Light detection device and light detection system

Abstract

The present disclosure relates to a light detection device and a light detection system which make it possible to achieve both size reduction and noise immunity of an optical system. In this light detection device, a transparent substrate, a metasurface element, a band-pass filter, and a sensor substrate are arranged in this order. The metasurface element deflects incident light transmitted through the transparent substrate such that the incident light is substantially perpendicularly incident on the band-pass filter. The band-pass filter transmits only light in a specific wavelength band of the incident light. The sensor substrate photoelectrically converts the light in the specific wavelength band and outputs a signal corresponding to the amount of the light. The ratio D / S between a distance D from the metasurface element to the sensor substrate and a pixel size S of the sensor substrate is 40 or less. The technology of the present disclosure can be applied to, for example, a light detection device that emits infrared light as irradiation light and detects reflected light which is the irradiation light reflected by a predetermined subject.

Description

Optical detection device and optical detection system

[0001] The present disclosure relates to a photodetector and a photodetection system, and more particularly to a photodetector and a photodetection system that can achieve both a compact optical system and noise resistance.

[0002] In a distance measurement system that uses the ToF (Time-of-Flight) method, a light source emits infrared light as active light onto the object to be measured, and the light that is reflected by the object is received by a light receiving device to measure the distance to the object. In such a system that uses active light, ambient light such as sunlight outdoors becomes noise, which worsens the signal-to-noise ratio during measurement.

[0003] To effectively block noise light other than the active light, it is possible to use a bandpass filter that transmits only light of a desired wavelength. Bandpass filters are known to have a large loss of light when the light is incident obliquely, so it is desirable to make the incident light approximately perpendicular to the bandpass filter.

[0004] A telecentric optical system is known as an optical system that corrects incident light so that it is incident approximately perpendicularly, but if telecentricity is achieved using only the optical system, the size of the optical system becomes large.

[0005] Patent Document 1 discloses an imaging system having a metasurface layer (metasurface) and a narrow-bandwidth optical filter between a substrate layer and one image sensor.

[0006] Special Publication No. 2022-542172

[0007] The greater the distance from the metasurface to the image sensor, the greater the adverse effect of metasurface aberration on the optical system. Therefore, it is desirable to make the distance from the metasurface to the image sensor as close to zero as possible. However, the structure of Patent Document 1 does not specify the distance from the metasurface to the image sensor. Therefore, the adverse effect of metasurface aberration on the optical system cannot be eliminated.

[0008] The present disclosure has been made in view of the above circumstances, and aims to achieve both miniaturization and noise resistance in an optical system.

[0009] The photodetector device of the first aspect of the present disclosure comprises a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate arranged in that order; the metasurface element deflects incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly to the bandpass filter; the bandpass filter transmits only light of a specific wavelength band of the incident light; the sensor substrate photoelectrically converts the light of the specific wavelength band and outputs a signal corresponding to the amount of light; and the ratio D / S of the distance D from the metasurface element to the sensor substrate and the pixel size S of the sensor substrate is configured to be 40 or less.

[0010] An optical detection system according to a second aspect of the present disclosure includes a light source device that emits light of a predetermined wavelength as irradiating light; and an optical detection device that detects reflected light of the irradiating light reflected by a predetermined subject, wherein the optical detection device comprises a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate arranged in that order, wherein the metasurface element deflects incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly to the bandpass filter, the bandpass filter transmits only light of a specific wavelength band of the incident light, the sensor substrate photoelectrically converts the light of the specific wavelength band and outputs a signal corresponding to the amount of light, and the ratio D / S of the distance D from the metasurface element to the sensor substrate and the pixel size S of the sensor substrate is configured to be 40 or less.

[0011] In the first and second aspects of the present disclosure, a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate are arranged in that order, and in the metasurface element, incident light transmitted through the transparent substrate is deflected so as to be incident approximately perpendicularly on the bandpass filter, and only light of a specific wavelength band of the incident light is transmitted through the bandpass filter, and in the sensor substrate, the light of the specific wavelength band is photoelectrically converted to output a signal corresponding to the amount of light. The ratio D / S of the distance D from the metasurface element to the sensor substrate and the pixel size S of the sensor substrate is configured to be 40 or less.

[0012] The light detection device and the light detection system may be stand-alone devices or may be modules that are incorporated into other devices.

[0013] FIG. 7 is a cross-sectional view of a photodetector according to a first embodiment of the present disclosure. FIG. 8 is a cross-sectional view of a photodetector according to a second embodiment of the present disclosure. FIG. 9 is a cross-sectional view of a photodetector according to a third embodiment of the present disclosure. FIG. 10 is a diagram illustrating an effect of the photodetector according to the second embodiment. FIG. 11 is a diagram illustrating an effect of the photodetector according to the third embodiment. FIG. 12 is a cross-sectional view of a photodetector according to a fourth embodiment of the present disclosure. FIG. 13 is a diagram illustrating a configuration example of a photodetection module according to a fifth embodiment of the present disclosure. FIG. 14 is a diagram illustrating an example specification of the module lens of FIG. 7. FIG. 15 is a diagram illustrating characteristic data of a plurality of lenses constituting the module lens of FIG. 7. FIG. 16 is a diagram illustrating an example of longitudinal aberration of the module lens of FIG. 7. FIG. 17 is a diagram illustrating an example of lateral aberration of the module lens of FIG. 7. FIG. 18 is a block diagram illustrating a configuration example of a photodetection system according to a sixth embodiment of the present disclosure.

