Optical element

Abstract

The present invention provides a photodetector that concentrates irradiated light into a narrow area to suppress the loss of light energy and enable efficient light detection. [Solution] The photodetector element 101 comprises a lens 20, a magnetic element 10 having a first ferromagnetic layer 1, a second ferromagnetic layer 2, and a spacer layer 3 sandwiched between the first ferromagnetic layer 1 and the second ferromagnetic layer 2, and a high refractive index layer 30 having a refractive index greater than that of the lens 20 between the lens 20 and the magnetic element 10, and light passing through the lens 20 and the high refractive index layer 30 is irradiated onto the magnetic element 10.

Description

Technical Field

[0001] The present invention relates to a light detection element.

Background Art

[0002] Photoelectric conversion elements such as light detection elements are used in various applications. For example, Patent Document 1 describes a receiving device that receives an optical signal using a photodiode. A photodiode is, for example, a pn junction diode using a semiconductor pn junction or the like, and converts light into an electrical signal. Further, for example, Patent Document 2 describes an optical sensor using a semiconductor pn junction and an image sensor using this optical sensor.

[0003] Furthermore, for example, Patent Document 3 discloses an optical sensor using a magnetic element and a receiving device using this optical sensor, and Patent Document 4 discloses a technique in which a metalens is combined with an optical sensor using a magnetic element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] While photodetectors using semiconductor pn junctions are widely used, new photodetectors are needed for further development. Furthermore, when a photodetector is very small, it is necessary to concentrate the light into a narrow area and reduce the size of the light spot in order to improve the energy efficiency of the light illuminating the photodetector.

[0006] This invention has been made in view of the above problems, and aims to provide a photodetector that concentrates irradiated light into a narrow area to suppress the loss of light energy and perform efficient light detection. [Means for solving the problem]

[0007] To achieve the above objective, the photodetector according to the present invention comprises a lens, a magnetic element having a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first and second ferromagnetic layers, and a high refractive index layer provided between the lens and the magnetic element and having a refractive index greater than that of the lens, wherein light passing through the lens and the high refractive index layer is irradiated onto the magnetic element.

[0008] This configuration allows the light sensing element of the present invention to pass through a high refractive index layer, which has a higher refractive index than the lens, thereby reducing the spot size of light irradiating the magnetic element. By reducing the spot size of the light, the thermal energy generated by the light can be efficiently absorbed by the magnetic element, thereby improving the sensitivity of the light sensing element.

[0009] In the photodetector element according to the present invention, the lens may be a metalens comprising a plurality of nanostructures arranged in two dimensions.

[0010] With this configuration, the photodetector element of the present invention uses a metalens comprising multiple nanostructures arranged in two dimensions as the lens, allowing it to be manufactured in a consistent manufacturing process from the magnetic element to the metalens. This simplifies the manufacturing process and enables the creation of tiny lenses suitable for minute magnetic elements.

[0011] The photodetector according to the present invention may include a high thermal conductivity layer between the lens and the magnetic element, which has a higher thermal conductivity than the high refractive index layer.

[0012] With this configuration, the photodetector of the present invention can enhance the heat dissipation of heat generated by the photodetector and the like by incorporating a high thermal conductivity layer.

[0013] In the photodetector according to the present invention, the high refractive index layer may have a structure in which the area of ​​the cross-section perpendicular to the optical axis of the lens gradually decreases in the direction from the lens toward the magnetic element.

[0014] This configuration allows the photodetector element of the present invention to efficiently arrange a high refractive index layer in the optical path from the light incident on the metalens until it reaches the magnetic element.

[0015] In the photodetector according to the present invention, the high refractive index layer may have a structure in which the area of ​​the cross-section perpendicular to the optical axis of the lens decreases in a stepwise manner from the lens toward the magnetic element.

[0016] This configuration allows the photodetector element of the present invention to efficiently arrange a high refractive index layer in the optical path from the light incident on the metalens to the magnetic element using a simple manufacturing process.

