JP2003243639A - Image pickup element and image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a light converging rate to a photoelectric conversion part. <P>SOLUTION: This image pickup element is provided with a photoelectric conversion part, a wavelength selecting part which is formed on a light incidence side to the photoelectric conversion part and transmits a light in a prescribed wavelength range, a first region which is formed on a light incidence side to the wavelength selecting part and has a prescribed refractive index, and a second region which is formed on a light incidence side to the first region and has a prescribed refractive index. The refractive index of the first region is higher than that of the second region. <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 FIG. 35 shows the structure of a general image pickup device for forming a color image. FIG. 35 is a central cross-sectional view of pixels that form the image sensor 61. Reference numeral 101 denotes a microlens that collects light rays from the outside and plays a role of increasing the light-trapping efficiency. Reference numeral 102 denotes a color filter used for wavelength-separating the captured light rays. A primary color filter of either (green) or 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 61 used here often has a configuration called a Bayer array. 61 mn
g is the first green pixel, 61 mnb is the blue pixel, 61
mnr is a red pixel and 61mng2 is a second green pixel. m represents the array number of pixels in the horizontal direction, and n represents the array number of pixels in the vertical direction. One image pickup device is configured by regularly arranging these as shown in FIG. In such a pixel arrangement, green pixels have twice as many pixels as blue and red pixels. Basically, it is possible to create a color image with the same number of three colors, but the image quality can be improved by increasing the number of green pixels having relatively high visibility.

[0003]

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 Func
Tion) is an evaluation amount that can well express the characteristics relating to the sharpness of a digital still camera or a video camera. 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 image characteristics of is given as the product of the MTFs 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, that is, 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 in which the spatial frequency characteristic of the optical image has a component having a frequency equal to or higher than the Nyquist frequency peculiar to the image pickup device 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 imaging 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 gaps, 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. If the thickness of the birefringent plate is appropriately selected, it is possible to make the response zero at the Nyquist frequency of the image sensor. 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 a crystal such as quartz or lithium niobate and then thinly polish it, which is extremely 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. 37 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 of the RGB colors in more detail, for example, the RGB pixel area ratio of the color image pickup device of the Bayer array shown in FIG. 102 is 1 when the area of one unit forming the regular array is 1. / 4: 2/4: 1/4
Therefore, when the total amount of light is 1, the utilization ratio of green light is 1/3 × as the product of the term of wavelength selectivity and the term of area ratio.
2/4 = 1/6, 1/3 × 1/4 = 1 for red light and blue light
/ 12, totaling 1/6 + 1/12 + 1/12 = 1 /
With 3, the utilization efficiency is 1/3. vice versa,
When the total amount of light is 1, green light is 2/3 x
2/4 = 1/3 is 2/3 × 1/4 = for red light and blue light
1/6 will not be used effectively.

Although the image pickup device using the primary color filter has been described above, in the image pickup device using the complementary color filter, about 1/3 of visible light is not photoelectrically converted 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 such conventional problems, and one object of the present invention is to realize an image pickup device with improved utilization efficiency of incident light.

[0019]

In order to solve the above problems, a photoelectric conversion unit and a wavelength selection unit formed on the light incident side of the photoelectric conversion unit and transmitting light in a predetermined wavelength range, A first region having a predetermined refractive index formed on the light incident side of the wavelength selection unit, and a first region having a predetermined refractive index formed on the light incident side of the first region. And a second region, wherein the refractive index of the first region is higher than the refractive index of the second region.

