JP2003258220A - Imaging element and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a suitable optical low-pass effect even at a peripheral part of an imaging element and to improve light condensing. <P>SOLUTION: The imaging element comprises a plurality of pixels arranged, and each has a photoelectric converter and a wavelength transmitting part for transmitting the light in a predetermined wavelength range to the converter. A wavelength selector has a structure which has a peak. In this element, the pixels are disposed on the periphery of the element, and each has the peak of the wavelength selector disposed in a central direction of the element from the center of the converter. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device for picking up a subject image.

[0002]

2. Description of the Related Art A conventional structure of a general image pickup device for forming a color image is shown in FIG. FIG. 21 is a central cross-sectional view of pixels that form the image sensor. Reference numeral 101 is a microlens which collects light rays from the outside and plays a role of increasing the light-trapping efficiency, and 102 is a color filter used for wavelength-separating the captured light rays.
A primary color filter of any one of (red) G (green) and B (blue) is provided. As a color filter, there is also a complementary color filter using three colors of C (cyan) M (magenta) Y (yellow). An imaging technique is widely used in which these pixels are arranged in a mosaic pattern and the subsequent signal processing produces luminance information and color information corresponding to the number of pixels. The color filter array of the image sensor used here often has a configuration called a Bayer array.

Reference numeral 104 is a silicon wafer, 103 is a photoelectric conversion portion having a function of converting received photons into electric charges, and 1
Reference numeral 10 is a Poly wiring layer which plays a role of a gate for controlling charges of the photoelectric conversion unit. Wiring layers 111 to 113 are made of metal such as aluminum.

[0004]

However, the above conventional example has the following problems. In general, imaging for obtaining good image characteristics includes a first process of forming an object image by an optical device, a second process of adjusting so as to suppress a high frequency component of the spatial frequency characteristic of the object image, and a spatial frequency characteristic. It comprises a third process for photoelectrically converting the adjusted object image, and a fourth process for correcting the response of the obtained electric signal according to the spatial frequency. At this time, since the optical image is sampled by the image sensor having a finite number of pixels, in order to obtain a high-quality image output, the spatial frequency characteristic of the optical image should be higher than the Nyquist frequency peculiar to the image sensor according to the sampling theorem. It is necessary to reduce the components of.
Here, the Nyquist frequency is half the sampling frequency determined by the pixel pitch. Therefore, the optimized series of processes adjusts the sampled optical image to an optical image having a characteristic according to the Nyquist frequency peculiar to the image sensor, so that aliasing distortion is not noticeable, that is, a high-quality image with no moire is noticeable. Is what you get.

MTF which is the spatial frequency transfer characteristic of an image
(Modulation Transfer Function) is an evaluation quantity that can well express the characteristics related to the sharpness of digital still cameras and video cameras. Specific elements that affect the MTF are an image forming optical system that is an optical device, an optical low-pass filter for band limitation of an object image, an aperture shape of a photoelectric conversion region of an image sensor, digital aperture correction, and the like.
The overall MTF representing the final image characteristics is given as the product of the MTF of each element. That is, the MTFs from the first process to the fourth process described above are respectively obtained, and the product thereof may be calculated.

However, since the fourth process, the digital filtering process, is performed on the image output already sampled by the image pickup device, it is not necessary to consider a high frequency exceeding the Nyquist frequency.

Therefore, the configuration for reducing the component of the spatial frequency characteristic of the optical image above the Nyquist frequency peculiar to the image pickup element is the M of the first process except the fourth process.
This means that the component above the Nyquist frequency is small in the product of TF, MTF of the second process, and MTF of the third process. Here, when viewing still images like a digital still camera, the resolution is better when the high frequency above the Nyquist frequency is not zero, but the response at a frequency slightly below the Nyquist frequency is high, even if some high frequencies remain. It is necessary to consider that it tends to give a pleasing image.

In the first process of forming an object image by the image forming optical system, it is generally easier to correct optical aberration in the center of the screen than in the periphery. In order to obtain a good image at the periphery of the screen, it is necessary to obtain extremely good characteristics near the diffraction limit MTF determined by the F number of the imaging lens at the center of the screen. In recent years, the number of pixels of image pickup devices has been reduced, and this need has been increasing. Therefore, it is advisable to consider the MTF on the assumption that the imaging optical system is an ideal lens having no aberration.

Further, in an image pickup device in which light receiving apertures of width d are spread without any gap, the width of the light receiving apertures matches the pixel pitch, so the response value of the third process at Nyquist frequency u = d / 2 is quite large. high. For this reason, it is common to trap near the Nyquist frequency in the second process in order to lower the total MTF near the Nyquist frequency.

In the second process, an optical low pass filter is usually used. A material having a birefringence characteristic such as quartz is used for the optical low pass filter. Also,
A phase type diffraction grating as disclosed in Japanese Patent Laid-Open No. 2000-066141 may be used.

