Optical element, imaging element, and imaging device

Abstract

The imaging element (100) comprises: a transparent layer (150) for covering a plurality of pixels (130) each including a photoelectric conversion element; and a plurality of structures (160) arranged on the transparent layer (150) or in the transparent layer (150) in the surface direction of the transparent layer (150), wherein the plurality of structures (160) are arranged to converge a first light having a wavelength in the near-infrared region among incident light to a first pixel among the plurality of pixels (130), and to converge a second color light having a wavelength in a region outside the near-infrared region to a second pixel.

Description

Technical Field

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

[0002] A general 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 acquire a two-dimensional image consisting of intensity information and color information of light from an imaging object.

[0003] In recent years, there has been an increasing demand for capturing images of near-infrared (NIR) light in addition to visible light (color information). Near-infrared imaging devices are attracting attention for use in vehicle-mounted cameras, surveillance cameras, and the like because they can capture images at night.

[0004] Therefore, as an imaging element that captures both visible light color information and near-infrared images, in order to obtain color information and NIR information, a structure has been proposed in which four color filters of R (red), G (green), B (blue) and NIR are integrated on each pixel.

[0005] Prior art literature

[0006] Non-patent literature

[0007] Non-patent literature 1: Takanori Kudo, Yuki Nanjo, Yuko Nozaki, Kazuya Nagao, Hidemasa Yamaguchi, Wen-Bing Kang, Georg Pawlowski, "PIGMENTED PHOTORESISTS FORCOLOR FILTERS", Journal of Photopolymer Science and Technology, 1996, Volume 9, No. 1, p.109-119.

[0008] Non-patent literature 2: Monno, Yusuke, et al. "Single-Sensor RGB-NIR Imaging: High-Quality System Design and Prototype Implementation". IEEE Sensors Journal 19.2 (2018): 497-507. Summary of the invention

[0009] Problems to be solved by the invention

[0010] However, conventional imaging elements have the following problems: due to the absorption of light outside the transmission band by the color filter, the total amount of light received after passing through the filter is reduced, and the sensitivity is limited. In addition, a general color filter transmits part of the light in the NIR wavelength region, so in order to generate a color image in conventional imaging elements, color correction such as subtracting the NIR pixel value from the R, G, and B pixel values ​​is required.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical element, an imaging element, and an imaging device capable of improving the light receiving sensitivity of incident visible light and near-infrared light without causing light absorption.

[0012] Means for solving problems

[0013] In order to solve the above-mentioned problems and achieve the purpose, the optical element of the present invention is characterized in that it comprises: a transparent layer, which is used to cover multiple pixels respectively including photoelectric conversion elements; and multiple structures, which are arranged on the transparent layer or in the transparent layer in the surface direction of the transparent layer, and the multiple structures are arranged to converge the first light with a wavelength in the near-infrared light region in the incident light to the first pixel among the multiple pixels, and converge the second color light with a wavelength in the region outside the near-infrared light region to the second pixel.

[0014] In addition, the optical element of the present invention is characterized in that it comprises: a transparent layer, which is used to cover multiple pixels that respectively include photoelectric conversion elements; and multiple structures, which are arranged on the transparent layer or in the transparent layer in the surface direction of the transparent layer, and the multiple structures output a first light with a wavelength in the near-infrared light region among the incident light, and output a second color light with a wavelength in the region outside the near-infrared light region among the incident light.

[0015] Furthermore, the imaging element of the present invention is characterized by comprising the above-mentioned optical element and a plurality of pixels covered with a transparent layer.

[0016] Furthermore, the imaging device of the present invention is characterized by comprising the imaging element described above and a signal processing unit that generates an image signal based on an electrical signal obtained from the imaging element.

[0017] Effects of the Invention

[0018] According to the present invention, it is possible to improve the light receiving sensitivity of visible light of incident light without causing light absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a side view showing a schematic structure of the imaging device according to the first embodiment.

[0020] Figure 2 It is a diagram schematically showing the pixel arrangement of the pixel array when the imaging element is viewed from above.

[0021] Figure 3 It is shown along Figure 2 FIG. 1 is a diagram showing an example of a cross section of an imaging element when viewed from the side along line aa′ of FIG.

[0022] Figure 4 It is shown along Figure 2 FIG. 1 is a diagram showing an example of a cross section of an imaging element when viewed from the side along line bb'.

[0023] Figure 5 It is shown Figure 2 A plan view showing an example of the shape and arrangement of structures in the optical element array shown in the plan view.

[0024] Figure 6 FIG. 1 is a diagram schematically showing light focusing on pixels in an image sensor.

[0025] Figure 7 FIG. 1 is a diagram schematically showing light focusing on pixels in an image sensor.

[0026] Figure 8 FIG. 1 is a diagram schematically showing light focusing on pixels in an image sensor.

[0027] Fig. 9 FIG. 1 is a diagram schematically showing light focusing on pixels in an image sensor.

[0028] Fig.10 It is a diagram showing an example of a schematic structure of a structure.

[0029] Fig.11 It is a diagram showing an example of a schematic structure of a structure.

[0030] Fig.12 It is a diagram showing an example of a schematic structure of a structure.

[0031] Fig.13 It is a diagram showing an example of a schematic structure of a structure.

[0032] Fig.14 It is a diagram showing an example of a schematic structure of a structure.

[0033] Fig.15 It is a diagram showing an example of a schematic structure of a structure.

[0034] Fig.16 is a diagram schematically showing a pixel configuration of a pixel unit.

[0035] Fig.17This is a diagram showing an example of lens design when the structure is TiO2.

[0036] Fig.18 This is a diagram showing an example of lens design when the structure is TiO2.

[0037] Fig.19 This is a diagram showing an example of lens design when the structure is TiO2.

[0038] Fig. 20 This is a diagram showing an example of lens design when the structure is TiO2.

[0039] Fig.21 This is a diagram showing an example of lens design when the structure is TiO2.