[0020]

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 cross-sectional view of an image sensor, 1 is a silicon wafer, 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 separation of light rays, and 6 is a first refractive index 1 is a refractive index region, 5 is a second refractive index region having a second refractive index, 8 is a third refractive index region having a third refractive index, and 9 is a fourth refractive index region having a fourth refractive index. Refractive index region, 7 is a fifth refractive index region having a fifth refractive index, 10
Is a gate that controls the charge of the photoelectric conversion part P
It is an olly wiring layer. 11 to 13 are wiring layers made of a metal such as aluminum, 11 is an AL1 wiring layer which plays a role of connection and output line between respective parts, 12 is an AL2 wiring layer which plays a role of well power supply line and control line, and 13 is This is an Al3 wiring layer that functions as a light shield and a power supply line. Also,
FIG. 2 is a perspective view of the image pickup device as seen from an obliquely upper surface, and only nine of the many image pickup devices are extracted and illustrated. Further, FIG. 3 shows the microlens 2 at the center of FIG.
2A and 2B are cross-sectional views in which the structure from the dichroic film 4 to the AL3 wiring layer is cut.

In FIG. 1, the microlens 2 has a spherical surface convex upward and has a positive lens power. Therefore, the light beam reaching the microlens 2 has a function of condensing on the photoelectric conversion unit 3. As a result, more light rays can be taken into the photoelectric conversion unit 3, so that the sensitivity of the image sensor can be increased. The second refractive index region 5 in contact with the microlens 2 plays a very important optical role in this structure in combination with the first refractive index region 6. The second refractive index region 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. Also, the second
The first refractive index region 5 sandwiched between the refractive index region 5 and the dichroic film 4 is made of a high refractive index material, and for example, titanium dioxide (TiO ₂ ) having a refractive index of 2.5 may be used. it can. First by adopting such a configuration
A light ray traveling from the refractive index area 6 to the second refractive index area 5 has the property of being easily totally reflected at the interface.

Third refractive index region 8 and fourth refractive index region 9
And the fifth index region 7 forms the second important optical element in the structure. The first refractive index region 8 is formed of a high refractive index material such as titanium dioxide, and the fourth refractive index region 9 is formed of silicon dioxide (Si having a refractive index of 1.46).
It is molded using a material having a low refractive index such as O ₂ ) or magnesium fluoride. As a result, the light ray incident on the third refractive index region is likely to be totally reflected at the interface with the fourth refractive index region, and thus serves as a light guide path to reach the photoelectric conversion unit 3. Since the fifth refractive index region 7 needs not to be totally reflected at the interface with the third refractive index region, it is formed of a material having a refractive index equal to or lower than that of the third refractive index region. There is a need. However, since it is preferable that the difference in the refractive index from the first refractive index region 6 is not so large, for example, silicon nitride (Si ₃ N ₄ ) having a refractive index of 2.0 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 can be selected. FIG. 18 shows an example of the dichroic film 4 used in this embodiment.
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 the figure. The transmission characteristics of this dichroic film 4 are shown in FIG. As can be seen from the characteristic diagram of FIG. 19, it has a characteristic close to that of the characteristic diagram of the color filter using the conventional dye shown in FIG. 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 are PVD (Phys
It can be easily prepared by using the ICP.

Next, the behavior of light rays in the image pickup device in this structure will be described with reference to FIGS. FIG. 6 shows the behavior of only light rays that are incident on the pixel 100g that receives green light and are reflected by the dichroic film 4g, that is, light rays that include blue light and red light. 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 110. The object light 110 coming from the upper part of the figure is incident on the microlens 2 and is subjected to a condensing function. Next, the second refractive index region 5 and the first refractive index region 6 are sequentially incident to reach the dichroic film 4g. Light rays other than green are reflected by the characteristics of the dichroic film 4g.
As a result, the light travels in the direction of the second refractive index region 5, but since the dichroic film 4g is formed on the surface having the shape of a quadrangular pyramid as shown in FIG. Change direction to the outside and proceed. As described above, since the first refractive index region 6 has a higher refractive index than the second refractive index region 5, a light ray having a critical angle or more is totally reflected at the interface. The light rays totally reflected at the interface are directed toward the dichroic film 4r and travel toward the adjacent pixels, that is, pixels 100r and 101r that receive red light.
Dichroic film 4 of these pixels 100r, 101r
r has a characteristic of transmitting red light and reflecting green light and blue light. Therefore, of the light rays reflected from the pixel 100g, only the red light is transmitted and the blue light is reflected by the dichroic film 4r. Here, the blue light, which is subjected to the reflection action, travels outside the image sensor and is not shown. The dichroic film 4r, through which the reflected light is transmitted, has a small area that can be transmitted by the thickness of the film. It is smaller than the opening area. Therefore, the reflected light rays can be transmitted through the dichroic film 4r without vignetting.
The light ray that has passed through the dichroic film 4r proceeds in order to the fifth refractive index area 7 and the third refractive index area 8. The interface between the third refractive index region 8 and the fourth refractive index portion 9 has a tapered shape in which the incident portion is widened, so that the incident light ray is less likely to be vignetted. Subsequently, the third refractive index region 8 tries to proceed to the fourth refractive index region 9, but as described above, the third refractive index region 8 has a higher refractive index than the fourth refractive index region 9. Therefore, a light ray having a critical angle or more is totally reflected at the interface. Further, since this interface is formed by two surfaces that are substantially parallel to the vertical direction, the light rays that have not entered the photoelectric conversion unit 3 due to the first total reflection are totally reflected again at the opposite interface, and finally All will be incident on the photoelectric conversion unit 3.