By interposing a birefringent plate in the optical path of the optical device,
When the optical axis is tilted so as to be parallel to the horizontal direction of the image plane, the object image formed by the ordinary ray and the object image formed by the extraordinary ray are formed so as to be shifted in the horizontal direction by a predetermined amount. The trapping of a specific spatial frequency by the birefringent plate means that the bright part and the dark part of the fringe of the spatial frequency are shifted so as to overlap each other. The MTF by the optical low pass filter is expressed by the equation (1).

R ₂ (u) = | cos (π · u · ω) (1) where R ₂ (u) is the response, u is the spatial frequency of the optical image, and ω is the object image separation width. is there.

By properly selecting the thickness of the birefringent plate, the response can be zero at the Nyquist frequency of the image pickup device. When a diffraction grating is used, the same effect can be obtained by separating and superimposing an optical image into a plurality of images having a predetermined positional relationship by diffraction.

However, in order to manufacture a birefringent plate, it is necessary to grow crystals such as quartz and lithium niobate and then polish them thinly, which is very expensive. In addition, since the diffraction grating requires a highly precise fine structure, it is still expensive.

Next, considering the utilization efficiency of light rays, for example, in a CCD image pickup device in which pixels with primary color filters, which are said to have good color reproducibility, are arranged in a mosaic pattern, R (red) G (green) B (blue). The optical filters of 1) are arranged one by one between the microlens 2 and the photoelectric conversion region 3.

At this time, only red light is photoelectrically converted in the pixel provided with the red optical filter, and blue light and green light are absorbed by the optical filter to become heat. Similarly, in a pixel with a green optical filter, blue light and red light are not photoelectrically converted into heat, and in a pixel with a blue optical filter, green light and red light are not photoelectrically converted into heat. . That is, in each pixel of the conventional color image pickup device, only the light that has passed through the predetermined optical filter in the incident light flux is photoelectrically converted and output as an electric signal, so the light that cannot pass through the optical filter is converted into heat or the like. It has been abandoned.

FIG. 22 shows the spectral transmittance characteristics of the RGB color filters in the image sensor. Due to its high infrared transmittance, there is actually a further 650
Infrared cut filters that cut off wavelengths of nm and above are used in layers. As can be seen from this, only about 1/3 of visible light is effectively used in one pixel.

Considering the utilization efficiency for each color of RGB in more detail, for example, the RGB pixel area ratio of the color image pickup device of the Bayer array shown in FIG. 22 constitutes a regular array 1.
When the unit area is 1, it is 1/4: 2/4: 1/4. Therefore, when the total light quantity is 1, the utilization ratio of green light is the wavelength selectivity item and the area ratio item. 1/3 × 2 as product
/ 4 = 1/6, red light and blue light are 1/3 × 1/4 = 1 /
12, totaling 1/6 + 1/12 + 1/12 = 1/3
Therefore, the usage efficiency is 1/3. On the contrary, when the total amount of light is 1, green light is 2/3 × 2
/ 4 = 1/3 is 2/3 × 1/4 = 1 for red light and blue light
/ 6 will not be used effectively.

Although the image pickup device using the color filters of the primary colors has been described above, about 1/3 of visible light is not photoelectrically converted in the image pickup device using the complementary color filter and is effectively used. Not done. As described above, in both the primary color system and the complementary color system, the light utilization efficiency is low in the conventional single-plate type image pickup device because the image pickup surface is divided by the color filters.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to obtain an appropriate optical low-pass effect and to improve the utilization efficiency of incident light. It is to realize an image sensor.

[0021]

In order to solve the above-mentioned problems, an image pickup device in which a plurality of pixels including a photoelectric conversion unit and a wavelength selection unit for transmitting light in a predetermined wavelength range to the photoelectric conversion unit are arranged is provided. And the wavelength selection unit has a structure having vertices, and in the pixels located in the peripheral portion of the image pickup device, the vertices of the wavelength selection unit have a center of the image pickup device rather than a center of the photoelectric conversion unit. Provided is an imaging device characterized by being positioned in a direction.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) FIGS.
The first embodiment of the present invention is shown in FIG.

FIG. 1 is a sectional view of a central portion of an image sensor in which a plurality of pixels are arranged in a first direction and a direction orthogonal to the first direction.
FIG. 2 is a cross-sectional view of the peripheral portion of the image sensor, and FIG. 3 is a view of the image sensor from above. Here, FIG. 1 is a cross-sectional view of the shaded portion 21 of FIG. 3, and FIG. 2 is the shaded portion 2 of FIG.
It is sectional drawing of the 2 part.

1 and 2, 1 is a silicon wafer,
Reference numeral 2 is a microlens, 3 is a photoelectric conversion unit having a function of converting received photons into electric charges, 4 (4r, 4g) is a dichroic film which is a wavelength selection unit for wavelength separating the light flux, and 5 and 6 are respectively The first and second refractive index layers, 7 to 9 are first to third refractive index portions, and 10 is a Poly wiring layer which plays a role of a gate for controlling charges of the photoelectric conversion portion. 11
1 to 13 are wiring layers made of metal such as aluminum.
Reference numeral 1 is an AL1 wiring layer that plays a role of connection and output line between respective parts, 12 is an AL2 wiring layer that plays a role of well power supply line and control line, and 13 is an AL3 wiring layer that plays a role of light shielding and power supply line.

