Optical element, imaging element, and imaging device

Abstract

An optical element array (120) has a transparent layer (150) for covering pixels (130) which include photoelectric conversion elements, and a plurality of columnar structures (160) which are arranged on the transparent layer (150) or in the transparent layer (150) in the surface direction of the transparent layer (150) and which guide incident light to the corresponding photoelectric conversion elements, the plurality of columnar structures (160) being formed on the entire surface of the transparent layer (150) at intervals shorter than the wavelength of the incident light.

Description

[Technical field]

[0001] The present invention relates to an optical element, an imaging element, and an imaging apparatus. [Background technology]

[0002] A typical imaging device uses a lens optical system and a two-dimensional imaging element such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor to obtain a two-dimensional image consisting of light intensity information and color information from the object to be imaged.

[0003] In an imaging device, in order to perform color separation of incident light on each pixel including a photoelectric conversion element, a color filter corresponding to each pixel is provided on a pixel array having pixels including photoelectric conversion elements arranged in a two-dimensional array. In order to improve sensitivity characteristics, the imaging device forms an on-chip microlens (hereinafter, referred to as an on-chip lens) on the color filter, and the incident light is focused on the photoelectric conversion element by the on-chip lens. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-084608 A Summary of the Invention [Problem to be solved by the invention]

[0005] 25 and 26 are plan views of an on-chip lens. As shown in Fig. 25 and Fig. 26, an on-chip lens 220 or an on-chip lens 320 is formed on each of the pixels 200R, 200G, and 200B of the pixel array 210. However, there are gaps 220E, 320E, etc. between the on-chip lenses 220 and between the on-chip lenses 320. Since light incident outside the lens opening region such as the gaps 220E, 320E between the lenses cannot be effectively collected on the photoelectric conversion element, the conventional on-chip lenses 220 and 320 cannot receive all the incident light, and the light receiving efficiency is limited.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide an optical element, an imaging element, and an imaging apparatus that can improve light receiving efficiency compared to the prior art. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the optical element of the present invention has a transparent layer for covering pixels including photoelectric conversion elements, and a plurality of columnar structures arranged in the plane direction of the transparent layer on or within the transparent layer and directing incident light to corresponding photoelectric conversion elements, wherein the plurality of columnar structures are formed over the entire surface of the transparent layer at intervals shorter than the wavelength of the incident light.

[0008] An image pickup device according to the present invention includes the optical element described above and a plurality of pixels each including a photoelectric conversion element.

[0009] An imaging device according to the present invention includes the imaging element described above, and a signal processing unit that processes an electrical signal output by the imaging element to generate an image. Effect of the Invention

[0010] According to the present invention, it is possible to provide an imaging element and an imaging device that can improve light receiving efficiency compared to the conventional art. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a side view showing a schematic configuration of an imaging device according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a schematic view of a part of a cross section of a pixel array and a polarized wavelength separation lens array of an image sensor according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing a schematic view of a part of a cross section of a pixel array and an optical element array in a central portion of an image sensor according to an embodiment. [Figure 4] FIG. 4 is a diagram showing a schematic view of a part of a cross section of a pixel array and an optical element array in a peripheral portion of an image sensor according to an embodiment. [Diagram 5] FIG. 5 is a top view of an optical element array in the center of an image sensor according to an embodiment. [Figure 6] FIG. 6 is a diagram showing the minimum structural height and maximum aspect ratio of a conventional organic approximation structure and a columnar structure according to the embodiment. [Figure 7] FIG. 7 is a side view of the columnar structure. [Figure 8] FIG. 8 is a plan view of the columnar structure. [Figure 9] FIG. 9 is a diagram showing the relationship between the width of a columnar structure and the light transmittance. [Figure 10] FIG. 10 is a diagram showing the relationship between the width of a columnar structure and the phase characteristics of light from the columnar structure. [Figure 11] FIG. 11 is a diagram for explaining the definition of the incident angle. [Figure 12] FIG. 12 is a diagram showing a phase distribution targeted by the lens design when light is incident at an incident angle of θ=0°, φ=0°, and a lens pattern that realizes this phase distribution. [Figure 13] FIG. 13 is a diagram showing a phase distribution targeted by the lens design when light is incident at angles of incidence of θ=45° and φ=0°, and a lens pattern that realizes this phase distribution. [Figure 14]FIG. 14 is a diagram showing a phase distribution targeted by the lens design when light is incident at angles of incidence of θ=45° and φ=45°, and a lens pattern that realizes this phase distribution. [Figure 15] FIG. 15 is a diagram showing the light-collecting intensity by the optical element unit and its wavelength dependency. [Figure 16] FIG. 16 is a diagram showing the light-collecting intensity by the optical element unit and its wavelength dependency. [Figure 17] FIG. 17 is a diagram showing the light-collecting intensity by the optical element unit and its wavelength dependency. [Figure 18] FIG. 18 is a diagram showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=0° is incident, and the incidence angle dependency of the incident light. [Figure 19] FIG. 19 is a diagram showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=0° is incident, and the incidence angle dependency of the incident light. [Figure 20] FIG. 20 is a diagram showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=0° is incident, and the incidence angle dependency of the incident light. [Figure 21] FIG. 21 is a diagram showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=45° is incident, and the incidence angle dependency of the incident light. [Figure 22] FIG. 22 is a diagram showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=45° is incident, and the incidence angle dependency of the incident light. [Figure 23] FIG. 23 is a diagram showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=45° is incident, and the incidence angle dependency of the incident light. [Figure 24] FIG. 24 is a diagram illustrating another example of a portion of a cross section of a pixel array and an optical element array in an image sensor according to an embodiment. [Diagram 25] FIG. 25 is a plan view of the on-chip lens. [Figure 26] FIG. 26 is a plan view of the on-chip lens. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The best mode for carrying out the present invention will be described in detail below with reference to the drawings. Note that in the following description, each drawing merely shows the shape, size, and positional relationship in a schematic manner to the extent that the contents of the present invention can be understood, and therefore the present invention is not limited to only the shape, size, and positional relationship exemplified in each drawing. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals.