[0017] In the photodetector element according to the present invention, the high refractive index layer may further be configured such that the area of ​​the cross-section perpendicular to the optical axis of the lens gradually or in a stepwise manner decreases, and the area of ​​that portion is surrounded by the high thermal conductivity layer.

[0018] With this configuration, the photodetector element of the present invention can improve the heat dissipation of magnetic elements and the like, as the high refractive index layer is surrounded by a high thermal conductivity layer.

[0019] In the photosensing element according to the present invention, the high refractive index layer may be composed of at least one material selected from the group consisting of germanium, silicon, tantalum oxide, silicon nitride, titanium oxide, gallium oxide, hafnium oxide, niobium oxide, zinc sulfide, zirconium oxide, and cerium oxide.

[0020] Since the above materials have a high refractive index and can ensure the necessary light transmittance, they are suitable for the high refractive index layer of the photosensing element according to the present invention.

[0021] Also, in order to achieve the above object, the photosensing element according to the present invention includes a lens, a magnetic element including a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, an insulating layer provided so as to cover the periphery of the magnetic element, and a high refractive index layer having a higher refractive index than the insulating layer, and the light passing through the lens and the high refractive index layer is irradiated onto the magnetic element.

[0022] With this configuration, in the photosensing element of the present invention, by passing light through a high refractive index layer having a refractive index larger than that of the insulating layer, the spot of the light irradiated onto the magnetic element can be made smaller. By making the spot of the light smaller, the thermal energy generated by the light can be efficiently absorbed by the magnetic element, and the sensitivity of the photosensing element can be improved.

Effect of the Invention

[0023] According to the present invention, it is possible to provide a photosensing element that concentrates the irradiated light in a narrow region to suppress loss of light energy and perform efficient photosensing.

Brief Description of the Drawings

[0024] [Figure 1] It is a cross-sectional view showing the configuration of a photosensing element according to a first embodiment of the present invention. [Figure 2] It is a partially enlarged cross-sectional view showing the configuration of the magnetic element shown in FIG. 1. [Figure 3](a) is a diagram showing how light is focused by the lens shown in Figure 1, and (b) is a diagram showing how light is focused by the lens in a conventional photodetector. [Figure 4] This is a cross-sectional view showing the configuration of a photodetector element according to a second embodiment of the present invention. [Figure 5] Figure 4 is a plan view showing the configuration of the metalens. [Figure 6] This figure shows how light is focused by the metalens shown in Figure 4. [Figure 7] This is a cross-sectional view showing the configuration of a photodetector element according to a third embodiment of the present invention. [Figure 8] This is a cross-sectional view showing the configuration of a photodetector element according to a fourth embodiment of the present invention. [Figure 9] This is a cross-sectional view showing the configuration of a photodetector element according to a fifth embodiment of the present invention. [Figure 10] (a) is a plan view of Figure 9, and (b) is a cross-sectional view of Figure 9 along line AA. [Figure 11] This is a cross-sectional view showing the configuration of a photodetector element according to the sixth embodiment of the present invention. [Figure 12] (a) is a plan view of Figure 11, and (b) is a cross-sectional view of Figure 11 along line BB. [Figure 13] This is a cross-sectional view showing the configuration of a photodetector element according to the seventh embodiment of the present invention. [Figure 14] (a) is a plan view of Figure 13, and (b) is a cross-sectional view of Figure 13 along line CC. [Figure 15] This is a cross-sectional view showing the configuration of a photodetector element according to the eighth embodiment of the present invention. [Figure 16] (a) is a plan view of Figure 15, and (b) is a cross-sectional view of Figure 15 along line DD. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for ease of understanding, the scale of the parts in the drawings may differ from the actual scale. In the xyz Cartesian coordinate system set in the drawings, the x-axis and y-axis directions are horizontal, and the z-axis direction is vertical. The positive z-axis direction is also called the upward direction, and the negative z-axis direction is also called the downward direction, but this is unrelated to the direction of gravity. A degree of deviation is permissible in directions such as parallel, perpendicular, orthogonal, horizontal, vertical, up and down, and left and right, as long as it does not impair the effects of the embodiment. Furthermore, the "~" indicating a numerical range means that the values ​​written before and after it are included as the lower and upper limits, respectively.