[0014] Hereinafter, modes for carrying out the technology of the present disclosure (hereinafter referred to as embodiments) will be described with reference to the accompanying drawings. The description will be given in the following order: 1. First embodiment of a photodetector 2. Second embodiment of a photodetector 3. Third embodiment of a photodetector 4. Fourth embodiment of a photodetector 5. Summary of a photodetector 6. Example of a configuration of a photodetection module 7. Example of a configuration of a photodetection system

[0015] In this specification and drawings, identical or similar parts are denoted by identical or similar reference numerals, and redundant explanations are omitted as appropriate. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc. may differ from the actual ones. Furthermore, there may be parts in which the dimensional relationships and ratios differ between the drawings.

[0016] Furthermore, the definitions of directions such as up and down in the following description are merely for the convenience of explanation and do not limit the technical idea of ​​the present disclosure. For example, if an object is rotated 90 degrees and observed, up and down are converted to left and right and read, and if it is rotated 180 degrees and observed, up and down are read inverted.

[0017] 1. First Embodiment of Photodetector FIG. 1 is a cross-sectional view of a photodetector according to a first embodiment of the present disclosure.

[0018] The photodetector 1 shown in FIG. 1 detects light from a subject and generates and outputs a signal corresponding to the amount of light. The photodetector 1 is configured by stacking a transparent substrate 12, a metasurface element (metasurface layer) 13, and a bandpass filter 14 on the light incident surface side of a sensor substrate 11. In FIG. 1 , the upper surface of the sensor substrate 11 is the light incident surface of the sensor substrate 11, and the transparent substrate 12, metasurface element 13, and bandpass filter 14 are stacked in this order from the top layer farthest from the sensor substrate 11. An air gap (air layer) 15 is formed between the bandpass filter 14 and the sensor substrate 11 using a spacer (not shown) or the like. An adhesive or the like may be inserted into at least a portion of the air gap 15 (e.g., the outer periphery in a plan view), and the bandpass filter 14 and the sensor substrate 11 may be bonded together. Alternatively, an adhesive may be embedded in the entire air gap 15 layer, and the bandpass filter 14 and the sensor substrate 11 may be bonded together. From the viewpoint of suppressing unnecessary reflections and the like at the air gap 15 and suppressing stray light, it is desirable to fill the entire layer of the air gap 15 with adhesive.

[0019] The sensor substrate 11 is a substrate having a pixel array section in which pixels, each having a photoelectric conversion section such as a photodiode formed on a semiconductor substrate such as a silicon substrate, are arranged two-dimensionally in a matrix, and performs photoelectric conversion on incident light to output a pixel signal corresponding to the amount of light. For example, a microlens array is provided on the upper surface (light incident surface) of the sensor substrate 11. An anti-reflection film may be formed on the upper surface of the microlens array. A cover glass may be provided on the top surface of the sensor substrate 11, but since the transparent substrate 12 is also provided, it is preferable not to have a cover glass.

[0020] The transparent substrate 12 is a substrate that transmits incident light and protects the underlying sensor substrate 11, etc. The transparent substrate 12 is made of, for example, a glass substrate, etc. An anti-reflection film, for example, may be formed between the transparent substrate 12 and the metasurface element 13, such as on the lower surface of the transparent substrate 12.

[0021] The metasurface element 13 is composed of an array of pillars 21, which are nano-level microstructures (nanostructures). The metasurface element 13 locally changes the phase difference of light by varying at least one of the diameter, pitch, and shape of the pillars 21, which are machined into a columnar shape. As shown by the dashed lines in FIG. 1 , the metasurface element 13 has a prism function that bends incident light (oblique incident light) from a module lens (e.g., module lens 111 in FIG. 7 ) having a predetermined principal angle of incidence by the principal angle of incidence at each pixel. As a result, the metasurface element 13 emits incident light approximately perpendicularly. Here, approximately perpendicular means, for example, that the principal ray of the incident light is in the range of 0°±10° with respect to the plane of the sensor substrate 11. The diameter (thickness), pitch, and shape of the pillars 21 vary depending on the pixel position within the pixel array section of the sensor substrate 11, in other words, the image height position. That is, in the metasurface element 13, the amount of phase delay to be imparted for each image height position is determined, and the determined amount of phase delay determines the diameter, pitch, and shape of the pillars 21. A predetermined filler material 22 is embedded between the multiple arranged pillars 21 as an inter-pillar medium.

[0022] In addition to the prism function described above, the metasurface element 13 may be designed to have a lens function to focus incident light. By providing the metasurface element 13 with a lens function, the range of incident angles of the incident light can be narrowed, and only light close to perpendicular incidence can be made to enter the bandpass filter 14, thereby increasing the effect of improving the SNR through noise suppression.

[0023] 1, in the photodetector 1, the distance D from the metasurface element 13 to the sensor substrate 11 is set so that the ratio D / S of the distance D from the surface of the metasurface element 13 closest to the sensor substrate 11 to the upper surface of the sensor substrate 11 to the pixel size S of the sensor substrate 11 is 40 or less (D / S≦40). For example, if the pixel size S of the sensor substrate 11 is 10 μm square, then D=40×0.01=0.4, and the distance D from the metasurface element 13 to the sensor substrate 11 is set to within 0.4 mm. From the viewpoint of further suppressing degradation of optical characteristics, it is more preferable to set the ratio D / S of the distance D to the pixel size S to 20 or less (D / S≦20).