[0013] [Embodiment Mode] [Imaging device] First, an imaging device according to an embodiment of the present invention will be described below. Fig. 1 is a side view showing a schematic configuration of an imaging device according to an embodiment.

[0014] 1, an imaging device 10 according to an embodiment includes a lens optical system 11, an imaging element 12, and a signal processing unit 13. The imaging element 12 includes a photoelectric conversion element such as a CCD or a CMOS. The signal processing unit 13 processes a photoelectric conversion signal output from the imaging element 12 to generate an image signal.

[0015] Natural light, illumination light, or other light is irradiated onto object 1, and the light transmitted / reflected / scattered by object 1 or emitted from object 1 forms an optical image on image sensor 12 by lens optical system 11. Generally, lens optical system 11 is composed of a lens group made up of multiple lenses lined up along an optical axis to correct various optical aberrations, but in Fig. 1 it is shown as a single lens for the sake of simplicity. Signal processing unit 13 has an image signal output that sends the generated image signal to the outside.

[0016] The imaging device 10 may include known components such as an infrared light blocking optical filter, an electronic shutter, a viewfinder, a power source (battery), a flashlight, etc., but the description of these components is omitted because they are not particularly necessary for understanding the present invention. Also, the above configuration is merely an example, and in the embodiment, known elements can be used in appropriate combination as components other than the lens optical system 11, the imaging element 12, and the signal processing unit 13.

[0017] [Image sensor] Next, an outline of the imaging element 12 according to the embodiment will be described. FIG. 2 is a diagram showing a cross section of the lens optical system 11 and the main part of the imaging element 12 according to the embodiment. In FIG. 2 and subsequent figures, a part of the imaging element 12 will be described as the imaging element 100. The imaging element 100 has an optical element array (optical element) in which optical elements each consisting of a plurality of columnar structures that guide incident light to a photoelectric conversion element of a pixel array are formed on the entire surface of a color filter. As shown in FIG. 2, in the imaging element 100, since the incidence angle θ of light incident on the imaging element 100 from the lens optical system 11 differs between the central part and the outer periphery, the plurality of columnar structures formed on the optical element array are set to a size that gives a phase characteristic for guiding the incident light to the photoelectric conversion element directly below according to the incidence angle. Hereinafter, the structure of the imaging element 100 will be described with reference to FIGS. 3 to 5.

[0018] Fig. 3 is a diagram showing a part of a cross section of a pixel array and an optical element array in a central part of an image sensor according to an embodiment. Fig. 4 is a diagram showing a part of a cross section of a pixel array and an optical element array in a peripheral part of an image sensor according to an embodiment. Fig. 5 is a top view of an optical element array in a central part of an image sensor according to an embodiment.

[0019] 3 and 4, the image sensor 100 has a pixel array 110 and an optical element array 120 arranged opposite to the pixel array 110. The optical element array 120 is arranged on the side where light from the lens optical system 11 is incident. The optical element array 120 is formed on the upper surface of a transparent layer 150 formed on the pixel array 110. A color filter 170 corresponding to each pixel is provided on the pixel array 110. The transparent layer 150 is a transparent layer with a low refractive index made of a material such as SiO2 (refractive index n=1.45).

[0020] The pixel array 110 has a wiring layer 180 and pixels 130 including photoelectric conversion elements arranged in a two-dimensional array. The pixels 130 of the pixel unit 140L receive, for example, G light, and the pixels 130 of the pixel unit 140R receive R light.