In the pixel 100g, there is a pixel that receives blue light in a direction perpendicular to the paper surface. Similar to the case of red, this also exhibits a behavior of capturing only blue light among the light rays reflected by the pixel 100g.

FIG. 7 shows the behavior of light rays which are transmitted through the dichroic film 4. Light rays coming from the upper part of the figure enter the microlens 2 and are subjected to a condensing function.
Next, the second refractive index region 5 and the first refractive index region 6 are sequentially incident to reach the dichroic film 4g. The dichroic film 4g selectively transmits only a light beam having a predetermined wavelength and makes it enter the fifth refractive index region 7. When traveling to the third refractive index region 8, the light beam is bent toward the center because the refractive index of the third refractive index region is higher and the prism shape is obtained. This action makes it possible to capture a wider range of light rays. Further, since the interface between the third refractive index region 8 and the fourth refractive index region 9 has a tapered shape in which the incident portion is widened, it is possible to capture a wide range of light rays. Furthermore, the third refractive index region 8 and the fourth refractive index region 9
It is assumed that the photoelectric conversion portion 3 is guided by being subjected to the effect of repeating total reflection at the interface of. From this, it can be seen that a sufficiently wide range of light rays can be taken in with respect to transmitted light.

Next, let us consider the efficiency of capturing a light beam by using the transmission / reflection of the dichroic film. Figure 20
Is a simplification of the transmission characteristics of each color of the dichroic film. The inside of the transmission curve of each color is the reflection characteristic. Further, for simplification of calculation, it is assumed that all light rays that do not pass are reflected and that all reflected light rays reach the adjacent pixels equally. Further, the pixel array is assumed to be a Bayer array as shown in FIG.

Considering the case where the light rays reflected by the dichroic film in the green pixel are transmitted through the dichroic film in the blue pixel and taken into the blue photoelectric conversion section, as described above, the inside-out of the transmission characteristic of green is reversed. Because it has reflective characteristics,
The product of this curve and the blue transmission characteristic is obtained.
FIG. 21 shows this. As for the rest of the colors, the same goes for the green pixels to reach the red pixels in FIG. 22, the red pixels to reach the green pixels in FIG. 23, and the blue pixels to reach the green pixels. 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 pixel has two red pixels and two blue pixels. From this, the light ray that the green pixel receives from the adjacent pixel is {(blue reflection) x 1/4 x 2 + (red reflection) x 1/4 x 2}.
Becomes Since the amount of light rays originally received by a green pixel is the integrated amount of the transmittance curve, the size of FIG. 23 (reflected from a red pixel) is 0.37, and the size of FIG. (Reflected one) is 0.43.
Therefore, the total reflected light is 0.39, which is 1.39 times as large as the case where only the transmitted light beam is taken in.

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. 21 is 0.84. Rays received from adjacent pixels are {(green reflection) x 1/4 x
4}, the total is 0.84, which is 1.84 times the original transmission amount.