The microlens 2 has an upwardly convex spherical shape and has a positive lens power. Therefore, the light flux reaching the microlens 2 has a function of condensing on the photoelectric conversion unit 3. The first refractive index layer 5 is formed of a material having a low refractive index, and for example, magnesium fluoride (MgF ₂ ) having a refractive index of 1.38 can be used. Further, the second refractive index layer 6 sandwiched between the first refractive index layer 5 and the dichroic film 4 which is the wavelength selecting portion is formed of a material having a high refractive index, and for example, titanium dioxide having a refractive index of 2.5. (TiO ₂ )
Etc. can be used. By adopting such a configuration, the light flux traveling from the second refractive index layer 6 to the first refractive index layer 5 has the property of being easily totally reflected at the interface.

The second refractive index portion 8 is made of a high refractive index material such as titanium dioxide, and the third refractive index portion 9 is made of silicon dioxide (SiO ₂ ) or magnesium fluoride having a refractive index of 1.46. It is molded using a low refractive index material. As a result, the light beam incident on the second refractive index portion 8 is likely to be totally reflected at the interface with the third refractive index portion 9, and thus serves as a light guide path to the photoelectric conversion portion 3. Since the first refractive index portion 7 needs not to be totally reflected at the interface with the second refractive index portion 8, it is made of a material having the same refractive index as or lower than that of the second refractive index portion 8. Need to be molded. However, the second
Since it is desirable that the difference in the refractive index between the refractive index layer 6 and the refractive index layer 6 is not so large, for example, silicon nitride (S
iN) or the like can be used.

Generally, a dichroic film is formed by alternately stacking a substance having a high refractive index and a substance having a low refractive index with a film thickness that is an integral multiple of ¼ of a wavelength λ of interest. . By adopting such a structure, the wavelength of the transmitted light flux can be selected. An example of the film thickness of the dichroic film 4 used in this embodiment is shown in FIG. Titanium dioxide was used as the high refractive index material and silicon dioxide was used as the low refractive index material, and the film thickness and the number of layers were as shown in FIG. The transmission characteristics of this dichroic film 4 are shown in FIG. Figure 1
As can be seen from the characteristic diagram of 0, it has a characteristic close to that of a conventional color filter using a dye. Therefore, even if the dichroic film 4 of this configuration is used, the characteristics similar to those of the conventional image pickup device can be obtained. These laminated films can be easily formed by using PVD (Physical Vapor Deposition).

Here, one pixel 100 is composed of a silicon wafer 1, a microlens 2, a photoelectric conversion section 3, a wavelength selection section 4, first and second refractive index layers 5 and 6, and first to third refraction layers. Rate parts 7 to 9, Poly wiring layer, AL1 wiring layer 11, AL2
It is defined as being composed of the wiring layer 12 and the AL3 wiring layer 13. The boundary between pixels is indicated by 15.

The pixel shown in FIG. 2 is located at a position apart from the optical axis of the taking lens (not shown). Therefore, the center of the pupil of the imaging lens is located on the right side, and the light flux incident on the microlens 2 has an angle from the right direction. Therefore, the microlens 2 is arranged on the right side of the central axis 3c determined by the photoelectric conversion unit.

Further, the entire quadrangular pyramid forming the dichroic film 4 which is the wavelength selecting portion is shifted to the right. That is, the shape of the quadrangular pyramid is the same, that is, the left and right angles θ1 and θ2 of the slope of the quadrangular pyramid remain the same (θ1 = θ2), and the vertex 4
The dichroic film 4 which is a wavelength selection unit is arranged so that P is located on the right side. More specifically, in this structure, the chief ray M _L passing through the vertex 2c of the microlens is used.
The dichroic film 4P, which is the wavelength selection unit, is arranged so that its apex is located on the right side.

Contrary to FIG. 2, when the center of the pupil of the imaging lens is located on the left side, the apex 4P is located on the left side of the principal ray passing through the apex 2c of the microlens. The membrane 4 is arranged.

FIG. 4 is an explanatory view of a dichroic film which is a wavelength selection unit arranged in the image pickup device. What is shown around the image sensor of this figure is an enlarged view of the wavelength selection unit 4 at each position. In the peripheral portion of the image sensor, the vertex 4P of the dichroic film, which is the wavelength selection unit, does not change the shape of the dichroic film 4, which is the wavelength selection unit, and the vertex 4P of the wavelength selection unit is closer to the center of the image sensor than the central axis 3c determined by the photoelectric conversion unit. A dichroic film, which is a wavelength selection unit, is arranged so as to be located at. That is, θ1 = θ2 and the pixel boundary 15
And the bottom surface of the dichroic film 4, which is the wavelength selection unit, is displaced. In more detail, placing the dichroic film is the wavelength selection portion as a vertex 4P dichroic film is the wavelength selection portion in the center side of the image pickup device 500 than the main light beam M _L passing through the apex 2c of the microlenses is located is doing.

Next, the behavior of a light beam having a predetermined angle of view that is incident on the peripheral portion of the image sensor of this embodiment will be described.