[0021] In the optical element array 120, optical elements each composed of a plurality of columnar structures 160 that guide incident light to a photoelectric conversion element of a corresponding pixel 130 directly below are arranged in a two-dimensional array. For example, FIG. 5 shows a case in which the wavelength regions separated by the color filter 170 are red (R), green (G), and blue (B). In the optical element array 120 in FIG. 5, an R pixel unit that receives R light, two G pixel units that receive G light, and a B pixel unit that receives B light on the pixel array 110 are arranged directly below each other, and an optical element unit is formed on the two-dimensional array, with a set of optical element units each composed of an optical element unit 120R (optical element) corresponding to the R pixel unit, two optical element units 120G (optical element) corresponding to the G pixel unit, and an optical element unit 120B (optical element) corresponding to the B pixel unit.

[0022] The multiple columnar structures 160 are formed using a material having a refractive index higher than that of the surrounding materials (transparent layer 150, air). This allows the columnar structures 160 to strongly confine light within the columnar structures and prevent optical coupling with adjacent columnar structures. The columnar structures 160 are formed using, for example, SiN (refractive index n=2.05) or TiO2 (refractive index n=2.4).

[0023] As shown in Figs. 3 and 4, the plurality of columnar structures 160 are formed at the same height when viewed from the side. The plurality of columnar structures 160 are formed on the entire surface of the optical element array 120 at intervals shorter than the wavelength of the incident light. As shown in Fig. 5, the optical element units 120R, 120G, and 120B have the plurality of columnar structures 160 formed in a lattice shape when viewed from above. The plurality of columnar structures 160 are rectangular columns. Note that the example in Fig. 5 is just an example, and the columnar structures may be structures that are four-fold symmetrical in plan view, such as a hollow square, a circle, a hollow circle, or a cross.

[0024] The plurality of columnar structures 160 are each formed to have a width w having phase characteristics for guiding incident light to a photoelectric conversion element of a corresponding pixel 130 directly below according to the incident angle of the incident light on each columnar structure when viewed in a plan view. Each of the plurality of columnar structures 160 imparts an amount of optical phase delay to the incident light according to the width of the columnar structure 160 when viewed in a plan view.

[0025] In the optical element units 120R, 120G, and 120B, each of the plurality of columnar structures 160 constituting the optical element units 120R, 120G, and 120B has a width that provides an optical phase delay distribution for guiding incident light to each photoelectric conversion element of the corresponding R pixel unit, G pixel unit, and B pixel unit. In the optical element units 120R, 120G, and 120B, the width of each of the plurality of columnar structures 160 constituting the optical element units 120R, 120G, and 120B when viewed in plan is set to a width that provides an optical phase delay distribution for guiding incident light to the photoelectric conversion element directly below the optical element units 120R, 120G, and 120B according to the incident angle of the incident light. The optical phase delay distribution is an optical phase delay for collecting light.

[0026] The image sensor 100 realizes a lens function by forming columnar structures 160, which have the same height but gradually change width, over the entire surface of the optical element array 120. Since each columnar structure 160 behaves like a columnar optical waveguide, in the image sensor 100, by changing the width of the columnar structure 160, the effective refractive index of the columnar structure 160 can be changed, and the phase of the transmitted light can be freely controlled.

[0027] In other words, each columnar structure 160 behaves as a sub-wavelength optical waveguide, and there is almost no optical coupling with adjacent columnar structures 160 due to optical confinement, so that by designing the width w of each columnar structure 160 in a plan view for each columnar structure 160, it is possible to give different optical characteristics (e.g., phase delay characteristics) to each of the multiple columnar structures 160. By making the spatial distribution of this phase delay amount equivalent to that of a (Fresnel) lens, it is possible to impart a lens function to the columnar structures 160.

[0028] Here, Non-Patent Document 1 describes that a structure made of a low refractive index material such as SiO2 is made to function as a lens.

[0029] In Non-Patent Document 1, an approximation is described that when the structure is very small compared to the wavelength, the effective refractive index of the structure can be expressed as approximately the average value of the refractive index of the structural lens and the surrounding material. However, when the difference between the refractive index of the structure and the surrounding refractive index is large and the size of the structure is on the order of sub-wavelength, this approximation cannot be applied because the light is confined inside the structure and excites the optical waveguide mode or the resonance mode. For this reason, the structure described in Non-Patent Document 1 is limited to a combination of materials with a small refractive index difference, such as SiO2 as the material and air as the surrounding material, and the aspect ratio of the structure becomes large.

[0030] In contrast, in the image sensor 100, each columnar structure 160 is formed using a high refractive index material such as SiN or TiO2. Therefore, the minimum height of the columnar structures 160 required to achieve a phase change amount of 0 to 2π is lower than that of structures made of low refractive index materials such as SiO2 (see Non-Patent Document 1). Therefore, in the image sensor 100, the minimum structural height required for phase control of 0 to 2π is relatively small, and a lens function can be achieved by the columnar structures 160 with a low aspect ratio that are easy to fabricate.