Considering the last red pixel, the adjacent pixels are four green, which is the same as the blue pixel. When the integral amount of the transmittance curve of the red pixel is 1, the integral amount of FIG. 22 is 0.67. It can be seen that since the light rays received from the adjacent pixels are {(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 do not have the same color, unnecessary wavelength components of all the pixels are divided and reflected by the adjacent pixels, so that the effective wavelengths of the adjacent pixels can be obtained. Photoelectric conversion can be performed as a component, and light utilization efficiency can be significantly improved.

Next, the low-pass filter effect as the second operation of this configuration will be described. In the image sensor according to the embodiment of the present invention, the substantial light receiving aperture is larger than each pixel. Compared with the conventional image sensor of the Bayer array shown in FIG. 8 for each color of RGB, first, the aperture of the conventional G pixel was the size of the microlens. However, in the image sensor according to the present embodiment of the present invention, 92a, 9 as shown in FIG.
Since the portions 2b, 92c, and 92d are received from the adjacent pixels, they are larger than the original pixel opening 91. As a result, a substantial light receiving aperture including that of receiving the green light component from the adjacent pixel is as shown in FIG. B
Also for pixels and R pixels, since the respective color light components are separated from the adjacent pixels, the effective light receiving opening has the same shape.
Therefore, considering all the pixels, it can be seen that the pixels have light receiving apertures that effectively overlap each other.

When the substantial light receiving aperture is larger than each pixel in this way, it is possible to obtain an MTF characteristic which has not been considered in a normal single plate type image pickup device. As a result, the quality of the image is not deteriorated even if the optical low-pass filter is omitted. That is, a high-quality image in which aliasing distortion is not conspicuous can be obtained only by omitting the second process for adjusting the high frequency component of the spatial frequency characteristic of the object image and performing the photoelectric conversion of the object image. It is possible.

11 to 17 are explanatory views thereof.

First, FIG. 11 shows the MTF characteristic with respect to the spatial frequency component in the horizontal direction of the pixel 110g of the image sensor according to the embodiment of the present invention. Further, FIG. 12 shows MTF characteristics of a pixel having a normal type rectangular opening. In each case, the size of one pixel was □ 3 μm, and the microlens had a size of one pixel. Furthermore, the pixel according to the present embodiment of the present invention has an opening extending to the center of the adjacent pixel.

The response of the conventional rectangular aperture pixel shown in FIG. 8 can be simply expressed by the SINC function as shown in equation (2).

[0038]

[Outer 1]

Here, R3 (u) is the response, and d is
It is the width of the light receiving aperture of the image sensor.

The first zero point (cutoff frequency) of the equation (2) is the position of u = 1 / d. That is, the response becomes zero at the wavelength corresponding to the width of the light receiving aperture.
In an image sensor in which the light receiving apertures are spread without gaps, the width of the light receiving apertures matches the pixel pitch, so the response value of the equation (2) at Nyquist frequency u = d / 2 is 0.636, which is considerably high. Therefore, it is necessary to use the optical low-pass filter having the MTF characteristic shown in FIG. 13 together with the conventional rectangular aperture pixel. here,
When assuming still images to be viewed, such as with a digital still camera, there is a high sense of resolution when the high frequencies above the Nyquist frequency are not zero, but the response at a frequency slightly below the Nyquist frequency is high Considering that it tends to be an image.

On the other hand, the pixel 1 according to the present embodiment
At 00g, the response extends to the high frequency side due to the diamond-shaped opening as shown in FIG. This is formula (2)
It can be considered that an infinitely narrow strip-shaped rectangular opening that can express the MTF characteristic is collected. The result obtained by integrating the entire rectangular opening is as shown in FIG. 11. It can be seen that the pixel 100 g has a considerably lower response at the Nyquist frequency of 167 lines / mm when the pixel pitch is 3 μm. I understand. Next, FIG. 14 shows the MTF characteristics of the aberration-free lens when the F number is 4.0 and the wavelength of the object image is 550 nm. In an ideal lens having no geometrical aberration, its MTF is determined by the diffraction of light. The diffraction limit MTF is determined by the F number and is represented by the equation (3).