[0026] [First Embodiment] First, a first embodiment of the present invention will be described.

[0027] (composition) Figure 1 is a cross-sectional view showing the configuration of a photodetector 101 according to a first embodiment of the present invention. As shown in Figure 1, the photodetector 101 has a lens 20 and a magnetic element 10, and a high refractive index layer 30 is provided between the lens 20 and the magnetic element 10. The high refractive index layer 30 has a higher refractive index than the lens 20. Light that has passed through the lens 20 and the high refractive index layer 30 is irradiated onto the magnetic element 10. The magnetic element 10 detects the light irradiated onto it. The magnetic element 10 converts the light irradiated onto it into an electrical signal. This electrical signal is extracted using a first electrode 11 and a second electrode 12 provided above and below the magnetic element 10. The lens 20 focuses the light toward the magnetic element 10. The magnetic element 10 is positioned, for example, at the focal point of the light focused by the lens 20. The photodetector 101 may be columnar, for example, prismatic, cylindrical, etc.

[0028] The term "light" as used herein is not limited to visible light, but may also include infrared radiation with a longer wavelength than visible light, or ultraviolet radiation with a shorter wavelength than visible light. The wavelength of visible light is, for example, 380 nm or more and less than 800 nm. The wavelength of infrared radiation is, for example, 800 nm or more and less than 1 mm. The wavelength of ultraviolet radiation is, for example, 200 nm or more and less than 380 nm.

[0029] The following describes each component.

[0030] (Magnetic element) Figure 2 is a partially enlarged cross-sectional view showing the configuration of the magnetic element 10 in Figure 1. As shown in Figure 2, the magnetic element 10 comprises at least a first ferromagnetic layer 1, a second ferromagnetic layer 2, and a spacer layer 3 sandwiched between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. In Figure 2, the second ferromagnetic layer 2, the spacer layer 3, the first ferromagnetic layer 1, and the cap layer 4 are stacked in this order in the positive z-axis direction to form a laminate 15. The laminate 15 constituting the magnetic element 10 may further include other layers such as a third ferromagnetic layer, a buffer layer, a seed layer, a magnetic coupling layer, and a perpendicular magnetization induction layer as needed.

[0031] As shown in Figures 1 and 2, a first electrode 11 is formed on the lens 20 side of the laminate 15, and a second electrode 12 is formed on the opposite side of the laminate 15 from the lens 20 via a cap layer 13. When referring to the magnetic element 10, it may include the first electrode 11, second electrode 12, cap layer 13, insulating layer 40, etc., in addition to the laminate 15. The cap layer 4 is located between the first ferromagnetic layer 1 and the first electrode 11, and the cap layer 13 is located between the second ferromagnetic layer 2 and the second electrode 12. The insulating layer 40 is located between the high refractive index layer 30 and the cap layer 13 or the second electrode 12, and is provided to cover the periphery of the laminate 15 and the first electrode 11.

[0032] The magnetic element 10 is, for example, an MTJ (Magnetic Tunnel Junction) element in which the spacer layer 3 is made of an insulating material. In this case, the magnetic element 10 can exhibit the tunnel magnetoresistance (TMR) effect. The resistance value of the magnetic element 10 changes when light is irradiated from the outside. The resistance value in the z-axis direction (resistance value when current is passed in the z-axis direction) of the magnetic element 10 changes in accordance with the relative change between the magnetization M1 state of the first ferromagnetic layer 1 and the magnetization M2 state of the second ferromagnetic layer 2. For example, the resistance value in the z-axis direction of the magnetic element 10 changes in accordance with the change in the relative angle between the direction of magnetization M1 of the first ferromagnetic layer 1 and the direction of magnetization M2 of the second ferromagnetic layer 2. Also, for example, the resistance value in the z-axis direction of the magnetic element 10 changes in accordance with the change in the magnitude of magnetization M1 of the first ferromagnetic layer 1.