[0040] Fig. 22 FIG. 1 is a diagram showing an example of the spectrum of light received by each pixel when the structural body is TiO 2 .

[0041] Fig.23 This 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 image sensor according to the first embodiment.

[0042] Fig.24 This 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 image sensor according to the first embodiment.

[0043] Fig.25 It is a figure which shows the example of the cross-sectional shape of a structure.

[0044] Fig.26 This is a diagram showing an example of a schematic configuration of an image pickup element according to the second embodiment.

[0045] Fig. 27 This is a diagram showing an example of a schematic configuration of an image pickup element according to the second embodiment.

[0046] Fig.28 It is shown Fig.26 and Fig. 27 FIG. 1 is a diagram showing an example of a spectrum of light received by each pixel of the imaging element shown.

[0047] Fig.29 This is a diagram showing an example of a schematic configuration of an image pickup element according to a modified example of the second embodiment.

[0048] Fig.30 This is a diagram showing an example of a schematic configuration of an image pickup element according to a modified example of the second embodiment.

[0049] Fig.31 This is a diagram showing an example of a schematic configuration of an image pickup element according to a modified example of the second embodiment.

[0050] Fig.32 This is a diagram showing an example of a schematic configuration of an image pickup element according to a modified example of the second embodiment. DETAILED DESCRIPTION

[0051] Hereinafter, the best mode for implementing the present invention will be described in detail with reference to the accompanying drawings. In addition, in the following description, each figure only schematically shows the shape, size and positional relationship to the extent that the content of the present invention can be understood, and therefore, the present invention is not limited to the shape, size and positional relationship illustrated in each figure. In addition, in the description of the accompanying drawings, the same reference numerals are used to indicate the same parts.

[0052] [Implementation Method 1]

[0053] [Camera device]

[0054] First, an imaging device according to Embodiment 1 of the present invention will be described. Figure 1 This is a side view showing a schematic structure of the imaging device according to the first embodiment.

[0055] like Figure 1 As shown, the imaging device 10 of the first embodiment includes a lens optical system 11, an imaging element 12, and a signal processing unit 13. The lens optical system 11 includes 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.

[0056] The object 1 is irradiated with light such as natural light or illumination light, and the light transmitted / 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. Figure 1 The lens optical system 11 is shown as a single lens in the simplified drawing. The signal processing unit 13 has an image signal output for sending the generated image signal to the outside.

[0057] In addition, the imaging device 10 may include known components such as an optical filter that cuts off infrared light, an electronic shutter, a viewfinder, a power source (battery), and a flash, but their description is not particularly necessary for understanding the present invention and is therefore omitted. In addition, the above structure is only an example, and in Embodiment 1, as components other than the lens optical system 11, the imaging element 12, and the signal processing unit 13, known components can be appropriately combined and used.

[0058] [Image sensor]

[0059] Next, the image pickup element 12 of the first embodiment is described in outline. The image pickup element 12 of the first embodiment includes: a pixel array in which a plurality of pixels including a photoelectric conversion element are arranged in a two-dimensional array; and an optical element array (optical element) on the entire surface of which a plurality of fine structures are arranged, and the plurality of fine structures have a wavelength separation function and a light focusing function for focusing light on each pixel. In addition, a part of the image pickup element 12 is described below as the image pickup element 100.

[0060] Figure 2 It is a diagram schematically showing the pixel arrangement of the pixel array when the imaging element is viewed from above. Figure 3 It is shown along Figure 2 FIG. 1 is a diagram showing an example of a cross section of the image sensor 100 when viewed from the side along line aa′. Figure 4 It is shown along Figure 2 FIG. 1 is a diagram showing an example of a cross section of the imaging element 100 when viewed from the side along the line bb′. Figure 3 and Figure 4 In FIG. 1 , arrows schematically indicate light incident on the imaging element 100 . Figure 5 It is shown Figure 2 A top view of an example of the shape and configuration of a structure in the optical element array shown in the top view. The xyz coordinate system is shown in the figure. The xy plane direction corresponds to the surface direction of the pixel array 110, transparent layer 150, etc. described later. In the following, unless otherwise specified, "top view" refers to observation in the z-axis direction (for example, the negative direction of the z-axis). "Side view" refers to observation in the x-axis direction or the y-axis direction (for example, the negative direction of the y-axis).

[0061] like Figure 3 and Figure 4 As shown, the image sensor 100 includes a pixel array 110 and an optical element array 120 disposed opposite to the pixel array 110. The pixel array 110 and the optical element array 120 are arranged in sequence in the positive z-axis direction.

[0062] like Figure 2 to Figure 4 As shown, 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 the transparent layer 150, and the transparent layer 150 is formed on the pixel array 110. In addition, the transparent layer 150 is a low refractive index transparent layer composed of a material such as SiO2 (refractive index n=1.45).

[0063] The pixel array 110 includes a wiring layer 180 and a plurality of pixels 130 arranged in the xy plane direction. Each pixel 130 is constituted by including a photoelectric conversion element. An example of a photoelectric conversion element is a photodiode (PD). Each pixel corresponds to red (R), green (G), blue (B), and near infrared (NIR). As an example of a wavelength band of red light, if the wavelength is set to λ0, 600nm<λ0≤800nm. An example of a wavelength band of green light is 500nm<λ0≤600nm. An example of a wavelength band of blue light is λ0≤500nm. An example of a wavelength band of near infrared light is 800~1000nm. In order to distinguish each pixel, it is illustrated as pixel R, pixel G, pixel B, and pixel NIR. As shown Figure 2 As shown, four pixels R, G, B and NIR are arranged in a Bayer arrangement to form a pixel unit U1.

[0064] The incident light travels along the negative direction of the z-axis and reaches the pixel array 110 via the optical element array 120. The optical element array 120 focuses the red light in the incident light onto the pixel R, the green light onto the pixel G, the blue light onto the pixel B, and the near infrared light onto the pixel NIR. The charges generated in the pixel R, the pixel G, the pixel B, and the pixel NIR are converted into an electrical signal as the basis of the pixel signal by a transistor (not shown) and the like, and are output to the outside of the imaging element 100 via the wiring layer 180. Figure 3 and Figure 4 , some of the wirings included in wiring layer 180 are shown.