[0024] For example, when the light to be photoelectrically converted is infrared light, the material of the pillars 21 is preferably α-Si (amorphous silicon), poly-Si (polysilicon), or germanium. When the light to be photoelectrically converted is visible light, the material is preferably one of titanium oxide, niobium oxide, tantalum oxide, aluminum oxide, hafnium oxide, silicon nitride, silicon oxide, silicon nitride oxide, silicon carbide, silicon oxide carbide, silicon nitride carbon, or zirconium oxide, or a laminate structure thereof. Silicon nitride oxide, silicon oxide carbide, and silicon nitride carbon are included in the category of polycrystalline silicon. The material of the filler 22 can be organic or inorganic. Examples of organic materials include siloxane-based resins, styrene-based resins, acrylic resins, styrene-acrylic copolymer resins, F-containing materials of any of these resins, and materials in which beads with a refractive index lower than that of the resin are embedded in any of these resins. Examples of inorganic materials include SOG (Spin On Glass), silicon oxide, niobium oxide, tantalum oxide, aluminum oxide, hafnium oxide, silicon nitride, silicon nitride oxide, silicon carbide, silicon carbide oxide, silicon carbide nitride, zirconium oxide, and stacked structures thereof.

[0025] The bandpass filter 14 is a filter that transmits only light in a specific wavelength band near the target wavelength. The bandpass filter 14 transmits only light in the specific wavelength band from the light incident from the metasurface element 13 at a substantially normal angle, and allows it to enter the sensor substrate 11. If the target wavelength is, for example, 940 nm in the infrared region, the bandpass filter 14 transmits light in the wavelength band from 935 nm to 945 nm as the specific wavelength band. Narrowing the transmission wavelength band of the bandpass filter 14 reduces noise but also reduces the amount of light. Therefore, the signal-to-noise ratio can be improved by setting the transmission wavelength bandwidth so that the amount of light is not significantly reduced. A width of 10 nm is set as the transmission wavelength bandwidth, which is less affected by the reduction in light amount.

[0026] The sensor substrate 11 photoelectrically converts light in a specific wavelength band that has passed through the bandpass filter 14 and outputs a signal (light detection signal) that corresponds to the amount of light.

[0027] In the photodetector 1 configured as described above, the metasurface element 13 deflects obliquely incident light so that it is incident approximately perpendicularly on the bandpass filter 14, thereby achieving telecentricity. This eliminates the need to achieve telecentricity in any part other than the metasurface element 13, allowing for a more compact optical system than would be possible if telecentricity were achieved solely through the optical system. Furthermore, the distance D from the metasurface element 13 to the sensor substrate 11 is configured to be short, with the ratio D / S to the pixel size S being 40 or less. By keeping the distance D from the metasurface element 13 to the sensor substrate 11 within a predetermined value (D / S≦40), the incident light can be corrected to be approximately perpendicularly incident while suppressing the adverse effects of aberration degradation caused by the metasurface element 13. This is particularly effective in suppressing the adverse effects of chromatic aberration caused by the metasurface element 13 when a light source with a finite bandwidth, such as an LED light source, is used as the light source for active light. It is known that the bandpass filter 14 suffers significant light loss when incident at an oblique angle, so it is desirable to have the incident light incident approximately perpendicularly on the bandpass filter 14. The metasurface element 13 allows light to be incident on the bandpass filter 14 substantially perpendicularly, so that light that becomes noise outside the target wavelength, such as outdoor sunlight, can be effectively blocked. Therefore, the photodetector 1 according to the first embodiment shown in FIG. 1 can achieve both a compact optical system and noise resistance.

[0028] 2. Second Embodiment of Photodetector FIG. 2 is a cross-sectional view of a photodetector according to a second embodiment of the present disclosure.

[0029] The photodetector 1 of the second embodiment, like the first embodiment shown in FIG. 1 , is configured by stacking a transparent substrate 12, a metasurface element 13, and a bandpass filter 14 on the light incident surface side of a sensor substrate 11. Similar to the first embodiment, the transparent substrate 12, the metasurface element 13, and the bandpass filter 14 are stacked in that order on the sensor substrate 11 from the top side in the figure where light is incident. On the other hand, the photodetector 1 of the second embodiment differs from the first embodiment in the configuration of the metasurface element 13. Specifically, in the second embodiment, the diameter (thickness) of the pillars 21 of the metasurface element 13 is small, and the spacing (pitch) between the pillars 21 is also large. Furthermore, end members 23 made of a different material from the pillars 21 are formed at the tips (ends) of the pillars 21 on the sensor substrate 11 side. These end members 23 are made of a hard mask material used in etching to form the pillars 21. The end member 23 is made of the inorganic material described above that can be used for the filler 22, such as silicon oxide, silicon nitride, or silicon nitride oxide. The end member 23 may be made of the same material as the filler 22 or a different material. When a material different from the filler 22 is used for the end member 23, it is desirable to use a material with a refractive index similar to that of the filler 22, so that the difference in refractive index between the end member 23 and the filler 22 is within a predetermined value (for example, within 0.2). In addition, in the first embodiment, the height of the pillar 21 was the same as the height (thickness) of the entire metasurface element 13. However, in the second embodiment, the thickness of the filler 22 is greater than the combined thickness of the pillar 21 and the end member 23, and the filler 22 is formed to cover the tip of the pillar 21 on the sensor substrate 11 side. In such a configuration of the metasurface element 13, the metasurface element 13 is arranged so that the ratio D / S of the distance D from the tip surface of the pillar 21 of the metasurface element 13 on the sensor substrate 11 side to the sensor substrate 11 and the pixel size S is 40 or less (D / S≦40).

[0030] 3. Third Embodiment of Photodetector FIG. 3 is a cross-sectional view of a photodetector according to a third embodiment of the present disclosure.