[0033] Furthermore, for example, if the spacer layer 3 is made of metal, the magnetic element 10 can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element. Even when the magnetic element 10 is a GMR element, the resistance value in the z-axis direction (the resistance value when current is passed in the z-axis direction) changes according to the relative change between the magnetization M1 state of the first ferromagnetic layer 1 and the magnetization M2 state of the second ferromagnetic layer 2. Depending on the constituent material of the spacer layer 3, the magnetic element 10 may be called an MTJ element, a GMR element, etc., but it is collectively called a magnetoresistance effect element. The overall thickness of the magnetic element 10 is, for example, 15 nm to 40 nm.

[0034] The magnetic element 10 has to be a ferromagnetic material whose magnetization state changes upon irradiation with light, and whose resistance value changes in accordance with the change in magnetization state. For example, in addition to the MTJ element and GMR element described above, anisotropic magnetoresistance (AMR) effect element, colossal magnetoresistance (CMR) effect element, etc. can be used as the magnetic element 10.

[0035] The magnetic element 10 is positioned at the focal point of the light in the usable band focused by the lens 20. The focal point of the light in the usable band preferably overlaps with, for example, the first ferromagnetic layer 1. For example, when using visible light, the magnetic element 10 is positioned at the focal point of a specific wavelength range within the wavelength range of 380 nm to less than 800 nm. For example, when using infrared light, the magnetic element 10 is positioned at the focal point of a specific wavelength range within the wavelength range of 800 nm to 1 mm. For example, when using ultraviolet light, the magnetic element 10 is positioned at the focal point of a specific wavelength range within the wavelength range of 200 nm to less than 380 nm.

[0036] <First ferromagnetic layer> The first ferromagnetic layer 1 is a photosensitive layer whose magnetization state changes when light is irradiated from the outside. The first ferromagnetic layer 1 is also called the magnetization free layer. The magnetization free layer is a layer containing a magnetic material whose magnetization state changes when a predetermined external energy is applied. The predetermined external energy is, for example, light irradiated from the outside, a current flowing in the z-axis direction of the magnetic element 10, or an external magnetic field. The magnetization M1 of the first ferromagnetic layer 1 changes state according to the intensity of the irradiated light.

[0037] The first ferromagnetic layer 1 contains a ferromagnetic material. The first ferromagnetic layer 1 contains at least one of the magnetic elements such as Co, Fe, or Ni. The first ferromagnetic layer 1 may also contain elements such as B, Mg, Hf, and Gd along with the magnetic elements mentioned above. The first ferromagnetic layer 1 may be an alloy containing a magnetic element and a non-magnetic element, for example. The first ferromagnetic layer 1 may be composed of multiple layers. The first ferromagnetic layer 1 may be, for example, a CoFeB alloy, a laminate in which a CoFeB alloy layer is sandwiched between Fe layers, or a laminate in which a CoFeB alloy layer is sandwiched between CoFe layers. Generally, "ferromagnetism" includes "ferrimagnetism". The first ferromagnetic layer 1 may exhibit ferrimagnetism. Alternatively, the first ferromagnetic layer 1 may exhibit ferromagnetism that is not ferrimagnetism. For example, a CoFeB alloy exhibits ferromagnetism that is not ferrimagnetism.

[0038] The first ferromagnetic layer 1 may be an in-plane magnetized film having an easy magnetization axis in the direction within the film plane (any direction in the xy plane), or a perpendicular magnetized film having an easy magnetization axis in the direction perpendicular to the film plane (in the z-axis direction).

