Image pickup element and image pickup device

Abstract

The imaging element (100) includes: a pixel array (110) formed by arranging a plurality of pixels each including a photoelectric conversion element in a two-dimensional array; and an optical element array (120) disposed opposite to the pixel array (110) and formed by arranging optical elements in a two-dimensional array. The optical elements are composed of a plurality of columnar structures (160) that guide incident light to corresponding photoelectric conversion elements. The plurality of columnar structures (160) are each formed, in a plan view, to have a width with a phase characteristic for guiding incident light corresponding to the incident angle of the incident light of each columnar structure (160) to the photoelectric conversion element directly below, and the plurality of columnar structures (160) are formed to have the same height in a side view.

Description

Technical Field

[0001] The present invention relates to an imaging element and an imaging device. Background Art

[0002] Generally, an 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 composed of intensity information and color information of light from an imaging object.

[0003] Here, the incident angle of light incident on the imaging element from the lens optical system is different between the central portion and the peripheral portion. However, since it is difficult to fabricate a lens that matches the obliquely incident light required in the peripheral portion of the sensor, there is a problem that the light reception efficiency is limited.

[0004] As a lens for solving this problem, a microstructured lens using the effective medium approximation has been proposed (for example, refer to Non-Patent Document 1). Non-Patent Document 1 describes the following approximation: when the microstructured lens is very small compared to the wavelength, the effective refractive index of the microstructured lens can be represented by the approximate average of the refractive indices of the lens and the surrounding material.

[0005] Prior Art Documents

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: Kazutoshi Onozawa, Kimiaki Toshikiyo, Takanori Yogo, Motonori Ishii, Kazuhiko Yamanaka, Toshinobu Matsuno, and Daisuke Ueda, "A MOS Image Sensor With a Digital-Microlens", IEEE transactions on electron devices, VOL.55, NO.4, 986-991(2008). Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, in a microstructured lens using the effective medium approximation, when the difference in refractive index between the lens and the surroundings is large and the size of the lens is around sub-wavelength, light is trapped inside the structure and excites waveguide modes and resonance modes, so this approximation cannot be applied. Therefore, the microstructured lens described in Non-Patent Document 1 is limited to combinations of materials with a small refractive index difference, such as SiO2 as the material and air as the surrounding material. Thus, there are the following problems: the aspect ratio of the microstructured lens becomes large, and there is polarization dependence. Furthermore, since the microstructured lens described in Non-Patent Document 1 has a structure with curves and steps, there is a problem that it is difficult to fabricate.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide an imaging element and an imaging device having a low aspect ratio, a simple structure, and capable of achieving lens characteristics corresponding to the main incident angle for each pixel.

[0011] Means for Solving the Problem

[0012] In order to solve the above problems and achieve the object, the imaging element of the present invention is characterized by having: a pixel array obtained by arranging a plurality of pixels each including a photoelectric conversion element in a two-dimensional array; and an optical element array disposed opposite to the pixel array and obtained by arranging optical elements in a two-dimensional array, the optical element being composed of a plurality of columnar structures that guide incident light to the corresponding photoelectric conversion element, and the plurality of columnar structures being formed in a width having the following phase characteristics when viewed from above, the phase characteristics being used to guide the incident light to the photoelectric conversion element directly below corresponding to the incident angle of the incident light on each columnar structure, and when viewed from the side, the plurality of columnar structures being formed to have the same height.

[0013] Furthermore, the imaging element according to the present invention is characterized by having: a pixel array obtained by arranging a plurality of pixels each including a photoelectric conversion element in a two-dimensional array; and an optical element array disposed opposite to the pixel array and obtained by arranging optical elements in a two-dimensional array, the optical element being composed of a plurality of columnar structures that guide incident light to the corresponding photoelectric conversion element, and the plurality of columnar structures having a refractive index having the following phase characteristics, the phase characteristics being used to guide the incident light to the photoelectric conversion element directly below corresponding to the incident angle of the incident light on each columnar structure, and when viewed from the side, the plurality of columnar structures being formed to have the same height.

[0014] Furthermore, the imaging device of the present invention is characterized by having: the imaging element described above; and a signal processing unit that processes the electrical signal output from the imaging element to generate an image.

[0015] Advantages of the Invention

[0016] According to the present invention, there can be provided an imaging element and an imaging apparatus including an optical element having a lower aspect ratio and a simpler structure than those in the related art and capable of achieving lens characteristics corresponding to a main incident angle for each pixel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. 1 is a side view schematically showing a schematic configuration of an imaging apparatus according to an embodiment.

[0018] Figure 2 FIG. 2 is a diagram schematically showing a part of a cross section of a pixel array and a polarization wavelength separation lens array of an imaging element according to an embodiment.

[0019] Figure 3 FIG. 3 is a diagram schematically showing a part of a cross section of a pixel array and an optical element array at a central portion of an imaging element according to an embodiment.

[0020] Figure 4 FIG. 4 is a diagram schematically showing a part of a cross section of a pixel array and an optical element array at an outer peripheral portion of an imaging element according to an embodiment.

[0021] Figure 5 FIG. 5 is a plan view of an optical element array at a central portion of an imaging element according to an embodiment.

[0022] Figure 6 FIG. 6 is a diagram showing a minimum structure height and a maximum aspect ratio of a dielectric approximation structure in the related art and a columnar structure in an embodiment.