[0031] The plurality of columnar structures 160 are prisms with square bottoms. In this way, in the image sensor 100, each columnar structure 160 is made to have a four-fold rotationally symmetric structure, such as a square, when viewed in plan, thereby making the image sensor 100 independent of polarization. Note that it is clear from the theoretical formula that the structure described in Non-Patent Document 1 has polarization dependency in the effective refractive index.

[0032] Furthermore, Non-Patent Document 1 describes a structure having curved surfaces and steps. In contrast, each columnar structure 160 in the present embodiment is a binary pattern of a rectangular column without steps. Therefore, in the imaging element 100, curved surfaces and steps can be eliminated from the cross section of the columnar structure, and therefore, compared to the structure described in Non-Patent Document 1, it is relatively easy to create the columnar structure 160.

[0033] Furthermore, the imaging element 100 realizes a lens function by forming a plurality of columnar structures 160 all over the optical element array 120, so that all incident light can be received and the lens aperture can be maximized.

[0034] Moreover, each of the columnar structures 160 is formed to have a width w having phase characteristics for guiding light to a photoelectric conversion element of the pixel 130 directly below in accordance with the angle of incidence of the light incident on each of the columnar structures 160 when viewed in a plan view. That is, in the image sensor 100, it is possible to optimize the structural pattern of the columnar structures 160 for each pixel in accordance with the main angle of incidence in order to improve the light receiving efficiency. In other words, in the image sensor 100, the shape pattern of the columnar structures 160 in a plan view is optimized in accordance with the angle of incidence θ of light incident on each of the columnar structures 160.

[0035] This allows the columnar structures 160 to focus light onto the photoelectric conversion elements of the pixels 130 directly below in both the outer periphery (see FIG. 4) where light is incident at a large incident angle θ and the center (see FIG. 3) where light is incident perpendicularly. Therefore, the image sensor 100 can focus a large amount of light onto the photoelectric conversion elements directly below, and can generate image signals with uniform brightness throughout the entire image sensor 100.

[0036] [Height of the columnar structure] Next, the height of the columnar structure 160 when viewed from the side will be described. Hereinafter, the height of the columnar structure 160 when viewed from the side will be referred to as the height of the columnar structure 160. And the width of the columnar structure 160 when viewed in plan view will be referred to as the width of the columnar structure 160. Here, the minimum height of the columnar structure 160 required for phase control of 0 to 2π will be described.

[0037] The phase delay amount φ caused by the columnar structure 160 is expressed by Equation (1), where λ is the wavelength of light in vacuum, h is the height of the columnar structure 160, and n is the effective refractive index of the columnar structure 160 eff , and n0 is the refractive index of the surrounding material.

[0038] [Equation number]

[0039] Equation (1) is applicable to both the columnar structure 160 in the imaging device 100 and the structure described in Non-Patent Document 1 (hereinafter referred to as the effective medium approximation structure).

[0040] In the case of the effective medium approximation structure, the effective refractive index n eff is known to be determined by the area ratio of the structure to the surrounding material. In the case of the effective medium approximation structure, the value of n eff also varies depending on the polarization. And in the case of the columnar structure 160, since the optical waveguide mode greatly depends on the width of the columnar structure 160, the effective refractive index n eff is known to be expressed as a function of the width w of the columnar structure 160. In both the case of the effective medium approximation structure and the columnar structure 160, n0 < n eff < n1. Note that n1 is the refractive index of the material constituting the structure.

[0041] Therefore, in order to control the phase change amount between 0 and 2π, the height of the structure needs to be expressed by Equation (2).

[0042] [Equation number]

[0043] Fig. 6 is a diagram showing the minimum structural height and maximum aspect ratio of an organic approximation structure in the prior art and the columnar structure 160 in the embodiment. In Fig. 6, the maximum aspect ratio is calculated assuming that the minimum structural width is 100 nm when the wavelength of light is 635 nm.

[0044] To apply the effective medium approximation, n1-n0 needs to be small. Therefore, in the case of an effective medium approximation structure, the required height of the structure is inevitably high at 1411 nm as shown in Figure 6, which is several wavelengths.

[0045] On the other hand, in the case of the columnar structure 160, a larger n1 is preferable from the viewpoint of light confinement, so the value of n1-n0 is larger than that of the effective medium approximation structure. For example, the materials forming the columnar structure 160 are SiN (n=2.05) and TiO2 (n=2.4), and n1-n0≧0.7.

[0046] As a result, the required structural height of the columnar structure 160 is relatively lower than that of the effective medium approximation structure, and is generally one wavelength or less, as shown in Fig. 6. In this manner, the aspect ratio of the columnar structure 160 is lower than that of the effective medium approximation structure.

[0047] [Columnar structure] An example of the structure of the columnar structures 160 will be described. FIG. 7 is a side view of the columnar structures 160. FIG. 8 is a plan view of the columnar structures 160. As shown in FIGS. 7 and 8, for example, the columnar structures 160 are formed on the upper surface of a transparent layer 150u made of quartz. The height (length in the z-axis direction) of the columnar structures 160 is h=1000 nm, and the arrangement period of the columnar structures 160 is 320 nm. The width w of the columnar structures 160 is set corresponding to the phase to be controlled, which is between 0 and 2π.