[0042]

[Outside 2]

Β = cos ⁻¹ (u · F · λ) where u is the spatial frequency of the optical image and F is the F of the optical system.
The number, λ, is the wavelength of the optical image.

The cutoff frequency of this imaging lens is 45
5 / mm.

Now, the first process for forming the object image by the optical device, (the second process for adjusting so as to suppress the high frequency component of the spatial frequency characteristic of the object image).
Photoelectric conversion of an object image with adjusted spatial frequency characteristics Third
The materials to know the total MTF of the process have been prepared.

FIG. 15 shows a total MTF of the image forming lens and the pixel of the image pickup element when the pixel 100g is used. On the other hand, FIG. 16 shows a total MTF of the pixels of the imaging lens, the optical low-pass filter, and the image sensor when the conventional pixels are used. Both have substantially the same response at the Nyquist frequency of 167 lines / mm, and have similar characteristics as a whole. On the other hand, if the conventional pixel does not use the optical low-pass filter, the response at the Nyquist frequency becomes too high as shown in FIG. Thus, it can be seen that the optical low-pass filter can be omitted by using the pixel 100g.

(Second Embodiment) FIG. 25 shows a second embodiment. Those having the same number shall perform the same function. The behavior of light rays in the image sensor in this structure is as shown in FIGS. Similar to the first embodiment, FIG. 26 shows the behavior of only the light rays that are incident on the pixel 200g that receives the green light and reflected by the dichroic film 4g, that is, the light rays that include the blue light and the red light. The 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 second refractive index area 5 and the first refractive index area 6
Sequentially enters and reaches the dichroic film 4g. Light rays other than green are reflected by the characteristics of the dichroic film 4g. Since the dichroic film 4g is formed on the surface having the shape of a quadrangular pyramid as shown in FIG. 4, the reflected light ray changes its direction from the center to the outside and travels. Then, at the interface between the first refractive index region 6 and the second refractive index region 5, a light ray having a critical angle or more is totally reflected. The light rays directed downward again travel toward the adjacent pixels 200r and 201r that receive red light. The light ray that has passed through the dichroic film 4r proceeds in order to the fifth refractive index area 7 and the third refractive index area 8. When traveling to the third refractive index region 8, since the shape thereof is a quadrangular pyramid in the first embodiment, the light beam is incident on the surface at an angle close to a right angle. In this configuration, since the third refractive index region 8 has a flat surface, the incident angle becomes small, and there is an action of being largely bent toward the center. Therefore, more rays than in the first embodiment can be totally reflected at the interface between the third refractive index region 8 and the fourth refractive index region 9. The light reaches the photoelectric conversion unit 3 by repeating total reflection at the interfaces of these regions.

FIG. 27 shows the behavior of light rays which are transmitted through the dichroic film 4. Light rays coming from the upper part of the figure enter the microlens 2 and are subjected to a condensing function. Next, the second refractive index region 5 and the first refractive index region 6 are sequentially incident to reach the dichroic film 4g. The dichroic film 4 selectively transmits only light rays having a predetermined wavelength and makes them incident on the fifth refractive index portion 7. Further, the effect of repeating total reflection at the interface between the third refractive index region 8 and the fourth refractive index region 9 leads to the photoelectric conversion unit 3. As a result, it is possible to capture a sufficiently wide range of transmitted light.