[0023] Figure 7 FIG. 7 is a side view of a columnar structure.

[0024] Figure 8 FIG. 8 is a plan view of a columnar structure.

[0025] Figure 9 FIG. 9 is a diagram showing a relationship between a width of a columnar structure and a light transmittance.

[0026] Figure 10 FIG. 10 is a diagram showing a relationship between a width of a columnar structure and a phase characteristic of light of the columnar structure.

[0027] Figure 11 FIG. 11 is a diagram for explaining a definition of an incident angle.

[0028] Figure 12 FIG. 12 is a diagram showing a phase distribution as a design target of a lens and a lens pattern for realizing the phase distribution when light is incident at an incident angle of θ = 0° and φ = 0°.

[0029] Figure 13It is a diagram showing the phase distribution as the design target of the lens and the lens pattern for realizing the phase distribution when light is incident at an incident angle of θ = 45° and φ = 0°.

[0030] Figure 14 It is a diagram showing the phase distribution as the design target of the lens and the lens pattern for realizing the phase distribution when light is incident at an incident angle of θ = 45° and φ = 45°.

[0031] Figure 15 It is a diagram showing the condensing intensity of the optical element unit and its wavelength dependence.

[0032] Figure 16 It is a diagram showing the condensing intensity of the optical element unit and its wavelength dependence.

[0033] Figure 17 It is a diagram showing the condensing intensity of the optical element unit and its wavelength dependence.

[0034] Figure 18 It is a diagram showing the condensing intensity of the optical element unit when parallel light (λ = 520 nm) with φ = 0° is incident and the incident angle dependence of the incident light.

[0035] Figure 19 It is a diagram showing the condensing intensity of the optical element unit when parallel light (λ = 520 nm) with φ = 0° is incident and the incident angle dependence of the incident light.

[0036] Figure 20 It is a diagram showing the condensing intensity of the optical element unit when parallel light (λ = 520 nm) with φ = 0° is incident and the incident angle dependence of the incident light.

[0037] Figure 21 It is a diagram showing the condensing intensity of the optical element unit when parallel light (λ = 520 nm) with φ = 45° is incident and the incident angle dependence of the incident light.

[0038] Figure 22 It is a diagram showing the condensing intensity of the optical element unit when parallel light (λ = 520 nm) with φ = 45° is incident and the incident angle dependence of the incident light.

[0039] Figure 23 It is a diagram showing the condensing intensity of the optical element unit when parallel light (λ = 520 nm) with φ = 45° is incident and the incident angle dependence of the incident light.

[0040] Figure 24 It is a diagram schematically showing another example of a part of the cross-section of the pixel array and the optical element array in the imaging element of the embodiment. Detailed Embodiments

[0041] Hereinafter, the best mode for carrying out the present invention and the attached Figure 1 will be described in detail. In addition, in the following description, each figure schematically shows the shape, size, and positional relationship only to the extent that the content of the present invention can be understood. Therefore, the present invention is not limited only to the shape, size, and positional relationship illustrated in each figure. In addition, in the description of the drawings, the same reference numerals are given to the same parts.

[0042] [Embodiment]

[0043] [Imaging device]

[0044] First, the imaging device according to the embodiment of the present invention will be described. Figure 1 is a side view schematically showing the schematic structure of the imaging device according to the embodiment.

[0045] As Figure 1 shown, the imaging device 10 according to the embodiment includes a lens optical system 11, an imaging element 12, and a signal processing unit 13. The imaging element 12 has a photoelectric conversion element such as a CCD or a CMOS. The signal processing unit 13 processes the photoelectric conversion signal output from the imaging element 12 to generate an image signal.

[0046] Light such as natural light or illumination light is irradiated onto the object 1, and the light that passes through the object 1 or is reflected / scattered by the object 1, or the light emitted from the object 1 forms an optical image on the imaging element 12 through the lens optical system 11. Generally, in order to correct various optical aberrations, the lens optical system 11 is composed of a lens group, and the lens group is composed of a plurality of lenses arranged along the optical axis. However, Figure 1 a single lens is shown in the simplified drawing for simplicity. The signal processing unit 13 has an image signal output for sending the generated image signal to the outside.

[0047] In addition, the imaging device 10 may include known structural elements such as an optical filter for blocking infrared light, an electronic shutter, a viewfinder, a power source (battery), a flash, etc. However, their description is not particularly necessary for understanding the present invention, so it is omitted. In addition, the above structure is merely an example. In the embodiment, as structural elements other than the lens optical system 11, the imaging element 12, and the signal processing unit 13, known elements can be appropriately combined and used.

[0048] [Imaging element]

[0049] Next, the outline of the imaging element 12 according to the embodiment will be described. Figure 2 is a diagram schematically showing a cross-section of the main parts of the lens optical system 11 and the imaging element 12 according to the embodiment. In Figure 2Hereinafter, a part of the imaging element 12 will be described as the imaging element 100. The imaging element 100 has an optical element array, which is obtained by forming optical elements on the entire surface of a color filter. The optical elements are composed of a plurality of columnar structures that guide incident light to the photoelectric conversion elements of the pixel array. In addition, in the imaging element 100, as Figure 2 shown, since the incident angle θ of the light incident on the imaging element 100 from the lens optical system 11 is different between the central portion and the peripheral portion, the plurality of columnar structures formed in the optical element array are set to have a size that gives the following phase characteristics, which are used to guide the incident light to the photoelectric conversion element directly below corresponding to the incident angle of the incident light. Hereinafter, Figures 3 to 5 will be used to describe the structure of the imaging element 100.