[0048] Fig. 9 is a diagram showing the relationship between the width w of the columnar structure 160 and the light transmittance. Fig. 10 is a diagram showing the relationship between the width w of the columnar structure 160 and the light phase characteristics of the columnar structure 160.

[0049] As shown in Fig. 9, even when the width w of the columnar structure 160 is changed between 100 and 240 nm, a high transmittance can be maintained. By adjusting the width w of the columnar structure 160 between 100 and 240 nm, the phase of light passing through the columnar structure 160 can be controlled to a desired phase between 0 and 2π. In Figs. 9 and 10, even when the width of the columnar structure 160 is reduced to 100 nm, the maximum aspect ratio of the columnar structure 160 can be suppressed to 10.

[0050] [Lens design] In the image sensor 100 according to this embodiment, the phase distribution of the columnar structures 160 functioning as lenses is designed to focus light on the centers of the pixels 130 below the optical element array 120 in accordance with the incident angle. Then, in the image sensor 100, the width w of each columnar structure 160 is set with reference to the phase characteristics in Fig. 10 so as to achieve the designed phase distribution, thereby realizing an ideal phase distribution as a design target.

[0051] For example, the parameters of a design example are shown below. Size of one photoelectric conversion element = Lens area: 3.2 μm × 3.2 μm Focal length: 3.2μm Design wavelength: 520nm

[0052] Fig. 11 is a diagram for explaining the definition of the incident angle. As shown in Fig. 11, a case where light is incident at an incident angle of (θ, φ) will be explained. The phase distribution φ of a lens that focuses light at an incident angle (θ, φ) at a focal length f to a point directly below the center of the lens (columnar structure 160) is expressed by the following formula (3).

[0053]

number

[0054] In equation (3), λ d is the design wavelength, f is the focal length, and n in is the refractive index of the material on the incident side, and n out is the refractive index of the material on the exit side, and C is an arbitrary constant.

[0055] For example, f = 3.2 μm, n in = 1.0 (air), n out = 1.445 (quartz glass). φ is converted so as to fall within the range of 0 to 2π. For example, if φ is -0.5π, it is converted to 1.5π, and if φ is 2.5π, it is converted to 0.5. With this setting, the phase distribution of the lens design target when light is incident at an arbitrary incident angle and the lens (columnar structure 160) pattern that can realize this phase distribution will be described with reference to Figs. 12 to 14. The phase distribution of the lens design target is the phase distribution of a lens that focuses light at a certain incident angle at a point directly below the center of the lens with a focal length f.

[0056] Fig. 12 is a diagram showing a phase distribution of a lens design target when light is incident at an incident angle of θ=0°, φ=0°, and a lens (columnar structure 160) pattern that realizes the phase distribution. Fig. 13 is a diagram showing a phase distribution of a lens design target when light is incident at an incident angle of θ=45°, φ=0°, and a lens pattern that realizes the phase distribution. Fig. 14 is a diagram showing a phase distribution of a lens design target when light is incident at an incident angle of θ=45°, φ=45°, and a lens pattern that realizes the phase distribution. Fig. 12(1), Fig. 13(1), and Fig. 14(1) show the phase distribution of a lens design target when light is incident at an incident angle of each condition. Figures 12(2), 13(2), and 14(2) are plan views of columnar structures 160 that can realize the phase distributions of Figures 12(1), 13(1), and 14(1), respectively, and are shape patterns of columnar structures 160 designed per pixel.

[0057] As shown in Fig. 12(2), Fig. 13(2), and Fig. 14(2), the columnar structure 160 is a prism with a square bottom surface. The width w of the columnar structure 160 is set to a width that can realize the phase at the corresponding position in the phase distribution of Fig. 12(1), Fig. 13(1), and Fig. 14(1), based on the relationship between the width w of the columnar structure 160 and the phase characteristic of the light of the columnar structure 160 shown in Fig. 10.

[0058] For example, the optical element unit 120-1 shown in Fig. 12(2) is a shape pattern of the columnar structure 160 that realizes the phase distribution of the lens design target when light is incident at an incident angle of θ=0°, φ=0°. The optical element unit 120-2 shown in Fig. 13(2) is a shape pattern of the columnar structure 160 that realizes the phase distribution of the lens design target when light is incident at an incident angle of θ=45°, φ=0°. The optical element unit 120-3 shown in Fig. 14(2) is a shape pattern of the columnar structure 160 that realizes the phase distribution of the lens design target when light is incident at an incident angle of θ=45°, φ=45°.