FIG. 5 shows the behavior of the light beam which is transmitted through the dichroic film 4 which is the wavelength selection unit.
The light flux coming from the upper part of the figure enters the microlens 2 and is subjected to a condensing function. Next, the first refractive index layer 5 and the second refractive index layer 6 are sequentially incident to reach the dichroic film 4g. In the dichroic film 4 which is the wavelength selection unit, only the light flux having a predetermined wavelength is selectively transmitted and is incident on the first refractive index unit 7. Then, the light travels to the second refractive index section 8 and is guided to the photoelectric conversion section 3 by being subjected to the action of repeating total reflection at the interface between the second refractive index section 8 and the third refractive index section 9. Since the interface between the second refraction part 8 and the third refraction part 9 has a tapered shape in which the incident part is widened, it can be totally reflected even on the tapered surface and guided to the photoelectric conversion part 3.

Adjacent pixels 100 _ij r and 100
The behavior of the light flux is substantially the same for _{i + 1 and j} r.

FIG. 6 shows a pixel 100 _ij g which receives green light.
The behavior of only the light flux that is incident on the and reflected by the dichroic film 4g, that is, the light flux including the blue light and the red light is shown. The light flux emitted from the pupil of the imaging lens at a position far away from the size of the pixel passes through the infrared cut filter and becomes a light flux like the object light 120. The object light 120 coming from the upper part of the figure is incident on the microlens 2 and is condensed. Next, the first refractive index layer 5 and the second refractive index layer 6 are sequentially incident to reach the dichroic film 4g.
Here, due to the characteristics of the dichroic film 4g, light beams other than green are reflected. The dichroic film 4g is formed on a surface having a quadrangular pyramid shape. Since the formed dichroic film 4 is a quadrangular pyramid, the reflected light flux travels while changing its direction from the center to the outside. Then, the light reflected by the dichroic film 4g undergoes total reflection at the interface between the second refractive index layer 6 and the first refractive index layer 5 with a light flux having a critical angle or more. The light flux that is directed downward again is the element 100 _ij r and 100 that receives the red light that is the adjacent pixel.
Proceed towards _{i + 1, j} r. Dichroic film 4
The light flux that has passed through r advances in order to the first refractive index portion 7 and the second refractive index portion 8. Subsequently, the second refractive index portion 8 tries to proceed to the third refractive index portion 9, but as described above,
Since the second refractive index portion 8 has a higher refractive index than the third refractive index portion 9, a light beam having a critical angle or more is totally reflected at the interface. Since the interface between the second refractive index portion 8 and the third refractive index portion 9 has a tapered shape in which the incident portion is widened, the frontage for capturing the incident light flux is wide, and a large amount of the luminous flux is captured in the second refraction portion 8. Is able to. Since the interface near the photoelectric conversion unit 3 is formed by two surfaces that are substantially parallel to the vertical direction,
The light flux that has not entered the photoelectric conversion unit 3 due to the first total reflection is again totally reflected at the interface on the opposite side, and finally enters the photoelectric conversion unit 3.

[0037] In this structure, a wavelength selection portion as a vertex 4P dichroic film is the wavelength selection portion in the center side of the image pickup device 500 than the main light beam M _L passing through the apex 2c of the microlens is positioned dichroic film 4 are arranged. Therefore, the light beam reflected by the dichroic film 4, which is the wavelength selection unit, is evenly incident on the photoelectric conversion units of the adjacent pixels, so that an appropriate optical low-pass effect can be obtained.

As described above, in the central portion of the image pickup device, the center of the microlens 2 and the dichroic film 4 are provided.
And the center of the photoelectric conversion unit 3 coincide with each other in the direction perpendicular to the image sensor plane, and in the peripheral portion of the image sensor,
The apex of the dichroic film 4 is located closer to the center of the image sensor than the center of the photoelectric conversion section.

Therefore, in the image sensor of this embodiment,
It is possible to receive light efficiently.

Here, in the peripheral portion of the image pickup device of the above embodiment, the chief ray M passing through the vertex 2c of the microlens.
_It has been described that the dichroic film 4g, which is the wavelength selection unit, is arranged so that the apex of the dichroic film 4g is located on the right side of _L. However, as shown in FIG. 7, the chief ray M _L is located at the apex of the microlens 2 and the wavelength selection unit 4P. It may be configured to pass through the apex of.

In the case of the configuration of FIG. 7, as compared with the configuration of FIG. 2, the amount of light flux reflected by the wavelength selection unit 4g and then incident on the adjacent pixel is 100 pixels _ij r and 100 pixels.
_{Although i + 1 and jr} are different and the balance of the light amount is slightly unbalanced, compared to the case where the entire area of the image pickup device is configured with the pixel shown in FIG. 1, light is efficiently received even in the peripheral portion. .

Next, let us consider the efficiency of taking in a light beam by using the transmission / reflection of the dichroic film. For example, in a CCD image sensor in which pixels with primary color filters that are said to have good color reproducibility are arranged in a mosaic pattern, R (red)
One G (green) and B (blue) optical filter is arranged between the microlens 2 and the photoelectric conversion region 3.