[0031] The photodetector 1 of the third embodiment, like the first embodiment shown in FIG. 1 , is configured by stacking a transparent substrate 12, a metasurface element 13, and a bandpass filter 14 on the light incident surface side of a sensor substrate 11. Similar to the first embodiment, the transparent substrate 12, the metasurface element 13, and the bandpass filter 14 are stacked on the sensor substrate 11 in that order from the top side in the figure where light is incident. Also, like the second embodiment shown in FIG. 2 , the diameter of the pillars 21 of the metasurface element 13 is small, the spacing between the pillars 21 is larger than in the first embodiment, and the filler 22 is formed to cover the tips of the pillars 21 on the sensor substrate 11 side. In the third embodiment, the metasurface element 13 is also arranged so that the ratio D / S of the distance D from the tip surface of the pillar 21 of the metasurface element 13 to the sensor substrate 11 and the pixel size S is 40 or less (D / S≦40). On the other hand, the photodetector 1 of the third embodiment differs from the first embodiment in that a graded layer 31 is added between the metasurface element 13 and the transparent substrate 12 .

[0032] The graded layer 31 contains the material of the pillars 21, and the content of the material gradually changes from the transparent substrate 12 toward the metasurface element 13, so that the refractive index changes gently from the transparent substrate 12 toward the metasurface element 13. For example, the pillars 21 are made of silicon, and the graded layer 31 is made of silicon oxide (SiO2), and the silicon content in the graded layer 31 is formed so as to gradually increase from the surface on the transparent substrate 12 side toward the surface of the metasurface element 13.

[0033] When the metasurface element 13 and the bandpass filter 14 are formed on the same surface of the transparent substrate 12 (the surface on the sensor substrate 11 side) as in the first to third embodiments, there is a risk that the pillars 21 will collapse during the process of embedding the filler material 22 in the gaps between the pillars 21.

[0034] In the second embodiment, as shown in FIG. 4A, a material for the end members 23 is formed as a hard mask on the upper surface of a pillar material layer (e.g., silicon) 21A formed on the upper surface of a transparent substrate 12 and patterned. Then, as shown in FIG. 4B, the pillar material layer 21A is etched based on the patterned hard mask to form pillars 21. After the pillars 21 are formed, as shown in FIG. 4C, a filler material 22 is filled into the gaps and upper layers of the pillars 21, completing the metasurface element 13. Therefore, the end members 23 are the hard mask that remains unremoved. Although the hard mask may be removed, it can be left intact by using the same material as the filler material 22 or a different material with a similar refractive index. Leaving the hard mask intact eliminates the mask removal process, which carries a high risk of pillar collapse.

[0035] In the third embodiment, as shown in FIG. 5A, a pillar material layer 21B is formed on the upper surface of the transparent substrate 12. The pillar material layer 21B is formed so that the ratio of silicon (Si) to oxygen (O) (Si / O ratio) is small in the layer closer to the transparent substrate 12 and gradually increases toward the upper layer. The upper layer of the pillar material layer 21B is formed solely of silicon. For convenience of explanation, FIG. 5 illustrates a boundary between the lower layer of the pillar material layer 21B, which contains at least a portion of oxygen (O), and the upper layer, which is formed solely of silicon. However, in reality, there is no boundary, and the pillar material layer 21B is formed integrally. Then, as shown in FIG. 5B, the upper layer portion of the pillar material layer 21B, which is formed solely of silicon, is etched based on a patterned hard mask (not shown), thereby forming the pillar 21. The flat layer portion of the pillar material layer 21B that is not etched becomes the graded layer 31. After the pillars 21 are formed, as shown in Fig. 5C, the gaps between the pillars 21 and the upper layer are filled with filler material 22, thereby completing the metasurface element 13. The pillars 21 and the graded layer 31 are originally one pillar material layer 21B, and the base of the pillars 21 is connected to the graded layer 31, which reduces the risk of the pillars collapsing, such as breaking from the base, during the process of forming the pillars 21 or subsequent processes.

[0036] In addition, the photodetector 1 may be configured by combining the second and third embodiments, i.e., an end member 23 is formed at the tip of the pillar 21, and a graded layer 31 is arranged between the metasurface element 13 and the transparent substrate 12.

[0037] 4. Fourth Embodiment of Photodetector FIG. 6 is a cross-sectional view of a photodetector according to a fourth embodiment of the present disclosure.

[0038] The photodetector 1 of the fourth embodiment, like the first embodiment shown in FIG. 1 , is configured by stacking a transparent substrate 12, a metasurface element 13, and a bandpass filter 14 on the light incident surface side of a sensor substrate 11. Similar to the first embodiment, the transparent substrate 12, the metasurface element 13, and the bandpass filter 14 are stacked on the sensor substrate 11 in that order from the top side in the figure where light is incident. However, the photodetector 1 of the fourth embodiment differs from the first embodiment in the position of the air gap 15. Specifically, in the first embodiment, the air gap 15 was provided between the bandpass filter 14 and the sensor substrate 11. In contrast, in the fourth embodiment, the air gap 15 is provided between the metasurface element 13 and the bandpass filter 14. In the first embodiment, the bandpass filter 14 was formed on the metasurface element 13 on the same surface (the surface facing the sensor substrate 11) of the transparent substrate 12, but in the fourth embodiment, it is formed on the sensor substrate 11. The distance D from the metasurface element 13 to the sensor substrate 11 is configured to be a short distance with a ratio D / S to the pixel size S of 40 or less, as in the first embodiment.

[0039] As described above, the photodetector 1 may be configured so that the metasurface element 13 is formed on the transparent substrate 12 and the bandpass filter 14 is formed on the sensor substrate 11.