[0039] The thickness of the first ferromagnetic layer 1 is, for example, 1 nm to 5 nm. Preferably, the thickness of the first ferromagnetic layer 1 is, for example, 1 nm to 2 nm. When the first ferromagnetic layer 1 is a perpendicular magnetization film, if the thickness of the first ferromagnetic layer 1 is thin, the effect of perpendicular magnetic anisotropy applied from the layers above and below the first ferromagnetic layer 1 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 increases. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high, the force that causes the magnetization M1 to return to the z-axis direction is strengthened. On the other hand, if the thickness of the first ferromagnetic layer 1 is thick, the effect of perpendicular magnetic anisotropy applied from the layers above and below the first ferromagnetic layer 1 is relatively weakened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is weakened.

[0040] When the thickness of the first ferromagnetic layer 1 decreases, its volume as a ferromagnetic material decreases, and when its thickness increases, its volume as a ferromagnetic material increases. The reactivity of the magnetization of the first ferromagnetic layer 1 when external energy is applied is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and volume (V) of the first ferromagnetic layer 1. In other words, when the product of the magnetic anisotropy and volume of the first ferromagnetic layer 1 decreases, its reactivity to light increases. From this viewpoint, in order to increase the reactivity to light, it is preferable to appropriately design the magnetic anisotropy of the first ferromagnetic layer 1 and then reduce the volume of the first ferromagnetic layer 1.

[0041] If the thickness of the first ferromagnetic layer 1 is greater than 2 nm, an insertion layer made of, for example, Mo and W may be provided within the first ferromagnetic layer 1. That is, the first ferromagnetic layer 1 may be a laminate in which a ferromagnetic layer, an insertion layer, and a ferromagnetic layer are stacked in order in the z-axis direction. The interfacial magnetic anisotropy at the interface between the insertion layer and the ferromagnetic layer increases the perpendicular magnetic anisotropy of the entire first ferromagnetic layer 1. The thickness of the insertion layer is, for example, 0.1 nm to 1.0 nm.

[0042] <Second ferromagnetic layer> The second ferromagnetic layer 2 is a magnetization-fixed layer. The magnetization-fixed layer is a layer made of a magnetic material whose magnetization state changes less easily than that of the magnetization-free layer when a predetermined external energy is applied. For example, the magnetization direction of the magnetization-fixed layer changes less easily than that of the magnetization-free layer when a predetermined external energy is applied. Also, for example, the magnitude of magnetization of the magnetization-fixed layer changes less easily than that of the magnetization-free layer when a predetermined external energy is applied. The coercivity of the second ferromagnetic layer 2 is greater than that of the first ferromagnetic layer 1, for example. The second ferromagnetic layer 2 has an easy magnetization axis in the same direction as the first ferromagnetic layer 1, for example. The second ferromagnetic layer 2 may be an in-plane magnetized film or a perpendicular magnetized film.

[0043] The material constituting the second ferromagnetic layer 2 is, for example, the same as that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be a multilayer film in which Co with a thickness of 0.4 nm to 1.0 nm and Pt with a thickness of 0.4 nm to 1.0 nm are alternately stacked several times. The second ferromagnetic layer 2 may also be a laminate in which Co with a thickness of 0.4 nm to 1.0 nm, Mo with a thickness of 0.1 nm to 0.5 nm, a CoFeB alloy with a thickness of 0.3 nm to 1.0 nm, and Fe with a thickness of 0.3 nm to 1.0 nm are stacked in that order.

[0044] <Spacer layer> The spacer layer 3 is a layer placed between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The spacer layer 3 is composed of a conductor, an insulator, or a semiconductor, or a layer containing a current-carrying point composed of a conductor within an insulator. For example, the spacer layer 3 is a non-magnetic layer. The thickness of the spacer layer 3 can be adjusted according to the orientation direction of the magnetization of the first ferromagnetic layer 1 and the magnetization of the second ferromagnetic layer 2 in the initial state described later.