(Third Embodiment) FIG. 28 shows a third embodiment. Those having the same number shall perform the same function. The behavior of light rays in the image sensor in this structure is as shown in FIGS. Similar to the first embodiment, FIG. 29 shows the behavior of only the light rays that are incident on the pixel 100g that receives the green light and reflected by the dichroic film 4g, that is, the light rays that include the blue light and the red light. A light ray 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 130. The object light 130 coming from the upper part of the figure enters the microlens 2 and is subjected to a condensing function. Next, the second refractive index area 5 and the first refractive index area 6
Sequentially enters and reaches the dichroic film 4g. Light rays other than green are reflected by the characteristics of the dichroic film 4g. Since the dichroic film 4g is formed on the surface having the shape of a quadrangular pyramid as shown in FIG. 4, the reflected light ray changes its direction from the center to the outside and travels. Then, at the interface between the first refractive index region 6 and the second refractive index region 5, a light ray having a critical angle or more is totally reflected. At that time, since the interface between the second refractive index region 5 and the first refractive index region 6 has a spherical shape that is convex upward, the interface plays a role of a concave mirror and functions to collect light. As a result, the light fluxes can be collected after reflection, so that a wide range of light rays can be captured. The behavior of the light beam until reaching the photoelectric conversion unit 3 thereafter is the same as that of the second embodiment.

FIG. 30 shows the behavior of light rays which are transmitted through the dichroic film 4g. The behavior of the light beam coming from the upper part of the figure to reach the photoelectric conversion unit 3 is the second
This is the same as the embodiment. As is clear from this figure,
As for transmitted light, it is possible to capture a sufficiently wide range of light rays.

(Fourth Embodiment) FIG. 31 shows a fourth embodiment. Those having the same number shall perform the same function. In the present embodiment, the microlens 2 needs to be easily totally reflected at the interface with the first refractive index region 6, so it is preferable to use a material having a low refractive index such as magnesium fluoride or silicon dioxide. The behavior of light rays in the image sensor in this structure is as shown in FIGS. Similar to the first embodiment, FIG. 31 shows that the dichroic film 4 is made incident upon the pixel 100g that receives green light.
The behavior of only the light rays reflected by g, that is, the light rays including blue light and red light is shown. A light ray 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 140. The object light 140 coming from the upper part of the figure enters the microlens 2 and is subjected to a condensing function. Next, it reaches the dichroic film 4g through the first refractive index region 6. The behavior of the light beam until reaching the photoelectric conversion unit 3 thereafter is the same as that of the second embodiment.

FIG. 33 shows the behavior of light rays which are transmitted through the dichroic film 4. Light rays coming from the upper part of the figure enter the microlens 2 and are subjected to a condensing function. Next, through the first refractive index region 6, the dichroic film 4
reach g. After that, the behavior until reaching the photoelectric conversion unit 3 is similar to that of the second embodiment. As is clear from this figure, it is possible to capture a sufficiently wide range of transmitted light. By adopting the structure of this embodiment, the layer structure for forming the total reflection surface can be reduced by one layer.

The solid-state image pickup device having the configuration of the first to fourth embodiments described above may be a charge transfer type such as a CCD type solid-state image pickup device or a CMOS image sensor.
It may be an XY address type such as a di-sensor.

(Fifth Embodiment) Based on FIG. 34,
An image pickup apparatus using the solid-state image pickup element having the configuration described in the first to fourth embodiments described above will be described.

In FIG. 34, 101 is a barrier which also serves as a lens protector and a main switch, 102 is a lens for forming an optical image of a subject on a solid-state image sensor 104, and 1 is a lens.
Reference numeral 03 denotes a diaphragm for varying the amount of light passing through the lens 102, 104 denotes a solid-state image sensor for taking in a subject imaged by the lens 102 as an image signal, and 105 denotes an image signal output from the solid-state image sensor 104. An image pickup signal processing circuit including a variable gain amplifier unit for amplifying and a gain correction circuit unit for correcting a gain value, and 106 is an A / D converter for performing analog-digital conversion of an image signal output from the solid-state image pickup device 104. , 107 are A / D converters 1
The signal processing unit 108 performs various corrections and compresses the image data output from the solid-state image sensor 1
04, imaging signal processing circuit 105, A / D converter 106,
A timing generation unit that outputs various timing signals to the signal processing unit 107, 109 is an overall control / arithmetic unit that controls various calculations and the entire imaging apparatus, 110 is a memory unit for temporarily storing image data, and 111 is An interface unit for recording or reading on a recording medium, 112 is a removable recording medium such as a semiconductor memory for recording or reading image data, and 113 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 1 is opened, the main power source is turned on, then the control system power source is turned on, and
The power supply of the imaging system circuit such as the / D converter 106 is turned on.