At this time, in the pixel provided with the red optical filter, only the red light is photoelectrically converted, and the blue light and the green light are absorbed by the optical filter to become heat. Similarly, in a pixel with a green optical filter, blue light and red light are not photoelectrically converted into heat, and in a pixel with a blue optical filter, green light and red light are not photoelectrically converted into heat. . That is, in each pixel of the conventional color image pickup device, only the light that has passed through the predetermined optical filter in the incident light flux is photoelectrically converted and output as an electric signal, so the light that cannot pass through the optical filter is converted into heat or the like. It has been abandoned.

FIG. 22 shows the spectral transmittance characteristics of the RGB color filters in the image sensor. Due to its high infrared transmittance, there is actually a further 650
Infrared cut filters that cut off wavelengths of nm and above are used in layers. As can be seen from this, only about 1/3 of visible light is effectively used in one pixel.

Considering the utilization efficiency for each color of RGB in more detail, for example, the RGB of the color image pickup device of the Bayer array is used.
The pixel area ratio is 1/4: 2/4: 1/4, where 1 is the area of one unit forming a regular array. Therefore, the green light utilization rate when the total light amount is 1. Is the product of the term of wavelength selectivity and the term of area ratio, 1/3 × 2/4 = 1 /
6. Red light and blue light are 1/3 × 1/4 = 1/12, which is 1/6 + 1/12 + 1/12 = 1/3 in total, which means that the utilization efficiency is 1/3. On the contrary, when the total amount of light is 1, green light is 2/3 × 2/4 = 1 /
3 is red light or blue light, and 2/3 × 1/4 = 1/6 is not effectively used.

Although the above description is based on the image pickup prevention using the primary color filter, about 1/3 of the visible light is not photoelectrically converted in the image pickup device using the predator filter and is effectively used. Not done. As described above, in both the primary color system and the complementary color system, the light utilization efficiency is low in the conventional single-plate type image pickup device because the image pickup surface is divided by the color filters.

FIG. 11 shows a simplified transmission characteristic of each color of the dichroic film. In FIG. 11, the inside of the transmission curve of each color is the reflection characteristic. Further, for simplification of calculation, it is assumed that all the light fluxes that do not pass are reflected and all the reflected light fluxes reach the adjacent pixels equally. Further, the pixel arrangement is shown in FIG.
It is assumed that the Bayer array such as

Considering the case where the light flux reflected by the dichroic film in the pixel receiving the green color is transmitted through the dichroic film in the blue pixel and taken into the blue photoelectric conversion section, as described above, the transmission characteristic of the green color is changed. Since the inside out has the reflection characteristic, the product of this curve and the blue transmission characteristic is obtained. FIG. 12 shows this. As for the remaining colors, the same goes for the remaining pixels, that is, those that reach from the green pixel to the red pixel are shown in FIG. 13, those that reach from the red pixel to the green pixel are FIG. 14, and those that reach from the blue pixel to the green pixel. What is done is shown in FIG.

Considering what is reflected from the adjacent pixel in the green pixel, since the pixel array is the Bayer array, the adjacent pixels are two red and two blue. Therefore, the luminous flux received by the green pixel from the adjacent pixel is {(blue reflection) × 1/4 × 2 + (red reflection) × 1/4 × 2}. Originally, the amount of light flux received by the green pixel is the integrated amount of the transmittance curve, so when this is set to 1, the value reflected from the red pixel is 0.74, and the amount reflected from the blue pixel is 0.85. Therefore, the total reflected light is 0.80, which is 1.80 times as large as the case where only the transmitted light flux is captured.

Considering a blue pixel, the number of adjacent green pixels is four. When the integral amount of the transmittance curve of the blue pixel is 1, the integral amount of FIG. 12 is 0.84. The luminous flux received from the adjacent pixel is {(green reflection) x 1
/ 4 × 4}, the total is 0.84, which is 1.84 times the original transmission amount.

Considering the last red pixel, the adjoining pixels are four green, which is the same as the blue pixel. If the integral amount of the transmittance curve of the red pixel is 1, the integral amount of FIG. 13 is 0.67. Since the luminous flux received from the adjacent pixels is {(green reflection) × 1/4 × 4}, the total is 0.
67, which is 1.67 times the original transmission amount.

As described above, if adjacent pixels such as the Bayer array are not of the same color, this structure is used to divide unnecessary wavelength components into adjacent pixels for all pixels.
By reflecting the light, photoelectric conversion can be performed as an effective wavelength component in an adjacent pixel, and light utilization efficiency can be significantly improved.

Further, as shown in FIG. 1, the shape of the dichroic film 4 which is the wavelength selecting section is not changed, and the apex 4P of the dichroic film which is the wavelength selecting section is higher than the chief ray M _L passing through the apex 2c of the microlens. The dichroic film 4, which is a wavelength selection unit, is arranged so as to be located on the center side of the image sensor 500. Therefore, the balance of the amount of light reflected by the dichroic film 4 which is the wavelength selection unit and re-incident on the photoelectric conversion unit of the adjacent pixel can be improved, and an appropriate optical low-pass effect can be obtained.