[0065] The optical element array 120 is arranged in a manner covering the pixel array 110. An example of the optical element array 120 is a meta-surface. The meta-surface is composed of a plurality of microstructures (equivalent to the structure 160) having a width less than the wavelength of light. The meta-surface can have a two-dimensional structure or a three-dimensional structure. For the optical element array 120, the phase and light intensity can be controlled according to the characteristics of the light (wavelength, polarization, incident angle) simply by changing the parameters of the structure 160. In the case of a three-dimensional structure, the design freedom is improved compared to a two-dimensional structure.

[0066] The optical element array 120 has two functions, namely, a wavelength separation function and a lens function. The wavelength separation function is a function of separating the incident light into light of each wavelength band. The lens function is a function of converging light of each wavelength to the corresponding pixel. In this example, the incident light is separated into red light, green light, blue light and NIR light by the wavelength separation function of the optical element array 120. By the lens function, the red light is converged to the pixel R, the green light is converged to the pixel G, the blue light is converged to the pixel B, and the NIR light is converged to the pixel NIR.

[0067] The optical element array 120 includes a transparent layer 150 and a plurality of structures 160. The transparent layer 150 is disposed on the pixel array 110 in a manner covering the pixel array 110. The transparent layer 150 has a refractive index lower than that of the structures 160. Examples of the material of the transparent layer 150 are SiO2 and the like. The transparent layer 150 may be a void, in which case the refractive index of the transparent layer 150 may be equal to the refractive index of air. The material of the transparent layer 150 may be a single material or a material in which a plurality of materials are layered.

[0068] A plurality of structures 160 are arranged on or in the transparent layer 150, for example, periodically (having a periodic structure) in the surface direction (xy plane direction) of the transparent layer 150. In this example, the structure 160 is arranged on the transparent layer 150 on the side opposite to the pixel array 110 (the positive z-axis direction side) across the transparent layer 150. In order to make the design easier, etc., the plurality of structures 160 can be arranged at equal intervals or at unequal intervals. Each structure 160 is a microstructure having a nanometer-scale size that is the same as or smaller than the wavelength of the incident light. The plurality of structures 160 have the same height when viewed from the side.

[0069] Figure 5 Schematically shows the Figure 2 An example of the shapes and configurations of multiple structures 160 in the area corresponding to the pixel unit U1 when viewed from above. The structure 160 has, for example, a square shape, a cross shape, or a circular shape when viewed from above. The basic shapes of the square, cross, and circular structures 160 are the same and have different sizes (length, width, etc.). The shape of the structure 160 when viewed from above can be a four-fold rotationally symmetrical shape. Such a shape can be composed of, for example, at least one of a square shape, a cross shape, and a circular shape. By making each structure 160 a four-fold rotationally symmetrical shape when viewed from above, it has characteristics that are independent of polarization.

[0070] exist Figure 5 In the example of FIG. 1 , an X-shape and a hollow rhombus shape obtained by rotating a square shape and a cross shape by 45° in a plane are shown as the shape of the structure 160 when viewed from above. In addition, the hollow rhombus shape is an example of a shape including a square shape, and is a shape obtained by rotating a hollow square shape by 45° in a plane.

[0071] In addition, if a shape such as an X-shape or a rhombus is used, which is obtained by rotating the surface by 45 degrees, the optical coupling with the adjacent structures becomes weaker, so the optical characteristics of each structure are not affected by the adjacent structures and are easily maintained. As a result, it is easy to reproduce the ideal phase delay amount distribution described later.

[0072] Figure 6 to Figure 9 Schematically shows the focusing of light onto pixels in the image sensor 100. Figure 6 As shown by the arrow in the middle, the blue light converges to the pixel B. In this example, not only the light above the pixel B (in the positive direction of the Z axis), but also the light above the pixels around the pixel B converges to the pixel B. That is, the plurality of structures 160 ( Figure 3 to Figure 5 ) is configured so that light of a color corresponding to pixel B among light incident on the outside of the area opposite to pixel B is also focused on pixel B. Thus, compared with a case where only light incident on the area opposite to pixel B is focused on pixel B, the amount of received light can be increased.

[0073] In the imaging element 100, as shown in FIG. Figure 7 As shown by the arrow in the figure, green light is focused on the pixel G. In this example, not only the light above the pixel G, but also the light above the pixels around the pixel G is focused on the pixel G. That is, the plurality of structures 160 are arranged so that the light of the color corresponding to the pixel G among the light incident on the outside of the region corresponding to the pixel G is also focused on the pixel G. Thus, compared with the case where only the light incident on the region corresponding to the pixel G is focused on the pixel G, the amount of received light can be increased.

[0074] In the imaging element 100, as shown in FIG. Figure 8 As shown by the middle arrow, the red light is focused on the pixel R. In this example, not only the light above the pixel R, but also the light above the pixels around the pixel R is focused on the pixel R. That is, the plurality of structures 160 are arranged so that the light of the color corresponding to the pixel R among the light incident on the outside of the region opposing the pixel R is also focused on the pixel R. Thus, compared with the case where only the light incident on the region opposing the pixel R is focused on the pixel R, the amount of received light can be increased.

[0075] In the imaging element 100, as shown in FIG. Fig. 9 As shown by the middle arrow, near infrared light converges to the pixel NIR. In this example, not only the light above the pixel NIR, but also the light above the pixels around the pixel NIR converges to the pixel NIR. That is, the plurality of structures 160 are configured so that the light of the color corresponding to the pixel NIR among the light incident on the outside of the area opposite to the pixel NIR is also converged to the pixel NIR. Thus, compared with the case where only the light incident on the area opposite to the pixel NIR is converged to the pixel NIR, the amount of received light can be increased.