[0050] Figure 3 FIG. is a diagram schematically showing a part of a cross section of a pixel array and an optical element array at the central portion of the imaging element according to the embodiment. Figure 4 FIG. is a diagram schematically showing a part of a cross section of a pixel array and an optical element array in the peripheral portion of the imaging element according to the embodiment. Figure 5 FIG. is a top view of the optical element array at the central portion of the imaging element according to the embodiment.

[0051] As Figure 3 and Figure 4 shown, the imaging element 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. In addition, the transparent layer 150 is a low-refractive-index transparent layer made of a material such as SiO2 (refractive index n = 1.45).

[0052] 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 G light, for example, and the pixels 130 of the pixel unit 140R receive R light.

[0053] The optical element array 120 is composed of optical elements arranged in a two-dimensional array, and the optical elements are composed of a plurality of columnar structures 160 that guide incident light to the photoelectric conversion elements of the corresponding pixels 130 directly below. For example, in Figure 5 it is shown that the wavelength regions separated by the color filter 170 are red (R), green (G), and blue (B). In Figure 5In the optical element array 120, optical element units 120R (optical elements) corresponding to R pixel units, two optical element units 120G (optical elements) corresponding to G pixel units, and optical element units 120B (optical elements) corresponding to B pixel units are formed as a set of optical element units on a two-dimensional array. Immediately below the optical element units 120R (optical elements) corresponding to R pixel units, the two optical element units 120G (optical elements) corresponding to G pixel units, and the optical element units 120B (optical elements) corresponding to B pixel units, R pixel units that receive R light, two G pixel units that receive G light, and B pixel units that receive B light on the pixel array 110 are arranged.

[0054] The plurality of columnar structures 160 are formed of a material having a refractive index higher than that of the surrounding materials (transparent layer 150, air). Thus, the columnar structures 160 strongly confine light inside the columnar structures and prevent optical coupling with adjacent columnar structures. The columnar structures 160 are formed, for example, using SiN (refractive index n = 2.05) and TiO2 (refractive index n = 2.4).

[0055] As Figure 3 and Figure 4 shown, the plurality of columnar structures 160 are formed to have the same height in a side view. The plurality of columnar structures 160 are formed at intervals shorter than the wavelength of the incident light over the entire surface of the optical element array 120. As Figure 5 shown, when looking down at the optical element units 120R, 120G, and 120B, the plurality of columnar structures 160 are formed in a lattice pattern. The plurality of columnar structures 160 are prisms. In addition, Figure 5 this example is just one example, and the columnar structures may also be structures with four-fold rotational symmetry such as a hollow square, a circle, a hollow circle, or a cross shape when looking down.

[0056] When looking down, the plurality of columnar structures 160 are formed to have a width w with the following phase characteristics, which are used to guide the incident light to the photoelectric conversion element of the corresponding pixel 130 directly below according to the incident angle of the incident light for each columnar structure. Each of the plurality of columnar structures 160 imparts an optical phase delay amount corresponding to the width of the columnar structure 160 when looking down to the incident light.

[0057] 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 gives a light phase delay amount distribution for guiding incident light to the respective photoelectric conversion elements of the corresponding R pixel unit, G pixel unit, and B pixel unit. In the optical element units 120R, 120G, and 120B, the width in a plan view of each of the plurality of columnar structures 160 forming the optical element units 120R, 120G, and 120B is set to a width that gives a light phase delay amount distribution for guiding the incident light to the photoelectric conversion element directly below the optical element units 120R, 120G, and 120B corresponding to the incident angle of the incident light. In addition, the light phase delay amount distribution is a light phase delay amount for converging light.

[0058] In the imaging element 100, a lens function is realized by forming columnar structures 160 having the same height and gradually changing widths over the entire surface of the optical element array 120. Since each columnar structure 160 acts like a columnar optical waveguide, in the imaging element 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.

[0059] In other words, each columnar structure 160 functions as a subwavelength-sized optical waveguide, and since light is confined and there is almost no optical coupling between adjacent columnar structures 160, by designing the width w in a plan view of the columnar structure 160 for each columnar structure 160, different optical characteristics (such as phase delay characteristics) can be given to each of the plurality of columnar structures 160. By making the spatial distribution of this phase delay amount the same as that of a (Fresnel) lens, a lens function can be given to the columnar structure 160.

[0060] Here, Non-Patent Document 1 describes that a structure made of a low refractive index material such as SiO2 functions as a lens.

[0061] Non-Patent Document 1 describes the following approximation: when the structure is very small compared to the wavelength, the effective refractive index of the structure can be expressed as approximately the average of the refractive indices of the structured lens and the surrounding material. However, when the difference in refractive index between the structure and the surrounding is large and the size of the structure is about subwavelength, light is confined inside the structure and excites an optical waveguide mode and a resonance mode, so this approximation cannot be applied. Therefore, the structures described in Non-Patent Document 1 are limited to combinations of materials with a small refractive index difference such as SiO2 for the material and air for the surrounding material, so the aspect ratio of the structure becomes large.