[0040] 5. Summary of the Photodetector The photodetector 1 is configured by arranging, in this order from the light incident side, a transparent substrate 12, a metasurface element 13, a bandpass filter 14, and a sensor substrate 11. The metasurface element 13 deflects incident light that has passed through the transparent substrate 12 in accordance with the image height position, causing the light to be incident approximately perpendicularly on the bandpass filter 14. The bandpass filter 14 transmits only light of a specific wavelength band from the incident light deflected by the metasurface element 13. The sensor substrate 11 photoelectrically converts the light of the specific wavelength band that has passed through the bandpass filter 14 and outputs a signal corresponding to the amount of light. The ratio D / S of the distance D from the metasurface element 13 to the pixel size S of the sensor substrate 11 is configured to be 40 or less.

[0041] It is known that the bandpass filter 14 has a large loss of light intensity when incident at an angle, and it is therefore desirable to make the incident light approximately perpendicular to the bandpass filter 14. By making the metasurface element 13 with a prism function so that the incident light is approximately perpendicular to the bandpass filter 14, the bandpass filter 14 can effectively block light other than the target wavelength.

[0042] The metasurface element 13 allows the optical system to be made smaller than when telecentricity is achieved using only the optical system. Furthermore, by keeping the distance D from the metasurface element 13 to the sensor substrate 11 at a short distance, where the ratio D / S to the pixel size S is 40 or less, the adverse effects of aberration degradation caused by the metasurface element 13 can be suppressed while correcting the incident light to be approximately perpendicularly incident. In addition to the function of deflecting the incident light that has passed through the transparent substrate 12 so that it is approximately perpendicularly incident, the metasurface element 13 may also have a lens function to focus the incident light.

[0043] As described above, the photodetector 1 according to each embodiment can achieve both a compact optical system and noise resistance.

[0044] 6. Configuration Example of Light Detection Module FIG. 7 shows a configuration example of a light detection module according to a fifth embodiment of the present disclosure.

[0045] The light detection module 100 in FIG. 7 is composed of the above-described light detection device 1 and a module lens 111 arranged on the object side of the light detection device 1.

[0046] The photodetector 1 is composed of a sensor substrate 11 and a sealing glass 121. The sealing glass 121 is configured by laminating a transparent substrate 12, a metasurface element 13, and a bandpass filter 14, for example, as shown in FIG. 1 as the first embodiment. Therefore, the sealing glass 121 has a function to protect the sensor substrate 11, a prism function to change the direction of incident light so that it is incident approximately perpendicularly, and a bandpass filter function to transmit light in a specific wavelength band. Note that the photodetector 1 may adopt any of the second to fourth embodiments instead of the configuration of the first embodiment shown in FIG. 1.

[0047] The module lens 111 is composed of three lenses L, namely, a first lens L1, a second lens L2, and a third lens L3, in order from the object side. The dashed-dotted line indicates the center of the optical axis. The first lens L1 has positive refractive power, and the second lens L2 and the third lens L3 have negative refractive power.

[0048] The module lens 111 focuses light rays from the object side and forms an image on the photoelectric conversion unit of the sensor substrate 11. Because telecentricity is achieved by the metasurface element 13 formed on the sealing glass 121, there is no need to achieve telecentricity with the module lens 111. This allows the photodetection module 100 to have a shorter overall optical length than when telecentricity is achieved by the optical system alone, allowing the optical system to be made smaller (lower in height).

[0049] <Specification Example of Module Lens> FIG. 8 is a diagram showing an example of the specification of the module lens 111. As shown in FIG.

[0050] 8, the module lens 111 is designed to have a focal length of 1.20 mm, an F-number (Fno) of 2.06, an FOV (Field Of View) of 75 degrees, an image height Y of 1.00, and a total lens length L of 1.71 mm. The FOV represents the object-side intake angle of the module lens 111, or the so-called angle of view, and corresponds to an angle of view of 2ω on both sides.

[0051] FIG. 9 is a diagram showing characteristic data of each optical surface of the first lens L1 to the third lens L3 that make up the module lens 111.

[0052] 9, the optical surfaces of the first lens L1 to the third lens L3 are assigned surface numbers, starting with "1" for the object-side surface of the first lens L1 and increasing sequentially toward the image plane, with the surface number of the image plane-side surface of the third lens L3 being "6." Surface number "7" represents the object-side surface of the seal glass 121. The lens is designed assuming that the distance from the first surface of the first lens L1 to the object is 20.0 (d=20.0), and is designed to provide excellent performance at close distances.

[0053] FIG. 9 shows the radius of curvature r of each optical surface corresponding to the surface number, the surface spacing d, the refractive index nd for the d-line (wavelength 588 nm), the Abbe number vd for the d-line, and the effective diameter.

[0054] 9, the radius of curvature r of the optical surface of the first lens L1 with surface number "1" is 0.582 mm, the surface distance d from the optical surface with surface number "2" is 0.28 mm, the refractive index nd is 1.525, the Abbe number vd is 56.0, and the effective diameter is 0.40 mm. The radius of curvature of the optical surface of the first lens L1 with surface number "2" is 1.406, the surface distance from the optical surface with surface number "3" is 0.17 mm, and the effective diameter is 0.27 mm.

[0055] The radius of curvature r of the optical surface of the second lens L2 having surface number "3" is -11.720, the surface distance d from the optical surface of surface number "4" is 0.36 mm, the refractive index nd is 1.525, the Abbe number vd is 56.0, and the effective diameter is 0.33 mm. The radius of curvature r of the optical surface of the second lens L2 having surface number "4" is -0.597, the surface distance d from the optical surface of surface number "5" is 0.28 mm, and the effective diameter is 0.41 mm.