[0076] In this way, the plurality of structures 160 converges red light, green light, blue light, and NIR light into the pixel R, the pixel G, and the pixel B, among incident light.

[0077] [Structure]

[0078] In order to realize the structure 160 having different focusing positions according to the wavelength region of the incident light, it is necessary to realize a structure that gives different light wavefronts to each wavelength region. In the first embodiment, by utilizing the wavelength dispersion characteristics of the phase delay amount given to the incident light by the fine columnar structure 160, both the wavelength separation function and the focusing function are realized.

[0079] The structure 160 is formed of a material such as TiO2 or SiN having a refractive index n1 higher than the refractive index n0 of the transparent layer 150 or air surrounding the structure, and the height (length in the z-axis direction) h of the structure 160 when viewed from the side is constant. The structure 160 can be considered as an optical waveguide that confines light within the structure and propagates it based on the difference in refractive index with the transparent layer.

[0080] Therefore, when light enters from the lens optical system 11 side, the light propagates while being firmly confined in the structure and is affected by the effective refractive index n of the optical waveguide. eff The determined phase delay effect is output from the pixel array 110 side.

[0081] Specifically, when the phase of light propagating in the transparent layer by a length corresponding to the thickness of the structure is used as a reference, if the wavelength of the light in a vacuum is λ, the phase delay amount based on the structure 160 is It is expressed by formula (1).

[0082] [Mathematical formula 1]

[0083]

[0084] The phase delay Since it differs according to the wavelength λ of light, in the same structure, it is possible to provide different phase delay amounts to light according to the wavelength region.

[0085] In addition, the effective refractive index n of the optical waveguide is known to be eff It depends largely on the cross-sectional shape of the structure 160, and n0<n eff <n1 value. In addition, the effective refractive index n of the optical waveguide eff The wavelength λ of the light varies, and the degree thereof largely depends on the cross-sectional shape of the structure 160 .

[0086] Therefore, by using the columnar structure 160 having various cross-sectional shapes, various combinations of phase delay amounts corresponding to the wavelength λ of light can be set, and a lens having different focusing positions according to wavelength regions can be newly designed and realized.

[0087] [Shape of the structure]

[0088] Figure 10 to Figure 15 1 is a diagram showing an example of a schematic structure of the structure 160 . Fig.10 It is a side view of the structure 160 which has a square shape when viewed from above. Fig.11 yes Fig.10 A top view of structure 160 is shown. Fig.12 It is a side view of the structure 160 which has an X-shape when viewed from above. Fig.13 yes Fig.12 A top view of structure 160 is shown. Fig.14 It is a side view of the structure 160 having a hollow rhombus shape when viewed from above. Fig.15 yes Fig.14 A top view of structure 160 is shown.

[0089] The structure 160 is a columnar structure extending in the z-axis direction and is formed on the transparent layer 150 (e.g., SiO2 substrate (refractive index 1.45)). An example of the material of the structure 160 is TiO2 (refractive index 2.40). The side and top of the structure 160 are air (Air (refractive index 1.0)).

[0090] The arrangement period of each structure 160 is denoted by P. The arrangement period P is preferably set as shown in Formula (2) so that no diffracted light is generated on the transmission side.

[0091] [Mathematical formula 2]

[0092] P≤λ min / n2 …(2)

[0093] λ min is the shortest wavelength in the wavelength band of the light receiving object, for example, 410 nm. n2 is the refractive index of the transparent layer 150, and when the transparent layer 150 is SiO2, n2 = 1.45. The arrangement period P of the structure 160 is, for example, 280 nm.

[0094] exist Figure 10 to Figure 15 In the figure, the height of the structure 160 when viewed from the side (the length in the z-axis direction) is referred to as the height h. The height h of the structure 160 is constant. The height h is preferably set as in formula (3) so that the structure 160 can impart an optical phase delay (phase value) of 2π or more to the incident light, i.e., the light traveling along the z-axis direction.

[0095] [Mathematical formula 3]

[0096] h≥λ r (n1-n0) …(3)

[0097] Wavelength r It is the desired central wavelength in the wavelength band of the light to be separated as the object of wavelength separation. n1 is the refractive index of the structure 160. In the case where the structure 160 is TiO2, n1=2.40, and the height h is, for example, 1250nm. In addition, the structure 160 can also be formed of SiN (refractive index 2.05). In this case, n1=2.05, and the height h of the structure 160 is, for example, 1600nm.

[0098] Various combinations that can provide different optical phase delays to light of different wavelengths can be realized by designing the cross-sectional shape (including dimensional design) of the structure 160. By diversifying the cross-sectional shape of the structure 160, the combinations increase, and the degree of design freedom is further improved.

[0099] [Example of lens design]

[0100] Reference Figure 16 to Figure 21 An example of lens design will be described. Fig.16 1 is a diagram schematically showing the pixel configuration of a pixel unit. In lens design, the cross-sectional shape and configuration of the structure 160 are designed so as to achieve an ideal light phase delay amount distribution (phase distribution). In the example described below, the cross-sectional shape and configuration of the structure 160 composed of the TiO2 structure are designed according to the ideal light phase delay amount distribution of the center wavelength of each wavelength band of red light, green light, blue light and near infrared light, so that the red light, green light, blue light and near infrared light are respectively focused on Fig.16 The pixels shown are R, G, B, and NIR. For example, the pixel size is 1.68 μm × 1.68 μm. The focal length is 5.0 μm. The central wavelength corresponding to blue light is 430 nm. The central wavelength corresponding to green light is 520 nm. The central wavelength corresponding to red light is 635 nm. The central wavelength corresponding to near infrared light is 850 nm.

[0101] If the ideal optical phase delay distribution is set to but It is represented by the following formula (4).

[0102] [Formula 4]

[0103]

[0104] In the above formula (4), λ d is the center wavelength (design wavelength).f ,y f and z f is the focusing position. n2 is the refractive index of the underlying transparent layer 150. C is an arbitrary constant.