[0045] When the spacer layer 3 is composed of an insulating material, materials containing aluminum oxide, magnesium oxide, titanium oxide, or silicon oxide can be used as the material for the spacer layer 3. These insulating materials may also contain elements such as Al, B, Si, and Mg, or magnetic elements such as Co, Fe, and Ni. A high rate of change in magnetoresistance can be obtained by adjusting the film thickness of the spacer layer 3 so that a high TMR effect is exhibited between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. In order to efficiently utilize the TMR effect, the film thickness of the spacer layer 3 may be around 0.5 nm to 5.0 nm, or around 1.0 nm to 2.5 nm.

[0046] When the spacer layer 3 is made of a non-magnetic conductive material, conductive materials such as Cu, Ag, Au, or Ru can be used. In order to efficiently utilize the GMR effect, the film thickness of the spacer layer 3 may be around 0.5 nm to 5.0 nm, or around 2.0 nm to 3.0 nm.

[0047] When the spacer layer 3 is made of a non-magnetic semiconductor material, materials such as zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, or indium tin oxide (ITO) can be used. In this case, the film thickness of the spacer layer 3 may be approximately 1.0 nm to 4.0 nm.

[0048] When a layer containing current-carrying points composed of conductors in a non-magnetic insulator is applied as the spacer layer 3, the structure may include current-carrying points composed of non-magnetic conductors such as Cu, Au, and Al in a non-magnetic insulator composed of aluminum oxide or magnesium oxide. Alternatively, the conductors may be composed of magnetic elements such as Co, Fe, and Ni. In this case, the film thickness of the spacer layer 3 may be about 1.0 nm to 2.5 nm. The current-carrying points are, for example, columnar bodies with a diameter of 1 nm to 5 nm when viewed from a direction perpendicular to the film surface.

[0049] <Cap layer> The cap layer 4 is provided between the first ferromagnetic layer 1 and the first electrode 11. The cap layer 4 may include a perpendicular magnetization-inducing layer (not shown) that is laminated on the first ferromagnetic layer 1 and in contact with the first ferromagnetic layer 1. The cap layer 4 prevents damage to the underlying layer during the manufacturing process and enhances the crystallinity of the underlying layer during annealing. The thickness of the cap layer 4 is, for example, 10 nm or less, so that sufficient light is irradiated onto the first ferromagnetic layer 1.

[0050] <Insulating layer> The insulating layer 40 includes an insulating layer 41 filling the periphery of the laminate 15 and an insulating layer 42 filling the periphery of the first electrode 11. The insulating layer 41 and the insulating layer 42 are made of the same material, but may be different. The insulating layer 40 (insulating layer 41 and / or insulating layer 42) is, for example, an oxide, nitride, or oxynitride of Si, Al, or Mg. The insulating layer 40 (insulating layer 41 and / or insulating layer 42) is, for example, silicon dioxide (SiO₂). x ), silicon nitride (SiN x ), silicon carbide (SiC), chromium nitride, silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al2O3), zirconium oxide (ZrO3) x ) etc.

[0051] <1st electrode> The first electrode 11 is positioned, for example, on the lens 20 side of the magnetic element 10. Incident light is irradiated onto the magnetic element 10 from the side of the first electrode 11 and irradiates at least the first ferromagnetic layer 1. The first electrode 11 is made of a conductive material. The first electrode 11 is, for example, a transparent electrode that is transparent to light in the wavelength range used. Preferably, the first electrode 11 transmits 80% or more of the light in the wavelength range used. The first electrode 11 is, for example, an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). The first electrode 11 may have a configuration in which a plurality of columnar metals are contained within the transparent electrode material of these oxides.

[0052] It is not essential to use a transparent electrode material as the first electrode 11; a thin film of a metallic material such as Au, Cu, or Al may be used to allow the irradiated light to reach the first ferromagnetic layer 1. When a metal is used as the material for the first electrode 11, the film thickness of the first electrode 11 is, for example, 3 nm to 10 nm. The first electrode 11 may also have an anti-reflective coating on the irradiated surface to which the light is directed.