In this embodiment, when the pixels 100 are arranged, the angle formed by the first direction and the second direction is vertical, but the pixels 100 are arranged so as to have a honeycomb structure, that is, the first direction. The angle between the direction of and the second direction is 60
It may be in degrees or any other angle. It may also be one-dimensionally arranged.

Further, although the dichroic film 4 which is the wavelength selecting section is a quadrangular pyramid, it may be a polygonal pyramid such as a hexagonal pyramid or an octagonal pyramid.

(Second Embodiment) FIGS. 16 to 19 show a second embodiment of the present invention.

Elements having the same numbers as those in the first embodiment have the same functions. FIG. 16 is a cross-sectional view of the image sensor according to the present embodiment. FIG. 17 is an explanatory diagram of the wavelength selection unit 4 arranged in the image sensor. 18 and 1
FIG. 9 is a diagram showing the behavior of the light flux inside the image sensor in this structure.

The configuration shown in FIG. 16 is a pixel in the peripheral portion of the image pickup device (a pixel arranged in the vicinity of 41 kr in FIG. 17), and is located at a position away from the optical axis of the photographic lens (not shown). Therefore, the center of the pupil of the imaging lens is located on the right side, and the light flux incident on the microlens 2 has an angle from the right direction. Therefore, the microlens 2 is arranged on the right side of the center of the pixel.

Further, in the present embodiment, as shown in FIG. 16, the angles of the slopes of the dichroic film 4 which is the wavelength selection section are different (θ1 ≠ θ2). At this time, the bottom surface of the quadrangular pyramid forming the dichroic film 4 which is the wavelength selecting portion is formed in a shape in which only the apex 4P of the quadrangular pyramid is offset to the right side while being aligned with the boundary 15 of the pixel.

Contrary to FIG. 16, when the center of the pupil of the imaging lens is located on the left side, the dichroic film 4 as the wavelength selecting section is arranged so that the vertex 4P is located on the left side. At this time as well, similarly to the above, θ1 ≠ θ2.

FIG. 17 is an explanatory diagram of the wavelength selecting section 4 arranged in the image pickup device. What is shown in the periphery of the image pickup device in this figure is an enlarged view of the wavelength selection unit 4 at each position.

In the peripheral part of the image pickup device, the apex 4P of the dichroic film which is the wavelength selection part is located closer to the center of the image pickup device than the central axis 3c which is determined by the photoelectric conversion part. Is changing the shape of. That is, in the wavelength selection unit 4, θ1 ≠ θ2, and further, the position of the bottom surface of the dichroic film 4 and the position of the pixel match.

Next, the behavior of a light beam having a predetermined angle of view that is incident on the image sensor of this embodiment will be described.

FIG. 18 shows the behavior of the light beam which is transmitted through the dichroic film 4 which is the wavelength selection section. The light flux coming from the upper part of the figure enters the microlens 2 and is subjected to a condensing function. Next, the first refractive index layer 5 and the second refractive index layer 6 are sequentially incident to reach the dichroic film 4g. In the dichroic film 4 which is the wavelength selection unit, only the light flux having a predetermined wavelength is selectively transmitted and is incident on the first refractive index unit 7. Then, the light travels to the second refractive index section 8 and is guided to the photoelectric conversion section 3 by being subjected to the action of repeating total reflection at the interface between the second refractive index section 8 and the third refractive index section 9. Second
Since the interface between the refraction part 8 and the third refraction part 9 has a tapered shape in which the incident part is widened, it can be totally reflected and guided to the photoelectric conversion part 3 even on the tapered surface.

FIG. 19 shows a pixel 100 _ij which receives green light.
The behavior of only the light flux that is incident on g and reflected by the dichroic film 4g, that is, only the light flux including blue light and red light is shown. A light beam emitted from the pupil of the imaging lens at a position far away from the size of the pixel passes through the infrared cut filter and becomes a light beam like the object light 120. The object light 120 coming from the upper part of the figure is incident on the microlens 2 and is condensed. Next, the first refractive index layer 5 and the second refractive index layer 6 are sequentially incident to reach the dichroic film 4g. Here, due to the characteristics of the dichroic film 4g, light beams other than green are reflected. Since the dichroic film 4g is formed on the surface having the shape of a quadrangular pyramid, the reflected light beam travels while changing its direction from the center to the outside.

The light reflected by the dichroic film 4g is totally reflected at the interface between the second refractive index layer 6 and the first refractive index layer 5 by a light beam having a critical angle or more. The light flux directed downward again is the pixel 10 that receives the red light which is the adjacent pixel.
Proceed towards ₀ ijr and 100 _{i + 1 , j} r. The light flux that has passed through the dichroic film 4r proceeds in order to the first refractive index portion 7 and the second refractive index portion 8. Then the second
From the refractive index portion 8 of the second refractive index portion 8 to the third refractive index portion 9, but since the second refractive index portion 8 has a higher refractive index than the third refractive index portion 9 as described above, A light beam having a critical angle or more is totally reflected at the interface. Since the interface between the second refractive index portion 8 and the third refractive index portion 9 has a tapered shape in which the incident portion is widened, the frontage for capturing the incident light flux is wide, and a large amount of the luminous flux is captured in the second refraction portion 8. Is able to.
Since the interface in the vicinity of the photoelectric conversion unit 3 is formed by two surfaces that are substantially parallel to the vertical direction, the light flux that has not entered the photoelectric conversion unit 3 due to the first total reflection is totally reflected again at the interface on the opposite side. Eventually, all will enter the photoelectric conversion unit 3.