[0059] [Wavelength dependence of focused light intensity] In the embodiment, as in the optical element units 120R, 120G, and 120B shown in Fig. 5, the pattern of each columnar structure 160 of the optical element units 120R, 120G, and 120B is designed to correspond to the design wavelength of the photoelectric conversion element of the pixel unit immediately below the corresponding optical element unit. In the optical element unit, the width w of each of the plurality of columnar structures 160 forming the optical element unit in plan view is set to a width that gives an optical phase delay amount distribution for guiding light in a wavelength range received by the photoelectric conversion element corresponding to the optical element unit to the photoelectric conversion element corresponding to the optical element unit. Here, the wavelength dependency of the light collection intensity by the optical element array 120 will be described.

[0060] Fig. 15 to Fig. 17 are diagrams showing the light-collecting intensity by the optical element unit and its wavelength dependency. Fig. 15 corresponds to B light with a wavelength λ=450 nm, Fig. 16 corresponds to G light with a wavelength λ=520 nm, and Fig. 17 corresponds to R light with a wavelength λ=635 nm.

[0061] FIG. 15(1), FIG. 16(1), and FIG. 17(1) show patterns of lenses (columnar structures 160) optimally designed for vertically incident light (θ=0°, φ=0°), and the average of both polarizations is taken. FIG. 15(2), FIG. 16(2), and FIG. 17(2) show the light-collecting intensity by the optical element units 120-4, 120-5, and 120-6 of FIG. 15(1), FIG. 16(1), and FIG. 17(1). The light-collecting intensity is the total intensity within the light-collecting spot width (λ / NA, NA is the numerical aperture of the lens) on the photoelectric conversion element surface of the pixel 130. FIG. 15(3), FIG. 16(3), and FIG. 17(3) show the wavelength dependency of the light-collecting intensity by the optical element units 120-4, 120-5, and 120-6.

[0062] 15(3), 16(3), and 17(3), it can be seen that in any of the optical element units 120-4, 120-5, and 120-6, 96% or more of light is transmitted through the structure and can be received by the pixel 130. In addition, the light collecting intensity of the optical element units 120-4, 120-5, and 120-6 is maximum around the design wavelength.

[0063] Therefore, in the image sensor 100, it is possible to design light collection that matches each design wavelength simply by changing the pattern of the columnar structures 160, such as the optical element units 120-4, 120-5, and 120-6, in correspondence with each color band (the transmission bands of the R, G, and B color filters). In the image sensor 100, the design wavelength of each pixel 130 is determined in accordance with the color filter on the pixel 130, and the optical element units 120-4, 120-5, and 120-6 are integrated in accordance with the design wavelength of the pixel 130 directly below.

[0064] [Design example of optical element unit according to incident angle] In this embodiment, the pattern of each columnar structure 160 of the optical element unit is designed according to the incident angle of the incident light. In the optical element unit, the width w of each of the plurality of columnar structures 160 forming the optical element unit in plan view is set to a width that provides an optical phase delay amount distribution for guiding the incident light to the photoelectric conversion element directly below the optical element unit according to the incident angle of the incident light. Therefore, a design example of the optical element unit corresponding to the incident angle of the incident light to the optical element array 120 will be described.

[0065] 18 to 20 are diagrams showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) with φ=0° is incident and the incidence angle dependency of the incident light. FIG. 18(1) is a pattern of the columnar structure 160 optimally designed for incident light with θ=15°, φ=0°, FIG. 19(1) is a pattern of the columnar structure 160 optimally designed for incident light with θ=30°, φ=0°, and FIG. 20(1) is a pattern of the columnar structure 160 optimally designed for incident light with θ=45°, φ=0°, and the average of both polarizations is taken. FIG. 18(2), FIG. 19(2), and FIG. 20(2) are diagrams showing the light collection intensity by the optical element units 120-7, 120-8, and 120-9 of FIG. 18(1), FIG. 19(1), and FIG. 20(1). FIG. 18(3), FIG. 19(3), and FIG. 20(3) are diagrams showing the incidence angle dependence of the light-collecting intensity by the optical element units 120-7, 120-8, and 120-9.

[0066] As shown in FIG. 18(3), FIG. 19(3), and FIG. 20(3), all of the optical element units 120-7, 120-8, and 120-9 exhibit maximum light collection intensity around the designed incident angle.

[0067] 21 to 23 are diagrams showing the light collection intensity by the optical element unit when parallel light (λ=520 nm) of φ=45° is incident and the incidence angle dependency of the incident light. FIG. 21(1) is a pattern of the columnar structure 160 optimally designed for incident light of θ=15°, φ=45°, FIG. 22(1) is a pattern of the columnar structure 160 optimally designed for incident light of θ=30°, φ=45°, and FIG. 23(1) is a pattern of the columnar structure 160 optimally designed for incident light of θ=45°, φ=45°, and both polarizations are averaged. FIG. 21(2), FIG. 22(2), and FIG. 23(2) are diagrams showing the light collection intensity by the optical element units 120-10, 120-11, and 120-12 of FIG. 21(1), FIG. 22(1), and FIG. 23(1). FIG. 21(3), FIG. 22(3), and FIG. 23(3) are diagrams showing the incidence angle dependence of the light-collecting intensity by the optical element units 120-10, 120-11, and 120-12.