[0056] The radius of curvature r of the optical surface of the third lens L3 with surface number "5" is -1.250, the surface distance d from the optical surface of surface number "6" is 0.20 mm, the refractive index nd is 1.525, the Abbe number vd is 56.0, and the effective diameter is 0.44 mm. The radius of curvature r of the optical surface of the third lens L3 with surface number "6" is 0.843, the surface distance d from the optical surface of surface number "7" is 0.07 mm, and the effective diameter is 0.75 mm.

[0057] The radius of curvature r of the object-side optical surface of the seal glass 121 with surface number "7" is infinity (Inf), the surface spacing d from the image-side surface of the seal glass 121 is 0.35 mm, the refractive index nd is 1.517, the Abbe number vd is 64.2, and the effective diameter is 0.81 mm.

[0058] The aspherical shape of each of the optical surfaces of the first lens L1 to the third lens L3 can be expressed by the following formula (1).

[0059]

[0060] In formula (1), r represents the distance from the optical axis, Z(r) represents the amount of sag (depth of the aspherical surface) at the distance r from the optical axis, C represents the vertex curvature radius, i.e., the reciprocal of the curvature radius r, K represents the conic constant, A ２ｉ is the aspherical coefficient.

[0061] FIG. 10 shows the radius of curvature r, conic constant K, and aspherical coefficient A of equation (1) representing the aspherical shape for each of the optical surfaces of surface numbers "1" to "6" of the first lens L1 to third lens L3. ２ｉ (i=an integer from 2 to 10).

[0062] The optical surface with surface number "1" has a conic constant K and an aspherical coefficient A ４ , A ６ , A ８ , A １０ , A １２ , A １４ , A １６ , A １８ , A ２０ are 0.000000E+00, 9.692227E-02, 6.933810E-01, 4.965787E+01, -4.944275E+02, 2.088066E+03, 2.193793E-02, 6.321459E-01, 0.000000E+00, and 0.000000E+00, respectively.

[0063] The optical surface with surface number "2" has a conic constant K and an aspherical coefficient A ４ , A ６ , A ８ , A １０ , A １２ , A １４ , A １６ , A １８ , A ２０ are 0.000000E+00, 1.668645E+00, -2.075506E+01, 4.463332E+02, -1.059416E+03, -3.708251E+04, 3.053158E+05, 7.884721E+00, 0.000000E+00, and 0.000000E+00, respectively.

[0064] The optical surface with surface number "3" has a conic constant K and an aspherical coefficient A ４ , A ６ , A８ , A １０ , A １２ , A １４ , A １６ , A １８ , A ２０ are 0.000000E+00, -1.165753E+00, -9.115345E+00, 2.131951E+01, 2.996004E+02, -2.963373E+03, -4.920455E+04, 4.101574E+05, 0.000000E+00, and 0.000000E+00, respectively.

[0065] The optical surface with surface number "4" has a conic constant K and an aspherical coefficient A ４ , A ６ , A ８ , A １０ , A １２ , A １４ , A １６ , A １８ , A ２０ are 0.000000E+00, -6.927645E-01, 2.590574E+00, -7.538194E+01, 5.285011E+02, -1.851247E+03, 6.324493E+02, 3.331658E+03, 0.000000E+00, and 0.000000E+00, respectively.

[0066] The optical surface with surface number "5" has a conic constant K and an aspherical coefficient A ４ , A ６ , A ８ , A １０ , A １２ , A １４ , A １６ , A １８ , A ２０ are 0.000000E+00, -5.707960E+00, 1.774860E+01, -4.637419E+01, 7.507618E+01, -4.784361E+02, 2.929633E+03, -6.256239E+03, 0.000000E+00, and 0.000000E+00, respectively.

[0067] The optical surface with surface number "6" has a conic constant K and an aspherical coefficient A ４ , A ６ , A８ , A １０ , A １２ , A １４ , A １６ , A １８ , A ２０ are 0.000000E+00, -3.815544E+00, 1.296211E+01, -2.936239E+01, 3.038548E+01, 9.052089E+00, -5.430136E+01, 3.017274E+01, 2.803297E+01, and -2.942792E+01, respectively.

[0068] <Examples of Longitudinal and Transverse Aberrations> FIG. 11 is a diagram showing examples of longitudinal aberrations in the module lens 111 having the characteristics shown in FIGS.

[0069] Fig. 11A is a graph showing longitudinal spherical aberration occurring in the module lens 111. In the graph of Fig. 11A, the horizontal axis represents the shift amount (Focus) [mm] of the focusing position, and the vertical axis represents the ratio of light rays to the pupil.

[0070] FIG. 11B is a graph showing field curvatures that occur in the module lens 111. In the graph of FIG. 11B, the horizontal axis represents the amount of deviation (Focus) [mm] of the focusing position, and the vertical axis represents the image height position. For example, an image height position of 1.00 represents a position at 100% of the image height. The solid line represents the relationship between the amount of deviation between the incident position and the focusing position in the sagittal direction S, and the dashed line represents the relationship between the amount of deviation between the incident position and the focusing position in the tangential direction T. The difference between the amount of deviation between the focusing positions in the sagittal direction S and the tangential direction T is astigmatic.

[0071] Fig. 11C is a graph showing distortion occurring in the module lens 111. In the graph of Fig. 11C, the horizontal axis represents distortion [%], and the vertical axis represents the image height position.

[0072] FIG. 12 is a diagram showing an example of lateral aberration in the module lens 111 having the characteristics shown in FIGS.