[0105] The ideal optical phase retardation distribution is a phase distribution that gives the following light-collecting positions to each of the pixels B, G, R, and NIR: The center positions of the four pixels (pixel units) correspond to x=0 and y=0.

[0106] Pixel B: x f = +0.84 μm, y f =-0.84 μm, z f =5.0μm

[0107] Pixel G:x f = +0.84 μm, y f = +0.84 μm, z f =5.0μm

[0108] Pixel R: x f =-0.84μm, y f = +0.84 μm, z f =5.0μm

[0109] Pixel NIR: x f =-0.84μm, y f =-0.84 μm, z f =5.0μm

[0110] It is transformed in a manner that converges to the range of 0 to 2π. For example, -0.5π and 2.5π are transformed into 1.5π and 0.5π, respectively. The boundary area of ​​the optical phase delay distribution is set so that the optical phase delay distribution at each center wavelength is symmetrical left and right and up and down with the focusing position as the center (together with the adjacent lens). The constant C can be optimized so that the error (difference from the ideal value) of the optical phase delay distribution at each wavelength is minimized. According to the optical phase delay at each wavelength, the structure that is most suitable for the optical phase delay distribution at each center wavelength of the above-mentioned four wavelengths (the structure with the smallest error) is arranged at the corresponding position.

[0111] Figures 17 to 21 FIG. 1 is a diagram showing an example of lens design when the structure 160 is TiO 2 . Fig.21 1 is a top view showing an example of the shape and arrangement of the structure 160 when viewed from above. Fig.21 As shown, according to Fig.16The plurality of structures 160 are formed by the shapes and arrangements in which the light of wavelengths corresponding to the pixels R, G, B, and NIR are converged. Fig.21 The center position of corresponds to x=0, y=0.

[0112] Fig.17 The ideal optical phase retardation distribution (Phase (rad / π)) when the central wavelength is 430 nm (blue light) is shown. Fig.18 An ideal optical phase delay distribution when the central wavelength is 520 nm (green light) is shown. Fig.19 An ideal optical phase delay distribution when the central wavelength is 635 nm (red light) is shown. Fig. 20 An ideal optical phase retardation distribution when the central wavelength is 850 nm (near infrared light) is shown.

[0113] Fig.21 is achievable Figures 17 to 20 The top view of the structure 160 of the respective optical phase delay distribution is for each pixel unit (refer to Fig.16 ) The shape pattern of the structure 160 designed. Fig.21 As shown, the shape of the structure 160 is a square shape, an X shape, or a hollow rhombus prism. The planar shape of the structure 160 is set to achieve Figures 17 to 20 The shape of the phase of the corresponding position in the light phase delay amount distribution shown. Therefore, the planar shape of the structure 160 may not be a square shape, an X shape, a hollow rhombus, or a plurality of shapes, but may be set to one shape (for example, a square shape). In addition, the shape of the structure 160 can be set to any shape of a square shape, an X shape, or a hollow rhombus, and is not limited to the wavelength region of the separation object. In addition, the type of the planar shape of the structure 160 may also be set for each wavelength region of the separation object.

[0114] Fig. 22 : is a diagram showing an example of the spectrum of light received by each pixel when the structure 160 is TiO2. The spectrum is the spectrum when an unpolarized plane light wave is incident perpendicularly to the substrate (xy plane). The distance from the lower end of the structure 160 (lens structure end) to the pixel array 110 is 5.0μm (lens focal length). The horizontal axis of the graph represents the wavelength (Wavelength (nm)). The vertical axis represents the light receiving efficiency (Detected power). The light receiving efficiency is (light intensity on 1 pixel) / (incident light intensity incident on the structure 160 (lens (area of ​​4 pixels))). For example, when half of the light incident on the structure 160 is incident on the pixel, the light receiving efficiency is 0.5.

[0115] Light is focused on each pixel in such a way that each pixel has a peak in the corresponding light band. The spectrum of light incident on pixel R is represented by curve R. The spectrum of light incident on pixel G is represented by curve G. The spectrum of light incident on pixel B is represented by curve B. The spectrum of light incident on pixel NIR is represented by curve NIR. As a comparative example, the upper limit value of the light receiving efficiency of 0.2 in the case where a general filter (color filter) is used instead of the optical element array 120 of embodiment 1 is represented as the filter limit (Filter limit (T max =80%)). The upper limit value of the light receiving efficiency, 0.2, is a value obtained by dividing the filter having a maximum transmittance of 80% at each wavelength into four pixels, namely, pixel R, pixel G, pixel B, and pixel NIR (0.8 / 4=0.2).

[0116] It can be seen that pixel R, pixel G, pixel B and pixel NIR all have peak values ​​greater than the upper limit value of 0.2 of the comparative example, and the amount of light received in the pixel is greater than that of the comparative example. For example, at a wavelength of 430nm, the light receiving efficiency of pixel B greatly exceeds the upper limit value of 0.2 of the comparative example. At a wavelength of 525nm, the light receiving efficiency of pixel G also greatly exceeds the upper limit value of 0.2 of the comparative example. At a wavelength of 635nm, the light receiving efficiency of pixel R also greatly exceeds the upper limit value of 0.2 of the comparative example. At a wavelength of 850nm, the light receiving efficiency of pixel NIR also greatly exceeds the upper limit value of 0.2 of the comparative example.

[0117] The total transmittance of the lens, i.e., (the sum of the light intensities on all pixels) / (the incident light intensity incident on the structure 160), is averaged within the wavelength range of 400nm to 900nm, and the value is 94.7%, which is capable of receiving almost all incident light, greatly exceeding the upper limit of 30% when using a general filter. It can also be seen from this that the light receiving efficiency can be improved in any of the pixels R, G, B, and NIR, and it can be confirmed that the amount of light received has increased.