Then, in order to control the exposure amount, the overall control / arithmetic unit 109 opens the diaphragm 103, the signal output from the solid-state image sensor 104 is converted by the A / D converter 106, and then signal processed. It is input to the unit 107.

Overall control of exposure calculation based on the data
The calculation unit 109 performs this. The brightness is determined based on the result of this photometry, and the overall control / calculation unit 109 is determined according to the result.
Controls the aperture.

Next, based on the signal output from the solid-state image pickup device 104, a high frequency component is extracted and the distance to the object is calculated by the overall control / calculation unit 109. 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 solid-state image pickup device 104 is A / D converted by the A / D converter 106, passes through the signal processing unit 107, and the overall control / calculation unit 10 is operated.
9 is written in the memory section. After that, the memory unit 1
The data accumulated in 10 passes through the recording medium control I / F unit under the control of the overall control / arithmetic unit 109 and is recorded in the removable recording medium 12 such as a semiconductor memory.

Further, the image may be processed by directly inputting it to a computer or the like through the external I / F unit 113.

[0064]

According to the present invention, light can be efficiently condensed by the photoelectric conversion section.

[Brief description of drawings]

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

FIG. 2 is a perspective view of the first embodiment of the present invention.

FIG. 3 is a sectional perspective view of the first embodiment of the present invention.

FIG. 4 is a perspective view showing a dichroic film portion.

FIG. 5 is a perspective view showing a structure of a second refractive index portion.

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 (transmitted 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 situation where a green pixel captures light rays.

FIG. 10 is a diagram showing an effective capture range of a light ray of a green pixel.

FIG. 11 is a diagram showing MTF characteristics with respect to a horizontal spatial frequency component of a pixel 100g.

FIG. 12 is a diagram showing the MTF of a rectangular aperture pixel.

FIG. 13 is a diagram showing an MTF of an optical low pass filter.

FIG. 14 shows an F number of 4.0 and a wavelength of an object image of 550.
It is a figure which shows the MTF characteristic of an stigmatic lens when nm is assumed.

FIG. 15 is a diagram showing a total MTF of the image forming lens and the pixel of the image sensor when the pixel 100g is used.

FIG. 16 is a diagram showing a total MTF of pixels of an imaging lens, an optical low-pass filter, and an image sensor when using conventional pixels.

FIG. 17 is a diagram showing a total MTF when a conventional pixel does not use an optical low-pass filter.

FIG. 18 is a diagram showing a configuration of a dichroic film.

FIG. 19 is a diagram showing characteristics of a dichroic film.

FIG. 20 is a simplified diagram showing characteristics of a dichroic film.

FIG. 21 is a simplified diagram showing characteristics when reflected by a G transmission dichroic film and transmitted by a B transmission dichroic film.

FIG. 22 is a simplified diagram showing characteristics when reflected by a G transmission dichroic film and transmitted by an R transmission dichroic film.

FIG. 23 is a simplified diagram showing characteristics when reflected by an R transmission dichroic film and transmitted by a G transmission dichroic film.

FIG. 24 is a simplified diagram showing characteristics when reflected by a B transmission dichroic film and transmitted by a G transmission dichroic film.

FIG. 25 is a diagram showing a second exemplary embodiment of the present invention.

FIG. 26 is a ray trace diagram (reflected light) according to the second embodiment of the present invention.

FIG. 27 is a ray trace diagram (transmitted light) according to the second embodiment of the present invention.

FIG. 28 is a diagram showing a third exemplary embodiment of the present invention.

FIG. 29 is a ray trace diagram (reflected light) according to the third embodiment of the present invention.

FIG. 30 is a ray trace diagram (transmitted light) according to the third embodiment of the present invention.