[0073] A to E in Figure 12 show the lateral aberration at image height positions of 100% (1.00), 80% (0.80), 40% (0.40), 20% (0.20), and 0% (0.00), respectively. The diagram on the left shows the characteristics in the tangential direction, and the diagram on the right shows the characteristics in the sagittal direction. The "37.5°" in parentheses at the 100% image height position represents the angle of incidence of the incident light at the 100% image height position. The same applies to the parentheses at the other image height positions.

[0074] As can be seen by referring to the longitudinal aberration in FIG. 11 and the lateral aberration in FIG. 12, in the light detection module 100, the module lens 111 is made smaller (lower in height), while the aberration is reduced, and excellent imaging performance is achieved.

[0075] 7. Configuration Example of Light Detection System FIG. 13 is a block diagram showing a configuration example of a light detection system according to the sixth embodiment of the present disclosure.

[0076] The light detection system 200 in FIG. 13 includes a light source device 211 , a detection device 212 , and a system control unit 213 .

[0077] The light source device 211 has a light source driving section 231 and a light emitting module 232 , and the light emitting module 232 includes a light source 241 and a light source side optical system 242 .

[0078] The light source driving unit 231 is configured with, for example, a laser driver or the like, and causes each light-emitting element of the light source 241 to emit light in response to a light emission control signal supplied from the system control unit 213. The light source 241 is configured with, for example, a light source array in which a plurality of light-emitting elements, such as a VCSEL (Vertical Cavity Surface Emitting Laser), are arranged in a planar direction. The light source 241 irradiates the subject 201, which is the object to be observed, with light of a predetermined wavelength as irradiation light in accordance with the control of the light source driving unit 231. As the irradiation light, for example, infrared light with a wavelength of approximately 940 nm is used. The irradiation light may be continuous light or pulsed light that is periodically turned on and off.

[0079] The detection device 212 has a sensor control unit 251 and a light detection module 252, and the light detection module 252 includes a light detection device 261 and a light-receiving-side optical system 262. The light detection module 252 is configured, for example, as the light detection module 100 in Fig. 7. The light detection device 261 has the configuration of the light detection device 1 described above, and the light-receiving-side optical system 262 has the configuration of the module lens 111 described above.

[0080] The sensor control unit 251 is configured by, for example, a processor (CPU), and controls the exposure timing of the photodetector 261 in response to a light-receiving control signal supplied from the system control unit 213. The photodetector 261 performs a light-receiving operation (light-detecting operation) in accordance with the control of the sensor control unit 251.

[0081] The system control unit 213 is configured by, for example, a processor (CPU), and controls the timing of light irradiation by the light source device 211 and the timing of light reception by the detection device 212. Specifically, the system control unit 213 generates a light emission control signal and a light reception control signal so that the timing of light irradiation and the timing of light reception by the detection device 212 are synchronized and the system control unit 213 outputs the signals to the light source drive unit 231 and the sensor control unit 251.

[0082] Illumination light of a predetermined pattern emitted from the light source 241 passes through the light source-side optical system 242 and is irradiated onto the subject 201. The illumination light is reflected by the subject 201, passes through the light receiving-side optical system 262, and enters the photodetector 261. The photodetector 261 receives the reflected light of the illumination light reflected by the subject 201, generates a photodetection signal (pixel signal) based on the received light, and outputs the signal to the sensor control unit 251. The sensor control unit 251 outputs the photodetection signal from the photodetector 261 to an external device, for example, the application processor 202. Alternatively, the sensor control unit 251 may generate various types of information, such as image information or ranging information, based on the photodetection signal from the photodetector 261 and output the information to the application processor 202.

[0083] The application processor 202 performs predetermined information processing using various information, such as a light detection signal (pixel signal), image information, and ranging information output from the detection device 212. For example, the application processor 202 generates an infrared image based on infrared light irradiated onto the subject 201. For example, the application processor 202 generates ranging information for measuring the distance to the subject using a direct ToF method or an indirect ToF method based on the light detection signal output from the detection device 212. For example, the application processor 202 extracts the face area of ​​the user as the subject 201 as a region of interest based on the image information and ranging information, and performs face recognition (face authentication). For example, the application processor 202 detects the face area of ​​the user as the subject 201 based on the image information and performs gaze detection (eye tracking). A commonly known method for gaze detection is the corneal reflex method, which uses infrared light to detect gaze. In the corneal reflex method, infrared light is irradiated to capture an image of the user's eye, and the gaze direction is detected from the position of the infrared light on the captured image, i.e., the positional relationship between the bright spot of the infrared light and the pupil of the user being detected.

[0084] The various information processes described as being performed by the application processor 202 may be performed by the sensor control unit 251 of the detection device 212. For example, if the sensor control unit 251 is configured to generate an infrared image based on infrared light irradiated onto the subject 201, the optical detection system 200 implements an infrared image system. For example, if the sensor control unit 251 is configured to generate distance measurement information to the subject using a direct ToF method or an indirect ToF method and output it to the outside, the optical detection system 200 implements a distance measurement system. For example, if the sensor control unit 251 is configured to detect a user's face area and perform gaze detection, the optical detection system 200 implements a gaze detection system.

[0085] The light detection system 200 described above can be incorporated into an electronic device. Examples of electronic devices equipped with the light detection system 200 include mobile devices such as smartphones, tablets, and personal computers. However, electronic devices that can use the light detection system 200 are not limited to mobile devices.