[0062] In contrast, in the imaging element 100, each columnar structure 160 is formed of a high refractive index material such as SiN or TiO2. Therefore, the height of the smallest columnar structure 160 required to achieve a phase change amount of 0 to 2π is lower than that of a structure made of a low refractive index material such as SiO2 (see Non-Patent Document 1). Therefore, the minimum structure height required for phase control of 0 to 2π in the imaging element 100 is relatively small, and the lens function can be realized with columnar structures 160 having an aspect ratio that is easy to fabricate.

[0063] Moreover, the plurality of columnar structures 160 are prisms having a square bottom surface. In this way, in the imaging element 100, by making each columnar structure 160 have a four-fold rotational symmetry structure such as a square in a top view, a characteristic independent of polarized light is achieved. It should be noted that it is obvious from the theoretical formula that the effective refractive index of the structure described in Non-Patent Document 1 has polarization dependence.

[0064] In addition, Non-Patent Document 1 describes a structure having a curved surface and steps. In contrast, each columnar structure 160 in the present embodiment is a prismatic binary pattern without a step difference. Therefore, the imaging element 100 can exclude the curved surface and steps from the cross section of the columnar structure, and thus the fabrication of the columnar structure 160 is easier than that of the structure described in Non-Patent Document 1.

[0065] In addition, in the imaging element 100, the lens function is realized by forming a plurality of columnar structures 160 on the entire surface of the optical element array 120. Therefore, all incident light can be received, and the lens aperture can be maximized.

[0066] In addition, each columnar structure 160 is formed to have a width w with the following phase characteristics in a top view, and this phase characteristic guides the incident light of each columnar structure 160 to the photoelectric conversion element of the pixel 130 directly below. That is, in the imaging element 100, according to the main incident angle, the structural pattern of the columnar structure 160 can be optimized for each pixel to improve the light reception efficiency. In other words, in the imaging element 100, according to the incident angle θ of the light incident on each columnar structure 160, the shape pattern of the columnar structure 160 in a top view is optimized.

[0067] As a result, in the imaging element 100, in either the outer peripheral portion where light is incident at a large incident angle θ (see Figure 4 ) or the central portion where light is incident perpendicularly (see Figure 3 ), the columnar structure 160 can condense light to the photoelectric conversion element of the pixel 130 directly below. Therefore, the imaging element 100 can converge more light to the photoelectric conversion element directly below and can generate an image signal having uniform brightness throughout the imaging element 100.

[0068] [Height of the columnar structure]

[0069] Next, the height when observing the columnar structure 160 from the side will be described. Hereinafter, the height when observing the columnar structure 160 from the side will be referred to as the height of the columnar structure 160. Moreover, the width when observing the columnar structure 160 from above 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 from 0 to 2π will be described.

[0070] If the wavelength of light in a vacuum is set to λ, the height of the columnar structure 160 is set to h, and the effective refractive index of the columnar structure 160 is set to n eff , and the refractive index of the surrounding material is set to n0, then the phase delay amount φ based on the columnar structure 160 is represented by Equation (1).

[0071] [Mathematical formula 1]

[0072]

[0073] Equation (1) is applicable both in the columnar structure 160 of the imaging element 100 and in the structure described in Non-Patent Document 1 (hereinafter referred to as the effective medium approximation structure).

[0074] It is known that in the case of the effective medium approximation structure, the effective refractive index n eff is determined by the area ratio of the structure to the surrounding material. In the case of the effective medium approximation structure, n eff also varies depending on the polarized light. Moreover, in the case of the columnar structure 160, the optical waveguide mode depends to a large extent on the width of the columnar structure 160, and thus it can be seen that the effective refractive index n eff is represented by 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, values of n0 < n eff < n1 are taken. In addition, n1 is the refractive index of the material constituting the structure.

[0075] Therefore, in order to control the phase change amount between 0 and 2π, the height of the structure needs to be set to Equation (2).

[0076] [Mathematical formula 2]

[0077] h ≥ λ0 / (n1 - n0)…(2)

[0078] Figure 6 is a diagram showing the minimum structural height and the maximum aspect ratio of the effective medium approximation structure in the prior art and the columnar structure 160 in the embodiment. In Figure 6In this case, when the wavelength of light is 635 nm, the minimum structure width is set to 100 nm, and the maximum aspect ratio is obtained.

[0079] To apply the effective medium approximation, it is necessary to reduce n1 - n0. Therefore, in the case of the effective medium approximation structure, the required height of the structure is as inevitably Figure 6 shown as high as 1411 nm, which is on the order of several wavelengths.

[0080] On the other hand, in the case of the columnar structure 160, from the viewpoint of confining light, it is preferable that n1 is larger, 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.

[0081] As a result, in the columnar structure 160, the required structural height is lower than that of the effective medium approximation structure, as Figure 6 shown, generally less than 1 wavelength. In this way, the aspect ratio of the columnar structure 160 is lower than that of the effective medium approximation structure.

[0082] [Structure of the columnar structure]

[0083] An example of the structure of the columnar structure 160 will be described. Figure 7 is a side view of the columnar structure 160. Figure 8 is a top view of the columnar structure 160. As Figure 7 and Figure 8 shown, for example, the columnar structure 160 is formed on the upper surface of the transparent layer 150u made of quartz. Moreover, the height (length in the z-axis direction) of the columnar structure 160 is set to h = 1000 nm, and the arrangement period of the columnar structure 160 is set to 320 nm. The width w of the columnar structure 160 is set corresponding to the phase of 0 to 2π to be controlled.

