difficult. For this reason, the intensity of necessary light can be found by performing a set matrix processing. Details of this matrix processing are as described in the sixth embodiment.  
      Other Remarks Regarding the Eighth Embodiment  
      (1) Although the spectral device of the present embodiment is provided with one spectral board having apertures therein, a different spectral board may be provided for each aperture.  
      Structuring the spectral device to have a plurality of spectral boards has an advantage of enabling fine adjustments. On the other hand, structuring the spectral device to have only one spectral board has an advantage of eliminating the need for positional adjustment between spectral boards to be omitted.  
      (2) In a spectral device that has a plurality of apertures and separates light into a plurality of lights, spectral separation boards  1011  are effective in preventing mixing of light that passes through apertures near each other.  
      (3) Although the spectral device of the present embodiment is provided with one aperture to enable light of a certain frequency and below to pass, a plurality of apertures of a same shape may be provided.  
      Furthermore, a plurality of apertures of different shapes may be provided.  
      Providing a plurality of apertures enable a greater amount of light to pass through the apertures, and improves the SN ratio of the spectral device or the spectral measurement device. This is as described in the third embodiment.  
      Furthermore, by combining apertures having different shapes, light having spectral characteristics close to the necessary characteristics can pass through. This is as described in the fourth embodiment.  
      (4) Although the apertures in the present embodiment are described as having a rectangular shape, they may have another shape such as a round shape or a slit shape.  
      Although the present invention has been fully described by way of examples with reference to accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.