FIG. 31 is a diagram showing a fourth exemplary embodiment of the present invention.

FIG. 32 is a ray trace diagram (reflected light) according to the fourth embodiment of the present invention.

FIG. 33 is a ray trace diagram (transmitted light) according to the fourth embodiment of the present invention.

FIG. 34 is a diagram illustrating an imaging device.

FIG. 35 is a cross-sectional view showing a conventional pixel structure.

FIG. 36 is a plan view showing a conventional image sensor.

FIG. 37 is a diagram illustrating characteristics of a conventional color filter.

[Explanation of symbols]

1 Silicon Wafer 2 Microlens 3 Photoelectric Converter 4 Wavelength Selector 4g Green Transmission Wavelength Selector 4r Red Transmission Wavelength Selector 5 Second Refractive Index Region 6 First Refractive Index Region 7 Fifth Refractive Index Region 8 Third refractive index area 9 Fourth refractive index area 10 Poly wiring layer 11 AL1 wiring layer 12 AL2 wiring layer 13 AL3 wiring layer 14 Flattening layer 41 Color filter 41g Green color filter 41r Red color filter 61 Image sensor (conventional) 61mnr Red pixel 61mng, 61mng2 Green pixel 61mnb Blue pixel 91 Effective pixel aperture 92 Effective pixel aperture (reflected light) 100 Image sensor 100g, 200g, 300g, 400g Green pixel 100r, 101r, 200r, 201r, 300r,
301r, 400r, 401r Red pixels 110, 120, 130, 140 Object light 301 Monochromatic image sensor 305 Dichroic film 305a Green light reflecting dichroic film 305b Blue light reflecting dichroic film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 5/335 H04N 5/335 V H01L 27/14 DF term (reference) 2H042 CA12 CA17 2H048 BA04 BB02 BB07 BB46 4M118 AA01 AA05 AB01 BA08 BA14 CA34 FA06 GA09 GB04 GB07 GB11 GB15 GC08 GC11 GC14 GC17 GC20 GD04 GD07 5C024 CY49 EX22 EX24 EX43 EX51 GY01

Claims (12)

[Claims] 1. A photoelectric conversion unit, a wavelength selection unit formed on the light incident side of the photoelectric conversion unit and transmitting light in a predetermined wavelength range, and formed on the light incident side of the wavelength selection unit. A first region having a predetermined refractive index and a second region having a predetermined refractive index formed on the light incident side of the first region, and the first region An image sensor, wherein the refractive index of the area is higher than the refractive index of the second area. 2. The third region according to claim 1, which is provided between the wavelength selection unit and the photoelectric conversion unit and has a predetermined refractive index, and is provided in a peripheral portion of the third region. And a fourth region having a predetermined refractive index, wherein the third region has a higher refractive index than the fourth region. 3. The device according to claim 2, further comprising a fifth region having a predetermined refractive index formed between the third region and the wavelength selection unit, wherein the third region has a refractive index of , The fifth
An image sensor having a refractive index higher than that of the region. 4. The image pickup device according to claim 1, wherein the second region is a microlens that collects light. 5. The image pickup device according to claim 1, further comprising a microlens for collecting light on the second region. 6. The image pickup device according to claim 4, wherein a surface where the microlens and the second region contact each other has a curvature. 7. The device according to claim 3, wherein the fifth region is
An image pickup device having a structure having a slope from a central portion toward a peripheral portion. 8. The method according to claim 3, wherein the fifth region is
An image pickup device having a square cone shape. 9. The image pickup device according to claim 1, wherein the wavelength selection unit has a sloped surface from a central portion toward a peripheral portion. 10. The image pickup device according to claim 1, wherein the wavelength selection unit has a shape of a square cone. 11. The image pickup device according to claim 9, wherein the wavelength selection unit transmits light in the first wavelength range and reflects light in the second wavelength range. 12. The image sensor according to claim 1, an analog / digital converter that converts a signal from the image sensor into a digital signal, and a signal from the analog / digital converter. And a signal processing circuit for processing the image pickup device.