[0086] In each of the above-described embodiments, an example has been described in which the bandpass filter 14 transmits light in the infrared region and the photodetector 1 detects infrared light. However, the light detected by the photodetector 1 is not limited to light in the infrared region, and may be non-visible light of other wavelengths or light in the visible light region including wavelengths such as R (Red), G (Green), and B (Blue).

[0087] Furthermore, the embodiments of the technology of the present disclosure are not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the technology of the present disclosure. For example, it is possible to adopt a form in which all or part of the above-described multiple embodiments are appropriately combined.

[0088] In this specification, a system refers to a collection of multiple components (devices, modules (components), etc.), regardless of whether all of the components are contained in the same housing. Therefore, multiple devices housed in separate housings and connected via a network, and a single device housed in a single housing with multiple modules, are both systems.

[0089] The effects described in this specification are merely examples and are not intended to be limiting, and there may be effects other than those described in this specification.

[0090] The technology disclosed herein may employ the following configurations: (1) A photodetector comprising a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate arranged in that order, wherein the metasurface element deflects incident light transmitted through the transparent substrate so that it is incident substantially perpendicularly on the bandpass filter, the bandpass filter transmits only light of a specific wavelength band of the incident light, and the sensor substrate photoelectrically converts the light of the specific wavelength band to output a signal corresponding to the amount of light, and wherein a ratio D / S of a distance D from the metasurface element to a pixel size S of the sensor substrate is 40 or less. (2) The photodetector according to (1), wherein the bandpass filter is formed on the same surface as the transparent substrate. (3) The photodetector according to (1), wherein the bandpass filter is formed on the sensor substrate. (4) The photodetector according to any one of (1) to (3), wherein the metasurface element includes a plurality of pillars, a filler material embedded between the plurality of pillars, and an end member formed at the tip of the pillar, and wherein the end member and the filler are made of a material having a refractive index difference within a predetermined value. (5) The photodetector according to any one of (1) to (4), wherein the metasurface element includes a plurality of pillars and a filler material embedded between the plurality of pillars, and further includes a layer between the metasurface element and the transparent substrate, in which the content of the material of the pillars gradually changes. (6) The photodetector according to any one of (1) to (5), wherein the ratio D / S is 20 or less. (7) The photodetector according to any one of (1) to (6), wherein the metasurface element has a function of deflecting incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly, and a lens function of focusing the incident light.(8) An optical detection system including: a light source device that emits light of a predetermined wavelength as irradiating light; and an optical detection device that detects reflected light of the irradiating light reflected by a predetermined subject, wherein the optical detection device comprises a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate arranged in that order; the metasurface element deflects incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly to the bandpass filter; the bandpass filter transmits only light of a specific wavelength band of the incident light; the sensor substrate photoelectrically converts the light of the specific wavelength band and outputs a signal according to the amount of light; and the ratio D / S of the distance D from the metasurface element to the sensor substrate and the pixel size S of the sensor substrate is configured to be 40 or less.

[0091] REFERENCE SIGNS LIST 1 Photodetector, 11 Sensor substrate, 12 Transparent substrate, 13 Metasurface element, 14 Bandpass filter, 15 Air gap, 21 Pillar, 22 Filler, 23 End member, 31 Graded layer, 100 Photodetector module, 111 Module lens, 121 Sealing glass, 200 Photodetector system, 201 Object, 202 Application processor, 211 Light source device, 212 Detector, 213 System control unit, 231 Light source driver, 232 Light-emitting module, 241 Light-emitting source, 242 Light source side optical system, 251 Sensor control unit, 252 Photodetector module, 261 Photodetector, L1 First lens, L2 Second lens, L3 Third lens

Claims

1. A photodetector comprising a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate arranged in that order; the metasurface element deflects incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly to the bandpass filter; the bandpass filter transmits only light of a specific wavelength band of the incident light; the sensor substrate photoelectrically converts the light of the specific wavelength band and outputs a signal according to the amount of light; and the ratio D / S of the distance D from the metasurface element to the sensor substrate and the pixel size S of the sensor substrate is configured to be 40 or less.

2. The photodetector according to claim 1, wherein the bandpass filter is formed on the same surface as the transparent substrate.

3. The photodetector according to claim 1, wherein the bandpass filter is formed on the sensor substrate.

4. The optical detection device described in claim 1, wherein the metasurface element includes a plurality of pillars, a filler material embedded between the plurality of pillars, and an end member formed at the tip of the pillar, and the end member and the filler material are made of materials having a refractive index difference within a predetermined value.

5. The optical detection device of claim 1, wherein the metasurface element includes a plurality of pillars and a filler material embedded between the plurality of pillars, and further includes a layer between the metasurface element and the transparent substrate in which the content of the material of the pillars gradually changes.

6. The photodetector according to claim 1, wherein the ratio D / S is 20 or less.

7. The optical detection device described in claim 1, wherein the metasurface element has the function of deflecting incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly, and the function of a lens that focuses the incident light.

8. An optical detection system comprising: a light source device that emits light of a predetermined wavelength as irradiating light; and an optical detection device that detects reflected light of the irradiating light reflected by a predetermined subject, wherein the optical detection device comprises a transparent substrate, a metasurface element, a bandpass filter, and a sensor substrate arranged in that order; the metasurface element deflects incident light that has passed through the transparent substrate so that it is incident approximately perpendicularly to the bandpass filter; the bandpass filter transmits only light of a specific wavelength band of the incident light; the sensor substrate photoelectrically converts the light of the specific wavelength band and outputs a signal according to the amount of light; and the ratio D / S of the distance D from the metasurface element to the sensor substrate and the pixel size S of the sensor substrate is configured to be 40 or less.

Images