[0118] [Effects of Embodiment 1]

[0119] As described above, according to the optical element array 120, two functions, namely, the wavelength separation function and the lens function for red light, green light, blue light, and near-infrared light, are realized. For example, the imaging element of the prior art does not have the optical element array 120, but has an optical filter (e.g., a color filter). That is, for example, in the imaging element of the prior art, the optical filter corresponding to the color of each pixel is set in a manner covering the pixel. In this case, for example, in the imaging element of the prior art, since the light of wavelengths outside the transmission band is absorbed by the optical filter, the amount of light passing through the optical filter only remains about 1 / 4 of the amount of light incident on the optical filter, and the light receiving efficiency is reduced.

[0120] In contrast, according to the imaging element 100 of Embodiment 1, as described above, the light receiving amount is maintained to be greater than that (for example, greater than 90%), so the light receiving efficiency is greatly improved. In addition, the imaging element 100 of this embodiment may not be provided with a filter, so the color correction processing required for generating a color image by a conventional imaging element is not required, and the color reproducibility can be improved.

[0121] In addition, in the prior art, in order to increase the amount of received light (increase sensitivity) by increasing the aperture ratio and reducing the light incident angle dependency, there is also a technology of providing (integrating) a microlens on the side opposite to the pixel across the filter. In this case, since it becomes a two-layer structure with at least a filter and a microlens, the structure becomes complicated and the manufacturing cost also increases.

[0122] In contrast, according to the optical element array 120 of embodiment 1, the wavelength separation function and the lens function can be realized only by the optical element array 120, so the structure can be simplified and the manufacturing cost can be reduced. In addition, a plurality of structures 160 can be arranged without gaps in the plane (in the xy plane), so the aperture ratio is increased compared to the microlens.

[0123] in addition, Figure 1 The signal processing unit 13 shown generates a pixel signal based on the electrical signal obtained from the imaging element 12. In order to obtain the electrical signal, the signal processing unit 13 also controls the imaging element 12. The control of the imaging element 12 includes: exposing the pixels of the imaging element 12, converting the charges accumulated in the pixel array 110 into electrical signals, reading out the electrical signals, etc.

[0124] In addition, the optical element array 120 is not limited to the above-mentioned structure, and various methods can be adopted for the number, interval, structure shape, and arrangement pattern of the structures 160. In addition, the structures 160 may be connected to each other or may be buried in a transparent material.

[0125] In addition, Figure 3 and Figure 4 In the embodiment, the optical element array 120 is formed on the upper surface of the transparent layer 150, but is not limited thereto. Fig.23 and Fig.24 This 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 image sensor according to the first embodiment.

[0126] like Fig.23 As shown in the imaging element 100A of FIG. 1 , the optical element array 120 may be buried inside the transparent layer 150A on the pixel 130. In this case, the material of the transparent layer 150A may be a single material or a material formed of multiple materials in a layered form. Fig.24As shown in the imaging element 100B, the optical element array 120 may also be formed on the bottom surface of an independent transparent substrate 190. In this case, the area between the optical element array 120 and the pixel 130 is filled with air 150B. In this case, the material of the transparent substrate 190 may be a single material or a material in which multiple materials are layered. The imaging elements 100, 100A, and 100B may also be used together with on-chip microlenses, internal microlenses, and pixel barriers for reducing crosstalk.

[0127] In the above description, an example in which four pixels are located directly under one optical element unit is described, but the present invention is not limited to this.

[0128] In addition, the cross-sectional shape of the structure 160 is not limited to the previously described Figure 5 The shapes shown. Fig.25 is a diagram showing an example of a cross-sectional shape of a structure. The structure 160 may have Fig.25 Various cross-sectional shapes shown as examples. The shapes shown as examples are four-fold rotationally symmetrical shapes obtained by variously combining a square shape, a cross shape, and a circle shape.

[0129] [Implementation Method 2]

[0130] In Embodiment 2, a configuration in which an image pickup element includes an optical filter is described. Fig.26 and Fig. 27 This is a diagram showing an example of a schematic configuration of an image pickup element according to the second embodiment.

[0131] Fig.26 and Fig. 27 The illustrated imaging element 200 has a filter layer 170 disposed between the pixel array 110 and the optical element array 120 . Fig.26 Shows the Figure 2 An example of a cross section of the imaging element 200 when viewed from the side along the line aa′ when the imaging element 100 in FIG. 1 is replaced by the imaging element 200 . Fig. 27 Shows the Figure 2 An example of a cross section of the imaging element 200 when viewed from the side along line bb′ when the imaging element 100 in FIG. 1 is replaced by the imaging element 200 .

[0132] The filter layer 170 includes a filter 170R, which is provided in a manner covering the pixel R and allows red light to pass through; a filter 170G, which is provided in a manner covering the pixel G and allows green light to pass through; a filter 170B, which is provided in a manner covering the pixel B and allows blue light to pass through; and a filter 170NIR, which is provided in a manner covering the pixel NIR and allows near infrared light to pass through. Examples of the material of the filter layer 170 are organic materials such as resin.

[0133] The light that has been color-separated by the optical element array 120 further passes through the filter layer 170 and reaches the pixel array 110. By performing wavelength separation by both the optical element array 120 and the filter layer 170, the crosstalk of the spectrum is suppressed (most of the unnecessary other wavelength components are removed) compared to the case where only one side performs wavelength separation, and the color reproducibility is improved. In addition, since the incident light passes through the filter layer 170 after being separated by the optical element array 120, the amount of light is not greatly reduced. Therefore, compared with the case where there is no optical element array 120 and only the filter layer 170 is provided, the light receiving efficiency of the pixel is improved.

[0134] Fig.28 It is shown Fig.26 and Fig. 27 FIG. 2 is a diagram showing an example of a spectrum of light received by each pixel of the imaging element 200 shown. Fig.28 An example of a spectrum when the structure 160 is TiO 2 is shown.