[0068] As shown in FIG. 21(3), FIG. 22(3), and FIG. 23(3), each of the optical element units 120-10, 120-11, and 120-12 exhibits a maximum light collection intensity around the designed incident angle.

[0069] In the imaging element 100, by arranging the optical element units 120-7 to 120-12 described above in accordance with the incident angle (θ, φ) of the incident light, it becomes possible to focus light with high intensity on the photoelectric conversion element of the pixel 130 directly below.

[0070] [Effects of the embodiment] In this manner, in the imaging element 100 of the embodiment, a lens function is realized by forming a plurality of columnar structures 160 over the entire surface of the optical element array 120 at intervals shorter than the wavelength of the incident light, so that all incoming light can be received, thereby improving the light receiving efficiency.

[0071] In addition, in the image sensor 100, the multiple columnar structures are each formed to have a width having phase characteristics for guiding light incident on each columnar structure to a photoelectric conversion element directly below in accordance with the angle of incidence of the light when viewed in a plan view, and are formed to have the same height when viewed from the side. In the image sensor 100, the multiple columnar structures 160 can realize lens characteristics corresponding to the angle of incidence for each pixel 130, so that an image signal having uniform brightness can be generated throughout the entire image sensor 100.

[0072] Furthermore, the imaging element 100 uses, as lenses, a plurality of columnar structures 160 in a binary pattern having a quadrangular prism shape made of a material having a refractive index higher than that of the surrounding material. Therefore, the plurality of columnar structures 160 used as lenses by the imaging element 100 have a lower aspect ratio and a simpler configuration than the structures described in Non-Patent Document 1, and are therefore easier to fabricate.

[0073] The optical element unit is not limited to the above configuration, and may have various forms in terms of the number, interval, structural shape, and arrangement pattern. The columnar structures 160 may be connected to each other, or may be embedded in a transparent material.

[0074] 3 and 4, the optical element array 120 is formed on the upper surface of the transparent layer 150, but this is not limited thereto. Fig. 24 is a diagram showing another example of a part of a cross section of a pixel array and an optical element array in an image sensor according to an embodiment. As shown in the image sensor 100A in Fig. 24, the optical element array 120A is formed on the bottom surface of an independent transparent substrate 190. In this manner, a plurality of columnar structures 160 may be formed inside the transparent layer 150A (e.g., air).

[0075] Further, in the above embodiment, four pixels are positioned directly below one optical element unit, but the present invention is not limited to this.

[0076] In the embodiment, the columnar structure 160 is made of SiN or TiO2, but is not limited thereto. For example, when the image sensor 100, 100A is used in the visible light to near-infrared light region with a wavelength of 380 nm to 1000 nm, materials such as SiN, SiC, TiO2, and GaN are suitable for the material of the columnar structure 160 because they have a high refractive index and low absorption loss. When the image sensor 100, 100A is used in the near-infrared light region with a wavelength of 800 to 1000 nm, materials such as Si, SiC, SiN, TiO2, GaAs, and GaN are suitable for the material of the columnar structure 160 with low loss for such light. Furthermore, in the long-wavelength near-infrared region (such as 1.3 μm and 1.55 μm, which are communication wavelengths), in addition to the above-mentioned materials, InP or the like can be used as the material of the columnar structure 160.

[0077] When forming the micro-spectroscopic element of the columnar structure 160 by pasting and applying, examples of materials include polyimides such as fluorinated polyimide, BCB (benzocyclobutene), photocurable resins, UV epoxy resins, acrylic resins such as PMMA, and polymers such as general resists.

[0078] Similarly, in the embodiment, an example was shown in which SiO2 and an air layer were assumed as the material of the transparent layers 150 and 150A, but this is not limited thereto. The material of the transparent layers 150 and 150A may be a general glass material, SiO2, an air layer, or the like, as long as it has a refractive index lower than that of the material of the columnar structure 160 and has low loss with respect to the wavelength of the incident light. In addition, the transparent layers 150 and 150A may be transparent layers having a laminated structure made of multiple materials.

[0079] In the embodiment, the light in the wavelength range corresponding to the columnar structure 160 is the three primary colors of R, G, and B, but at least one of the three wavelength ranges may be light of a wavelength other than the three primary colors (for example, infrared light or ultraviolet light).