[0084] Figure 9 is a graph showing the relationship between the width w of the columnar structure 160 and the light transmittance. Figure 10 is a graph showing the relationship between the width w of the columnar structure 160 and the phase characteristics of the light of the columnar structure 160.

[0085] As Figure 9 shown, even when the width w of the columnar structure 160 is changed between 100 and 240 nm, a high transmittance can be maintained. Moreover, by adjusting the width w of the columnar structure 160 between 100 and 240 nm, the phase of the light transmitted through the columnar structure 160 can be controlled to a desired phase between 0 and 2π. In addition, in Figure 9 and Figure 10In this case, even when the width of the columnar structure 160 is reduced to 100 nm, the maximum value of the aspect ratio of the columnar structure 160 can be suppressed to 10.

[0086] [Lens Design]

[0087] In the imaging element 100 of the present embodiment, the phase distribution of the columnar structure 160 that functions as a lens is designed so as to condense light onto the center of the pixel 130 below the optical element array 120 corresponding to the incident angle. And in the imaging element 100, by referring to Figure 10 the phase characteristics of, the width w of each columnar structure 160 is set so as to achieve the designed phase distribution, thereby realizing the ideal phase distribution that is the design target.

[0088] For example, the parameters of a design example are shown below.

[0089] Size of one photoelectric conversion element = Area of lens: 3.2 μm × 3.2 μm

[0090] Focal length: 3.2 μm

[0091] Design wavelength: 520 nm

[0092] Figure 11 This is a diagram for explaining the definition of the incident angle. As Figure 11 shown, the case where light is incident at an incident angle of (θ, φ) is explained. For light with a certain incident angle (θ, φ), the phase distribution φ of the lens that converges the light to a point directly below the center of the lens (columnar structure 160) with a focal length f is represented by the following equation (3).

[0093] [Mathematical Equation 3]

[0094]

[0095] In Equation (3), λ d is the design wavelength, f is the focal length, n in is the refractive index of the material on the incident side, n out is the refractive index of the material on the exit side, and C is an arbitrary constant.

[0096] For example, f = 3.2 μm, n in = 1.0 (air), n out = 1.445 (quartz glass). φ is transformed so as to converge within the range of 0 to 2π. For example, when φ is -0.5π, it is converted to 1.5π, and when φ is 2.5π, it is converted to 0.5π. In this setting, referring to Figures 12 to 14The phase distribution that is the design objective of the lens when light is incident at an arbitrary incident angle, and the pattern of the lens (columnar structure 160) that can achieve this phase distribution. The phase distribution that is the design objective of the lens refers to the phase distribution of the lens that converges the light at a certain incident angle to a point directly below the center of the lens with a focal length f.

[0097] Figure 12 FIG. is a diagram showing the phase distribution that is the design objective of the lens when light is incident at an incident angle of θ = 0°, φ = 0°, and the pattern of the lens (columnar structure 160) that realizes this phase distribution. Figure 13 FIG. is a diagram showing the phase distribution that is the design objective of the lens when light is incident at an incident angle of θ = 45°, φ = 0°, and the lens pattern that realizes this phase distribution. Figure 14 FIG. is a diagram showing the phase distribution that is the design objective of the lens when light is incident at an incident angle of θ = 45°, φ = 45°, and the lens pattern that realizes this phase distribution. Figure 12 of (1), Figure 13 of (1), Figure 14 of (1) is the phase distribution that is the design objective of the lens when light is incident at the incident angles of each condition. Figure 12 of (2), Figure 13 of (2), Figure 14 of (2) can respectively realize Figure 12 of (1), Figure 13 of (1), Figure 14 of (1) is a top view of the columnar structure 160 that can realize the phase distribution, and is the shape pattern of the columnar structure 160 designed for one pixel.

[0098] As Figure 12 of (2), Figure 13 of (2), Figure 14 of (2) shows, the columnar structure 160 is a prism with a square bottom surface. Moreover, the width w of the columnar structure 160 is set to the following width based on Figure 10 the relationship between the width w of the columnar structure 160 shown and the phase characteristics of the light of the columnar structure 160, and this width can realize Figure 12 of (1), Figure 13 of (1), Figure 14 of (1) at each corresponding position in the phase distribution.

[0099] For example, Figure 12 the optical element unit 120-1 shown in of (2) is the shape pattern of the columnar structure 160 that realizes the phase distribution that is the design objective of the lens when light is incident at an incident angle of θ = 0°, φ = 0°. Figure 13The optical element unit 120-2 shown in (2) is a shape pattern of the columnar structure 160 that realizes the phase distribution that is the design target of the lens when light is incident at an incident angle of θ = 45° and φ = 0°. Figure 14 The optical element unit 120-3 shown in (2) is a shape pattern of the columnar structure 160 that realizes the phase distribution that is the design target of the lens when light is incident at an incident angle of θ = 45° and φ = 45°.

[0100] [Wavelength dependence of the condensing intensity]

[0101] In the embodiment, as Figure 5 shown in the optical element units 120R, 120G, and 120B, the patterns of the respective columnar structures 160 of the optical element units 120R, 120G, and 120B are designed corresponding to the design wavelengths of the photoelectric conversion elements of the pixel units directly below. In the optical element unit, the width w of each of the plurality of columnar structures 160 forming the optical element unit is set to the width that gives the following light phase delay amount distribution, which is used to guide the light in the 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. Therefore, the wavelength dependence of the condensing intensity of the optical element array 120 will be described.