[0135] exist Fig.28 , the light receiving efficiency of pixel R is represented by the curve metalens×R filter (R) (Metalens×Rfilter(R)). The light receiving efficiency of pixel G is represented by the curve metalens×G filter (G1 or G2) (Metalens×Gfilter(G1or G2)). The light receiving efficiency of pixel B is represented by the curve metalens×B filter (B) (Metalens×Bfilter(B)). The light receiving efficiency of pixel NIR is represented by the curve metalens×NIR filter (NIR) (Metalens×Rfilter(NIR)). As a comparative example, the light receiving efficiency of pixel R in the case where there is no optical element array 120 and only a general filter is set is represented by the curve R filter (R) (R filter(R)). The light receiving efficiency of pixel G is represented by the curve G filter (G1 or G2) (G filter(G1or G2)). The light receiving efficiency of pixel B is represented by the curve B filter (B) (Bfilter(B)). The light receiving efficiency of the pixel NIR is represented by a curve NIR filter (NIR) (filter (NIR)). In addition, the sensitivity spectrum of each pixel of the RGB-IR sensor provided with only the filter described as a comparative example is referred to in Reference 1.

[0136] Reference 1: Y. Monno, H. Teranaka, K. Yoshizaki, M. Tanaka, & M. Okutomi, (2018). "Single-sensor RGB-NIR imaging: High-quality system design and prototype implementation". IEEE Sensors Journal, 19(2), 497-507.

[0137] The peak values ​​of the spectra of pixel R, pixel G, pixel B, and pixel NIR are also about 1.5 to 1.9 times that of the comparative example, and a greater light receiving efficiency can be obtained than that of the comparative example. The total transmittance is also 39.4%, which exceeds 32.9% (about 1.20 times) of the comparative example. In addition, the spectrum of light incident on each pixel is also sharper than that of the comparative example, and it can also be seen that other unnecessary wavelength components can be reduced accordingly. As a result, color reproducibility is improved.

[0138] [Effects of Embodiment 2]

[0139] As described above, according to the image sensor 200 further including the filter layer 170 , it is possible to improve the light receiving efficiency and further improve the color reproducibility.

[0140] [Variation of Embodiment 2]

[0141] Figure 29 to Figure 32 1 is a diagram showing an example of a schematic structure of an image pickup element according to a modified example of Embodiment 2. Fig.29 and Fig.30 As shown in the imaging element 200A of FIG. 1 , a near infrared absorption filter 170A may be provided in place of the filter layer 170. Fig.31 and Fig.32 As shown in the imaging element 200B, a near infrared absorption filter layer 170A may also be provided above (or below) the filter layer 170. The near infrared absorption filter layer 170A has a filter 170NIR that absorbs near infrared light and is provided in a manner that covers only the pixels R, G, and B, only directly above the pixels R, G, and B. In this way, by providing the near infrared absorption filter layer 170A only directly above the pixels R, G, and B, the incidence of near infrared light, which is the main cause of noise, on the pixels R, G, and B can be suppressed. In addition, since the pixel NIR needs to receive near infrared light, the filter 170NIR is not provided on the pixel NIR.

[0142] In addition, in embodiments 1 and 2, TiO2 and SiN are used as examples of materials for the structure 160. However, the material of the structure 160 is not limited thereto. For example, for light with a wavelength of 380nm to 1000nm (visible light to near-infrared light), in addition to SiN, SiC, TiO2, GaN, etc. can also be used as the material of the structure 6. These materials are suitable because of their high refractive index and low absorption loss. When using light with a wavelength of 800 to 1000nm (near-infrared light), Si, SiC, SiN, TiO2, GaAs, GaN, etc. can be used as the material of the structure 6. These materials are suitable because of their low loss. For light in the long-wave near-infrared light region (1.3μm, 1.55μm, etc. as communication wavelengths), in addition to the above-mentioned materials, InP, etc. can also be used as the material of the structure 160.

[0143] When the structure 160 is formed by pasting, coating, or the like, examples of the material include polyimides such as fluorinated polyimide, BCB (benzocyclobutene), photocurable resins, UV epoxy resins, acrylic resins such as PMMA, polymers such as resists, and the like.

[0144] In addition, in Embodiments 1 and 2, examples are shown in which SiO2 and an air layer are assumed as the material of the transparent layer 5, but the present invention is not limited thereto. It also includes general glass materials, etc., as long as it has a refractive index lower than that of the material of the structure 6 and has a low loss relative to the wavelength of the incident light. The transparent layer 5 can be made of the same material as the color filter as long as it has a sufficiently low loss for the wavelength of the light that should reach the corresponding pixel, for example, it can also be an organic material such as resin. In this case, the transparent layer 5 is not only the same material as the color filter, but also has the same structure as the color filter, and can also be designed to have an absorption characteristic corresponding to the wavelength of the light that should be guided to the corresponding pixel.

[0145] In addition, in embodiments 1 and 2, the colors corresponding to pixels are described using the three primary colors of RGB and near-infrared light as examples, but pixels can also correspond to near-infrared light and light of wavelengths other than the three primary colors (for example, infrared light, ultraviolet light, etc.).

[0146] In addition, in Embodiments 1 and 2, an example of using a structure having three different cross-sectional shapes such as a square shape, an X shape, and a hollow rhombus is described as the shape of the structure 160. This shape is an example, and two structures (e.g., only a square shape and an X shape) may be used, or four or more structures may be used.

[0147] As mentioned above, although this invention was demonstrated based on the specific embodiment, this invention is not limited to the said embodiment, Of course, various changes can be made within the range which does not deviate from the summary.

[0148] The above-described technology is determined, for example, by the following method. Figure 1 to Figure 5 , Fig.23 as well as Fig.24 As described in the above, the optical element array 120 comprises: a transparent layer 150, which is used to cover a plurality of pixels each including a photoelectric conversion element; and a plurality of structures 160, which are arranged on the transparent layer 150 or in the transparent layer 150 in the surface direction (XY plane direction) of the transparent layer 150, and the plurality of structures 160 are arranged to converge the first light with a wavelength in the near-infrared light region in the incident light to the first pixel (pixel NIR) among the above-mentioned plurality of pixels, and to converge the light of a second color (for example, blue) with a wavelength in a region outside the near-infrared light region to the second pixel (for example, pixel B).