In the structure of the present embodiment, the dichroic film which is the wavelength selection unit is arranged so that the vertex 4P of the dichroic film which is the wavelength selection unit is located closer to the center of the image sensor than the central axis 3c determined by the photoelectric conversion unit. The shape of the film is changing. That is, the wavelength selection unit 4 is configured such that θ1 ≠ θ2, and further, the position of the bottom surface of the dichroic film 4 and the position of the pixel match.

Therefore, the angles of the light fluxes incident on the right slope and the left slope can be matched, whereby the light fluxes reflected on the right and left slopes of the wavelength selecting section 4 have the first and second refractive indices. The light enters the layer interface 5i at an appropriate angle.

As a result, it is possible to take in a light flux having a wider field angle than that of an image pickup lens (not shown) in the pixels around the image pickup element.

In the present embodiment, the angle formed by the first direction and the second direction when the pixels 100 are arranged is vertical, but the pixels 100 are arranged so as to have a honeycomb structure, that is, the first direction. The angle between the direction of and the second direction is 60
It may be in degrees or any other angle. It may also be one-dimensionally arranged.

Further, although the dichroic film 4 which is the wavelength selecting portion is a quadrangular pyramid, it may be a polygonal pyramid such as a hexagonal pyramid or an octagonal pyramid.

(Third Embodiment) Based on FIG. 20,
An image pickup apparatus using the image pickup element having the configuration described in the above-described first embodiment and second embodiment will be described.

In FIG. 20, reference numeral 201 denotes a barrier which also serves as a lens protector and a main switch, 202 denotes a lens for forming an optical image of a subject on an image pickup element 204, and 203.
Is an aperture for changing the amount of light passing through the lens 202, 2
Reference numeral 04 denotes an image sensor for capturing the subject formed by the lens 202 as an image signal, and 205 denotes an image sensor 204.
An image pickup signal processing circuit including a variable gain amplifier section for amplifying an image signal output from the image pickup apparatus, a gain correction circuit section for correcting a gain value, and the like. Reference numeral 206 denotes an analog-digital conversion of an image signal output from the image pickup element 204. Do A /
A D converter, 207 is a signal processing unit that performs various corrections on image data output from the A / D converter 206, and compresses the data, and 208 is an image sensor 204, an image signal processing circuit 205, and an A / D converter. 206, a timing generation unit for outputting various timing signals to the signal processing unit 207, 209
Is an overall control / arithmetic unit for controlling various calculations and the entire imaging apparatus, 210 is a memory unit for temporarily storing image data, 211 is an interface unit for recording or reading on a recording medium, and 212 is image data. A removable recording medium 213 such as a semiconductor memory for recording or reading the data is an interface unit for communicating with an external computer or the like.

Next, the operation of the image pickup apparatus having the above-described structure during photographing will be described.

When the barrier 201 is opened, the main power source is turned on, then the control system power source is turned on, and further the image pickup system circuit such as the A / D converter 206 is turned on.

Then, in order to control the exposure amount, the overall control / arithmetic unit 209 opens the diaphragm 203, and the image pickup device 2
The signal output from 04 is converted by the A / D converter 206 and then input to the signal processing unit 207.

Overall control of exposure calculation based on the data
The calculation unit 209 performs this. The brightness is determined based on the result of the photometry, and the overall control / calculation unit 209 is determined according to the result.
Controls the aperture.

Next, based on the signal output from the image pickup device 204, a high frequency component is extracted and the calculation of the distance to the subject is performed by the overall control / calculation unit 209. After that, the lens is driven to determine whether or not it is in focus. When it is determined that the lens is not in focus, the lens is driven again to measure the distance.

Then, after the focus is confirmed, the main exposure starts.

When the exposure is completed, the image signal output from the image pickup device 204 is A / D converted by the A / D converter 206, passes through the signal processing unit 207, and is written in the memory unit by the overall control / arithmetic unit 209. Then, the memory unit 220
The data accumulated in (1) is recorded on the removable recording medium 212 such as a semiconductor memory through the recording medium control I / F section under the control of the overall control / arithmetic unit 209.

Further, the image may be processed by directly inputting it to a computer or the like through the external I / F section 213.

[0082]

According to the present invention, it is possible to obtain an appropriate optical low-pass effect even in the peripheral portion of the image pickup device and improve the light utilization efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a first exemplary embodiment of the present invention.

FIG. 3 is a top view of the image sensor according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a wavelength selection unit arranged in the image sensor according to the first embodiment of the present invention.