[0102] Figures 15 to 17 is a graph showing the condensing intensity of the optical element unit and its wavelength dependence. Figure 15 Corresponding to B light with a wavelength of λ = 450 nm, Figure 16 Corresponding to G light with a wavelength of λ = 520 nm, Figure 17 Corresponding to R light with a wavelength of λ = 635 nm.

[0103] Figure 15 of (1), Figure 16 of (1), Figure 17 of (1) is a pattern of a lens (columnar structure 160) designed to be most suitable for vertically incident light (θ = 0°, φ = 0°), taking the average of two polarized lights. Figure 15 of (2), Figure 16 of (2), Figure 17 of (2) represents Figure 15 of (1), Figure 16 of (1), Figure 17 of (1) is a graph of the condensing intensity of the optical element units 120-4, 120-5, and 120-6. The condensing intensity is the total intensity within the converging spot width (λ / NA, where NA is the numerical aperture of the lens) on the photoelectric conversion element surface of the pixel 130. Figure 15 of (3),Figure 16 of (3), Figure 17 The (3) of Figure 17 is a graph showing the wavelength dependence of the light condensing intensity of the optical element units 120-4, 120-5, and 120-6.

[0104] As Figure 15 of (3), Figure 16 of (3), Figure 17 As shown by the (3) of Figure 17 , it can be seen that in the optical element units 120-4, 120-5, and 120-6, the light transmission structure is more than 96% and light can be received by the pixels 130. In addition, the light condensing intensity of the optical element units 120-4, 120-5, and 120-6 shows the maximum light condensing intensity around the design wavelength.

[0105] Therefore, in the imaging element 100, as long as the pattern of the columnar structure 160 is changed like the optical element units 120-4, 120-5, and 120-6 corresponding to each color band (transmission band of the color filters of R, G, B), it is possible to design light condensation that matches the design wavelength respectively. In the imaging element 100, the design wavelength of each pixel 130 is determined according to the color filter on the pixel 130, and the optical element units 120-4, 120-5, and 120-6 can be integrated respectively according to the design wavelength of the pixel 130 directly below.

[0106] [Design example of optical element unit corresponding to incident angle]

[0107] In the present 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 a plan view is set to a width that gives a light phase delay amount distribution for guiding the incident light to the photoelectric conversion element directly below the optical element unit corresponding 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 incident on the optical element array 120 will be described.

[0108] Figures 18 to 20 It is a graph showing the dependence of the light condensing intensity of the optical element unit on the incident angle of the incident light when parallel light (λ = 520 nm) with φ = 0° is incident. Figure 18 The (1) of Figure 18 is the pattern of the columnar structure 160 designed to be most suitable for the incident light with θ = 15° and φ = 0°, Figure 19 The (1) of Figure 19 is the pattern of the columnar structure 160 designed to be most suitable for the incident light with θ = 30° and φ = 0°, Figure 20 The (1) of Figure 20 is the pattern of the columnar structure 160 designed to be most suitable for the incident light with θ = 45° and φ = 0°, taking the average of two polarized lights. Figure 18(2) of Figure 19 (2) of Figure 20 (2) of represents Figure 18 (1) of Figure 19 (1) of Figure 20 (1) of the light condensing intensity diagrams of the optical element units 120-7, 120-8, and 120-9. Figure 18 (3) of Figure 19 (3) of Figure 20 (3) of represents the diagram of the incident angle dependence of the light condensing intensity of the optical element units 120-7, 120-8, and 120-9.

[0109] As Figure 18 (3) of Figure 19 (3) of Figure 20 (3) of As shown, in any one of the optical element units 120-7, 120-8, and 120-9, the maximum light condensing intensity is shown around the designed incident angle.

[0110] Figures 21 to 23 represents the diagram of the light condensing intensity of the optical element unit and the incident angle dependence of the incident light when parallel light (λ = 520nm) with φ = 45° is incident. Figure 21 (1) of is the pattern of the columnar structure 160 designed to be most suitable for the incident light with θ = 15° and φ = 45°. Figure 22 (1) of is the pattern of the columnar structure 160 designed to be most suitable for the incident light with θ = 30° and φ = 45°. Figure 23 (1) of is the pattern of the columnar structure 160 designed to be most suitable for the incident light with θ = 45° and φ = 45°, taking the average of two polarized lights. Figure 21 (2) of Figure 22 (2) of Figure 23 (2) of represents Figure 21 (1) of Figure 22 (1) of Figure 23 (1) of the light condensing intensity diagrams of the optical element units 120-10, 120-11, and 120-12. Figure 21 (3) of Figure 22 (3) of Figure 23 (3) of represents the diagram of the incident angle dependence of the light condensing intensity of the optical element units 120-10, 120-11, and 120-12.

[0111] As Figure 21 (3) of Figure 22 (3) of Figure 23 (3) of As shown, in any one of the optical element units 120-10, 120-11, and 120-12, the maximum light condensing intensity is shown around the designed incident angle.

[0112] In the imaging element 100, by arranging the above-described optical element units 120-7 to 120-12 corresponding to the incident angles (θ, φ) of incident light, it is possible to condense light with a relatively high intensity onto the photoelectric conversion element of the pixel 130 directly below.