[0080] In the optical element arrays 120 and 120A, the width of at least a part of the plurality of columnar structures 160 in plan view is set to a width that provides an optical phase delay distribution for guiding incident light to the corresponding photoelectric conversion element directly below, based on the relationship between the width of the columnar structure 160 and the phase characteristic of light as illustrated in FIG. 10. In this way, the optical element arrays 120 and 120A realize lens characteristics corresponding to the incident angle and the wavelength range of the photoelectric conversion element for each pixel 130. Not limited to this, in this embodiment, the plurality of columnar structures 160 may have a refractive index that has a phase characteristic for guiding the light to the photoelectric conversion element directly below, depending on the incident angle of the incident light to each columnar structure. In other words, in this embodiment, the plurality of columnar structures 160 are set to have different refractive indices from each other, so that lens characteristics corresponding to the incident angle and the wavelength range of the photoelectric conversion element for each pixel 130 can be realized. In addition, in this embodiment, by changing the width of the columnar structures 160 in a planar view and the refractive index of the columnar structure 160 for each columnar structure, it is possible to realize lens characteristics corresponding to the angle of incidence and the wavelength range of the photoelectric conversion element for each pixel 130.

[0081] Moreover, the optical element arrays 120 and 120A in the present embodiment are, for example, metasurfaces. As described above, a metasurface is an element consisting of a plurality of fine structures having a width equal to or less than the wavelength of light, and may be a two-dimensional structure or a three-dimensional structure. By using a metasurface as an optical element array, the phase and light intensity can be controlled according to the characteristics of light (wavelength, polarization, and incident angle) simply by changing the parameters of the fine structures. Furthermore, when the metasurface has a three-dimensional structure, the above-mentioned design freedom increases.

[0082] While the present invention has been described above based on specific embodiments, it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0083] 1 object 10. Imaging device 11 Lens optical system 12,100,100A image sensor 13 Signal Processing Section 110 pixel array 120,120A Optical Element Array 120R, 120G, 120B, 120-1 to 120-12 Optical element unit 130 pixels 140L, 140R pixel unit 150,150A transparent layer 160 Columnar structure 170 Color Filter 180 wiring layer 190 Transparent Substrate

Claims

1. A transparent layer for covering pixels including photoelectric conversion elements; a plurality of columnar structures disposed on or within the transparent layer in a planar direction of the transparent layer and configured to guide incident light to the corresponding photoelectric conversion elements; An optical element having the plurality of columnar structures are formed on the entire surface of the transparent layer at intervals shorter than the wavelength of the incident light, The material of the columnar structure is selected from Si, SiN, SiC, TiO, etc., depending on the wavelength band of light used by the imaging element having a plurality of the pixels. ２ , GaN, GaAs, or InP; each of the plurality of columnar structures imparts to the incident light an amount of optical phase delay corresponding to a width of the columnar structure in a plan view; each of the plurality of columnar structures has a width that provides an optical phase delay distribution for guiding the incident light to the corresponding photoelectric conversion element in accordance with a design wavelength of the corresponding photoelectric conversion element and an incident angle (θ, φ) of the incident light; The θ is an angle between the z-axis, which is a normal to the xy plane of the optical element, and the incident light, when the plane of the optical element is the xy plane and the incident light is incident on the origin of the xy plane of the optical element, The optical element, wherein φ is an angle between the x-axis and a shadow of the incident light projected onto an xy plane of the optical element.

2. The optical element according to claim 1 , wherein the plurality of columnar structures are formed in a lattice pattern when viewed from above.

3. The plurality of columnar structures are a refractive index higher than a refractive index of a material surrounding the plurality of columnar structures; When viewed in a plan view, at least some of the columnar structures among the plurality of columnar structures have widths different from one another, 3. The optical element according to claim 1, wherein the optical element has the same height when viewed from the side.

4. The plurality of columnar structures are a refractive index higher than a refractive index of a material surrounding the plurality of columnar structures; At least some of the plurality of columnar structures have refractive indices different from one another, 3. The optical element according to claim 1, wherein the optical element has the same height when viewed from the side.

5. The optical element according to claim 1, characterized in that the width of each of the multiple columnar structures constituting the optical element when viewed in a planar view is set to a width that gives an optical phase delay distribution for guiding light in a wavelength range received by the photoelectric conversion element corresponding to the optical element to the photoelectric conversion element corresponding to the optical element.

6. The optical element according to claim 5 , wherein the width of each of the plurality of columnar structures in a plan view is set to a different value for each wavelength range of the corresponding photoelectric conversion element.

7. 7. The optical element according to claim 5, wherein the optical phase delay distribution is an optical phase delay for converging light.

8. 8. The optical element according to claim 1, wherein the plurality of columnar structures are formed using a material having a refractive index higher than a refractive index of the transparent layer.

9. 9. The optical element according to claim 1, wherein the plurality of columnar structures have a four-fold rotationally symmetric structure when viewed in a plan view.

10. The optical element according to any one of claims 1 to 9, A plurality of pixels each including the photoelectric conversion element; An imaging element comprising:

11. The imaging element according to claim 10; a signal processing unit that processes the electrical signal output by the imaging element to generate an image; An imaging device comprising:

Images