FIG. 5 is a ray trace diagram (transmitted light) of the first embodiment of the present invention.

FIG. 6 is a ray trace diagram (reflected light) according to the first embodiment of the present invention.

FIG. 7 is a ray trace diagram (reflected light) according to the first embodiment of this invention.

FIG. 8 is a diagram showing a pixel configuration.

FIG. 9 is a diagram showing a configuration of a dichroic film.

FIG. 10 is a diagram showing characteristics of a dichroic film.

FIG. 11 is a simplified diagram showing characteristics of a dichroic film.

FIG. 12 is a simplified diagram showing characteristics when reflected by a G transmission dichroic film and transmitted by a B transmission dichroic film.

FIG. 13 is a simplified diagram showing characteristics when reflected by a G transmission dichroic film and transmitted by an R transmission dichroic film.

FIG. 14 is a simplified diagram showing characteristics when reflected by an R transmission dichroic film and transmitted by a G transmission dichroic film.

FIG. 15 is a simplified diagram showing characteristics when reflected by a B transmission dichroic film and transmitted by a G transmission dichroic film.

FIG. 16 is a diagram showing a second example of the present invention.

FIG. 17 is an explanatory diagram of a wavelength selection unit arranged in the image sensor according to the second embodiment of the present invention.

FIG. 18 is a ray trace diagram (transmitted light) of the second embodiment of the present invention.

FIG. 19 is a ray trace diagram (reflected light) according to the second embodiment of the present invention.

FIG. 20 is a diagram showing a third exemplary embodiment of the present invention.

FIG. 21 is a diagram showing a conventional form.

FIG. 22 is a diagram showing characteristics of a conventional color filter.

[Explanation of symbols]

1 Silicon Wafer 2 Microlens 2c Microlens Vertex 3 Photoelectric Converter 3c Central Axis Determined by Photoelectric Converter 4 Wavelength Selector 4g, 411g, 41kg, 4mkg, 4mng Green Transmitting Wavelength Selector 4r, 41kr, 4knr, 4kkr Red Transmission wavelength selecting section 4m1b Blue transmission wavelength selecting section 4P Wavelength selecting section apex 5 First refractive index layer 6 Second refractive index layer 7 First refractive index section 8 Second refractive index section 9 Third Refractive index portion 10 Poly wiring layer 11 AL1 wiring layer 12 AL2 wiring layer 13 AL3 wiring layer 15 Pixel boundary 41 Color filter 61 Imaging device (conventional) 61 mnr Red pixel 61 mng, 61 mng2 Green pixel 61 mnb Blue pixel 100 pixel 100 _ij g green pixel _{100 ij r, 100 i + 1} , j r red pixel 200g green pixel 12 Object beam 901 effective pixel aperture

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akihiko Nagano             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation F term (reference) 2H048 FA01 FA05 FA15 FA24 GA01                       GA04 GA13 GA24 GA33                 4M118 AB01 CA31 GC07 GD02 GD04                       GD07 GD10                 5C024 AX01 CX00 EX42 EX43 EX52                       GY01

Claims (8)

[Claims] 1. An image pickup device in which a plurality of pixels including a photoelectric conversion unit and a wavelength selection unit that transmits light in a predetermined wavelength range to the photoelectric conversion unit are arranged, wherein the wavelength selection unit has an apex. In the pixel which is a structure and is located in a peripheral portion of the image pickup device, an apex of the wavelength selection unit is located in a central direction of the image pickup device rather than a center of the photoelectric conversion unit. element. 2. The wavelength selecting unit according to claim 1,
An imaging device characterized by being a polygonal pyramid. 3. The image pickup device according to claim 1, wherein the wavelength selection units included in each of the plurality of pixels have the same shape. 4. The shape of the wavelength selection unit included in the pixel arranged at the first position of the image sensor and the pixel arranged at the second position of the image sensor according to claim 1 or 2. An image pickup device having a shape different from that of the wavelength selection unit included therein. 5. The wavelength selection unit according to claim 1, wherein each of the plurality of pixels has a microlens that collects light, and the pixels located in a peripheral portion of the image sensor are the wavelength selection unit. Is the center of the microlens,
An image pickup device, which is located closer to the center of the image pickup device than an optical axis connecting the center of the photoelectric conversion unit. 6. The first refractive index region according to claim 1, wherein the first refractive index region has a predetermined refractive index on a light incident side with respect to the wavelength selection unit, and the first refractive index region includes the first refractive index region. Also has a second refractive index region having a predetermined refractive index provided on the light incident side, and the refractive index of the first refractive index region is higher than the refractive index of the second refractive index region. An image pickup device characterized by. 7. The high refractive index region according to claim 1, having a predetermined refractive index that guides light to the photoelectric conversion unit provided between the wavelength selection unit and the photoelectric conversion unit. And a low-refractive-index region having a lower refractive index than the high-refractive-index region provided around the high-refractive-index region. 8. An image pickup device according to claim 1, an analog / digital conversion circuit for converting a signal from the image pickup device into a digital signal, and a signal of the analog / digital conversion circuit. An image pickup apparatus comprising: a signal processing circuit for processing.