[0149] The above-mentioned optical element array 120 has both the function of separating the wavelengths in the near-infrared light region from the wavelengths in other regions and the lens function (light-focusing function). Therefore, compared with, for example, providing a filter (such as a color filter) corresponding to each pixel and further providing a microlens, the light receiving efficiency of the incident light in the pixel, the visible light and the near-infrared light, can be greatly improved, and the light receiving sensitivity can be improved. In addition, since the structure is simplified, the manufacturing cost can also be reduced. Since a plurality of structures 160 can be arranged without gaps in the plane, the aperture ratio is also increased compared to a microlens. The color separation function and the lens function are not limited to the function of separating and converging the wavelengths in the near-infrared light region and the wavelengths in other regions, and can also correspond to near-infrared light, three-color light or two-color light.

[0150] As reference Figure 1 to Figure 5 , Fig.23 as well as Fig.24 As described in , etc., the optical element array 120 may also include: a transparent layer 150 for covering a plurality of pixels each including a photoelectric conversion element; and a plurality of structures 160, which are arranged on the transparent layer 150 or in the transparent layer 150 in the surface direction (plane direction) of the transparent layer 150, and output a first light having a wavelength in the near-infrared region among the incident light, and output a second color light having a wavelength in a region outside the near-infrared region among the incident light. Thus, the optical element array 120 has a function of separating wavelengths in the near-infrared region from wavelengths in other regions.

[0151] As reference Figure 10 to Figure 15As described in, for example, each of the plurality of structures 160 may be a columnar structure having a refractive index higher than that of the transparent layer 5 and providing an optical phase delay amount corresponding to the cross-sectional shape to the incident light. Figure 16 to Figure 21 As described in the above, the plurality of structures 160 can be arranged in accordance with the optical phase delay distribution for realizing the above-mentioned focusing. For example, by arranging such a plurality of structures 160, both the wavelength separation function and the lens function can be realized.

[0152] As reference Figure 5 and Fig.25 As described in the above, the cross-sectional shape of each of the plurality of structures 160 may be a four-fold rotationally symmetric shape. This can prevent polarization dependency from occurring.

[0153] As reference Figure 6 to Figure 9 As described in the above, the plurality of structures 6 may be arranged so that light of a wavelength corresponding to one pixel among light incident on the outside of the region opposite to one pixel is also focused on the one pixel. Thus, the amount of received light can be increased compared to the case where only light incident on the region opposite to one pixel is focused on the pixel.

[0154] Reference Figure 1 to Figure 5 The imaging element 100 described in the above is also one embodiment of the present disclosure. The imaging element 100 includes an optical element array 120 and a plurality of pixels 130 (such as pixel NIR) covered by a transparent layer 150. As described above, the manufacturing cost can be reduced. The light receiving sensitivity can also be improved and the aperture ratio can be increased.

[0155] As reference Fig.26 and Fig. 27 As described in , etc., the image sensor 200 may include a filter layer 170 provided between a plurality of pixels (pixel NIR, etc.) and the transparent layer 150. This can improve light receiving efficiency and further improve color reproducibility.

[0156] And, as referenced Figure 29 to Figure 32 As described above, the imaging elements 200A and 200B may be provided with a near infrared absorption filter 170A, which is provided only on the second pixel. A near infrared absorption filter that absorbs near infrared light may also be provided just above the second pixel (pixel R, pixel G, pixel B), so as to suppress the incidence of near infrared light, which is a major cause of noise, on the second pixel (pixel R, pixel G, pixel B).

[0157] Reference Figure 1The imaging device 10 described in the above is also one embodiment of the present disclosure. The imaging device 10 includes the imaging element 12 and a signal processing unit 13 that generates an image signal based on the electrical signal obtained from the imaging element 12 and the pixel signal. As described above, the manufacturing cost can be reduced. The light receiving sensitivity can also be improved and the aperture ratio can be increased.

[0158] Description of Reference Numerals

[0159] 1 Object

[0160] 10. Camera

[0161] 11 Lens Optical System

[0162] 12, 100, 100A, 100B, 200 Imaging components

[0163] 13 Signal Processing Unit

[0164] 110 pixel array

[0165] 120 optical element array

[0166] 130 pixels

[0167] 150, 150A transparent layer

[0168] 160 Structure

[0169] 170 filter layer

[0170] 180 Wiring Layer

[0171] 190 transparent substrate

Claims

1. An optical element, characterized in that: have: a transparent layer for covering a plurality of pixels each including a photoelectric conversion element; and a plurality of structures arranged on or in the transparent layer in the surface direction of the transparent layer, The plurality of structures are configured to focus first light having a wavelength in a near-infrared region among incident light on a first pixel among the plurality of pixels, and focus second color light having a wavelength in a region outside the near-infrared region on a second pixel, The plurality of structures are arranged so as to also focus light having a wavelength corresponding to one pixel, among light incident on the outside of a region facing one pixel, on the one pixel.

2. The optical element according to claim 1, characterized in that Each of the plurality of structures is a columnar structure having a refractive index higher than that of the transparent layer and providing an optical phase delay amount corresponding to a cross-sectional shape to incident light. The cross-sectional shapes of the plurality of structures are set according to a light phase delay amount distribution for realizing the convergence, and the plurality of structures are arranged according to a light phase delay amount distribution for realizing the convergence.

3. The optical element according to claim 1 or 2, characterized in that: The cross-sectional shape of each of the plurality of structures is a four-fold rotationally symmetric shape.

4. An imaging element, characterized in that: The imaging element has: The optical element according to claim 1 or 2; and The plurality of pixels are covered by the transparent layer.

5. The imaging element according to claim 4, wherein: The imaging element includes a filter layer provided between the plurality of pixels and the transparent layer.

6. The imaging element according to claim 5, wherein: The filter layer is a near infrared absorption filter provided only on the second pixel.

7. A camera device, characterized in that: The camera device comprises: The imaging element according to claim 4; and A signal processing unit generates an image signal based on the electric signal obtained from the imaging element.

Images