[0113] [Effect of the Embodiment]

[0114] In this way, in the imaging element 100 of the embodiment, by forming a plurality of columnar structures 160 on the entire surface of the optical element array 120 at intervals shorter than the wavelength of the incident light to achieve the lens function, it is possible to receive all the incident light and improve the light reception efficiency.

[0115] In addition, in the imaging element 100, when viewed from above, the plurality of columnar structures are each formed to have a width with the following phase characteristics, which are used to guide the incident light corresponding to the incident angle of each columnar structure to the photoelectric conversion element directly below, and when viewed from the side, the plurality of columnar structures are formed to have the same height. In the imaging element 100, through the plurality of columnar structures 160, it is possible to achieve lens characteristics corresponding to the incident angle for each pixel 130, and thus it is possible to generate an image signal with uniform brightness in the entire imaging element 100.

[0116] In addition, in the imaging element 100, a plurality of columnar structures 160 of a quadrangular prism-shaped binary pattern made of a material having a refractive index higher than that of the surrounding material are used as lenses. Therefore, the plurality of columnar structures 160 used as lenses in the imaging element 100 have a lower aspect ratio and a simpler structure compared to the structure described in Non-Patent Document 1, and thus are easy to fabricate.

[0117] In addition, the optical element unit is not limited to the above structure, and various methods can be adopted for the number, interval, structural shape, and arrangement pattern. In addition, the columnar structures 160 can be either connected to each other or embedded in a transparent material.

[0118] In addition, in Figure 3 and Figure 4 the optical element array 120 is formed on the upper surface of the transparent layer 150, but it is not limited thereto. Figure 24 is a diagram showing another example of a part of the cross-section of the pixel array and the optical element array in the imaging element of the embodiment. As shown in the imaging element 100A of Figure 24 the optical element array 120A is formed on the bottom surface of an independent transparent substrate 190. In this way, the plurality of columnar structures 160 can also be formed inside the transparent layer 150A (for example, air).

[0119] In addition, in the above, an example where 4 pixels are located directly below one optical element unit has been described, but it is not limited thereto.

[0120] In addition, in the embodiment, an example in which SiN and TiO2 are used as the material of the columnar structure 160 has been shown, but it is not limited thereto. For example, when the imaging elements 100 and 100A are used in the visible light to near-infrared light region where the wavelength of light ranges from 380 nm to 1000 nm, materials such as SiN, SiC, TiO2, and GaN are applicable for the material of the columnar structure 160 because of their high refractive index and low absorption loss. In addition, when the imaging elements 100 and 100A are used in the near-infrared light region where the wavelength ranges from 800 to 1000 nm, materials such as Si, SiC, SiN, TiO2, GaAs, and GaN are applicable as the material of the columnar structure 160 with low loss for these lights. Moreover, in the near-infrared region of the long wavelength band (such as 1.3 μm and 1.55 μm which are communication wavelengths), in addition to the above materials, InP etc. can also be used as the material of the columnar structure 160.

[0121] Furthermore, in the case of forming a minute spectroscopic element such as the columnar structure 160 by attachment or coating, examples of the material include polymers such as polyimide such as fluorinated polyimide, BCB (benzocyclobutene), photocurable resin, UV epoxy resin, acrylic resin such as PMMA, and general resist.

[0122] Similarly, in the embodiment, an example in which SiO2 and an air layer are assumed as the materials of the transparent layers 150 and 150A has been shown, but it is not limited thereto. The materials of the transparent layers 150 and 150A only need to be general glass materials, SiO2, air layers, etc. whose refractive index is lower than that of the material of the columnar structure 160 and which have low loss with respect to the wavelength of incident light. In addition, the transparent layers 150 and 150A may also be transparent layers having a laminated structure composed of multiple materials.

[0123] In the embodiment, the case where the light in the wavelength band corresponding to the columnar structure 160 is light of the three primary colors R, G, and B has been described as an example, but at least one of the three bands may be light having a wavelength other than the three primary colors (for example, infrared light, ultraviolet light).

[0124] In addition, in the optical element arrays 120 and 120A, based on Figure 10The relationship between the width of the illustrated columnar structure 160 and the phase characteristics of light is such that the width of at least a part of the plurality of columnar structures 160 in a plan view is set to a width that gives a light phase delay amount distribution for guiding incident light to the corresponding photoelectric conversion element directly below. Thus, in the optical element arrays 120, 120A, lens characteristics corresponding to the incident angle and the wavelength range in the photoelectric conversion element are achieved for each pixel 130. Not limited to this, in the present embodiment, the plurality of columnar structures 160 may also have a refractive index having a phase characteristic for guiding the incident light corresponding to the incident angle of each columnar structure to the photoelectric conversion element directly below. In other words, in the present embodiment, it is also possible to achieve lens characteristics corresponding to the incident angle and the wavelength range in the photoelectric conversion element for each pixel 130 by setting the plurality of columnar structures 160 to have different refractive indices from each other. In addition, in the present embodiment, it is also possible to achieve lens characteristics corresponding to the incident angle and the wavelength range in the photoelectric conversion element for each pixel 130 by changing the width of the columnar structure 160 in a plan view and the refractive index of the columnar structure 160 for each columnar structure.

[0125] In addition, the optical element arrays 120, 120A in the present embodiment are, for example, metasurfaces. As described above, a metasurface is an element composed of a plurality of microstructures having a width below the wavelength of light, and may be a two-dimensional structure or a three-dimensional structure. By using a metasurface in an optical element, it is possible to control the phase and light intensity according to the characteristics of light (wavelength, polarization, incident angle) by changing the parameters of the microstructures. In addition, when the metasurface is a three-dimensional structure, the above-described design freedom is increased.

[0126] As described above, the present invention has been described based on specific embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist thereof.

[0127] Reference Numeral Explanation

[0128] 1 Object

[0129] 10 Imaging Device

[0130] 11 Lens Optical System

[0131] 12, 100, 100A Imaging Element

[0132] 13 Signal Processing Unit

[0133] 110 Pixel Array

[0134] 120, 120A Optical Element Array

[0135] 120R, 120G, 120B, 120-1 to 120-12 optical element units

[0136] 130 pixels

[0137] 140L, 140R pixel units

[0138] 150, 150A transparent layers

[0139] 160 columnar structures

[0140] 170 color filters

[0141] 180 wiring layers

[0142] 190 transparent substrates

Claims

1. An imaging element, characterized in that, comprising: a pixel array obtained by arranging a plurality of pixels each including a photoelectric conversion element in a two-dimensional array; and an optical element array disposed opposite to the pixel array and obtained by arranging optical elements in a two-dimensional array, the optical element being composed of a plurality of columnar structures that guide incident light to the corresponding photoelectric conversion element, the plurality of columnar structures are each formed in a width having the following phase characteristics in a plan view, the phase characteristics being used to guide the incident light to the photoelectric conversion element directly below corresponding to the incident angle of the incident light for each columnar structure, and in a side view, the plurality of columnar structures are formed to have the same height, the plurality of columnar structures each impart a light phase delay amount corresponding to the width of the columnar structure in a plan view to the incident light, in the optical element, the width of each of the plurality of columnar structures in a plan view is set to a width that imparts the following light phase delay amount distribution, the light phase delay amount distribution being used to guide the incident light to the photoelectric conversion element directly below the optical element corresponding to the design wavelength of the photoelectric conversion element directly below and the incident angle (θ, φ) of the incident light, where θ is the angle between the vertical axis, i.e., the z-axis, passing through the origin of the xy-plane of the optical element and the incident light when the plane of the optical element is set as the xy-plane and the incident light is incident on the origin of the xy-plane of the optical element, and φ is the angle between the projection of the incident light on the xy-plane of the optical element and the x-axis.

2. An imaging element, characterized in that, comprising: a pixel array obtained by arranging a plurality of pixels each including a photoelectric conversion element in a two-dimensional array; and an optical element array disposed opposite to the pixel array and obtained by arranging optical elements in a two-dimensional array, the optical element being composed of a plurality of columnar structures that guide incident light to the corresponding photoelectric conversion element, the plurality of columnar structures have the following refractive index having the following phase characteristics, the phase characteristics being used to guide the incident light to the photoelectric conversion element directly below corresponding to the incident angle of the incident light for each columnar structure, and in a side view, the plurality of columnar structures are formed to have the same height, the plurality of columnar structures each impart a light phase delay amount corresponding to the width of the columnar structure in a plan view to the incident light, in the optical element, the width of each of the plurality of columnar structures in a plan view is set to a width that imparts the following light phase delay amount distribution, the light phase delay amount distribution being used to guide the incident light to the photoelectric conversion element directly below the optical element corresponding to the design wavelength of the photoelectric conversion element directly below and the incident angle (θ, φ) of the incident light, where θ is the angle between the vertical axis, i.e., the z-axis, passing through the origin of the xy-plane of the optical element and the incident light when the plane of the optical element is set as the xy-plane and the incident light is incident on the origin of the xy-plane of the optical element, and φ is the angle between the projection of the incident light on the xy-plane of the optical element and the x-axis.

3. The imaging element according to claim 1 or 2, wherein the plurality of columnar structures are formed of a material having a refractive index higher than that of the surrounding material of the plurality of columnar structures, and are formed as the optical element array at intervals shorter than the wavelength of the incident light.

4. The imaging element according to claim 1 or 2, wherein the width of each of the plurality of columnar structures in a plan view is set to give a light phase delay amount distribution corresponding to the photoelectric conversion element directly below, and this light phase delay amount distribution is used to guide the incident light to the photoelectric conversion element directly below corresponding to the incident angle of the incident light.

5. The imaging element according to claim 1 or 2, wherein the width of each of the plurality of columnar structures in a plan view is set to different values according to the wavelength range of the photoelectric conversion element directly below.

6. The imaging element according to claim 1 or 2, wherein the light phase delay amount distribution is a light phase delay amount for converging light.

7. The imaging element according to any one of claims 1 to 2, wherein the plurality of columnar structures are prisms.

8. The imaging element according to any one of claims 1 to 2, wherein the imaging element further has a transparent layer formed on the pixel array, and the plurality of columnar structures are formed of a material having a refractive index higher than that of the transparent layer on the upper part or inside of the transparent layer.

9. The imaging element according to any one of claims 1 to 2, wherein the plurality of columnar structures have a four-fold rotational symmetry structure in a plan view.

10. An imaging device, characterized in that, Comprising: the imaging element according to any one of claims 1 to 9; and a signal processing unit that processes the electrical signal output by the imaging element and generates an image.

Images