[0053] <Second electrode> The second electrode 12 is made of a conductive material. The second electrode 12 is made of a metal such as Cu, Al, or Au. Ta or Ti may be laminated above or below these metals. Alternatively, a laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN may be used. TiN or TaN may also be used as the second electrode 12. The film thickness of the second electrode 12 is, for example, 200 nm to 800 nm.

[0054] The second electrode 12 may be made transparent to light irradiated onto the magnetic element 10. As the material of the second electrode 12, similar to the first electrode 11, transparent electrode materials of oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), and indium gallium zinc oxide (IGZO) may be used. Even when light is irradiated from the first electrode 11, depending on the intensity of the light, the light may reach the second electrode 12. In this case, since the second electrode 12 is made of a transparent electrode material of oxide, the reflection of light at the interface between the second electrode 12 and the layer in contact with it can be suppressed compared to when the second electrode 12 is made of metal.

[0055] (High refractive index layer) The high refractive index layer 30 may be composed of at least one material selected from the group consisting of germanium, silicon, tantalum oxide, silicon nitride, titanium oxide, gallium oxide, hafnium oxide, niobium oxide, zinc sulfide, zirconium oxide, and cerium oxide. The high refractive index layer 30 has a refractive index greater than, for example, the lens 20. The high refractive index layer 30 has a refractive index greater than, for example, the insulating layer 40. The high refractive index layer 30 has a refractive index greater than, for example, the insulating layer 140 provided between the lens and the magnetic element in a conventional photodetector (see Figure 3(b)). The high refractive index layer 30 is, for example, a transparent layer that transmits light in the operating wavelength range. Preferably, the high refractive index layer 30 transmits 80% or more of the light in the operating wavelength range. The film thickness of the high refractive index layer 30, i.e., the thickness in the z-axis direction, is, for example, 100 nm to 1 mm.

[0056] (lens) The lens 20 is provided on the high refractive index layer 30 and is configured to focus the light incident on the lens 20 and irradiate the magnetic element 10. The lens 20 is, for example, a microlens. The lens 20 may be formed in the wafer process in which the photodetector element 101 is formed.

[0057] The light incident on lens 20 may be light that has passed through a polarizing filter. The photodetector element 101 may have a polarizing filter (not shown) on the side of lens 20 opposite to the magnetic element 10. If the light incident on photodetector element 101 is polarized light such as laser light, a polarizing filter is not necessary.

[0058] <Explanation of the principle> Figure 3(a) shows how light L is focused by the lens 20. Light L incident on the photodetector 101 is focused by the lens 20, forming a spot S of light at the focal length. In Figure 3(a), the spot S of light is formed on the first electrode 11, but the formation position of the spot S of light is not limited to this and may be on the first ferromagnetic layer 1. If the focusing angle of the lens 20 is θ and the refractive index of the high refractive index layer 30 is n, then the numerical aperture NA is NA = n·sinθ. If the wavelength of light is λ, then the spot diameter ω of the light is ω = k·λ / NA (where k is a constant). Therefore, even with the same lens diameter and focal length, the spot diameter ω of the focused light can be reduced by increasing the refractive index n of the high refractive index layer 30.

[0059] In contrast, Figure 3(b) shows how light is focused by a lens in a conventional photodetector. As shown in Figure 3(b), in a conventional photodetector, an insulating layer 140 is formed between the lens 20 and the magnetic element. The insulating layer 140 has a lower refractive index than the high refractive index layer 30 in Figure 3(a). Therefore, in the conventional photodetector shown in Figure 3(b), if the lens diameter and focal length are the same as in the first embodiment of the present invention, the spot diameter of the focused light becomes larger than the spot diameter of the first embodiment shown in Figure 3(a).

[0060] (Manufacturing process) The photodetector element 101 is obtained by sequentially fabricating the second electrode 12, the magnetic element 10, the first electrode 11, the high refractive index layer 30, and the lens 20.

[0061] The magnetic element 10 is manufactured by processes such as lamination, annealing, and processing of each layer. First, a cap layer 13, a second ferromagnetic layer 2, a spacer layer 3, a first ferromagnetic layer 1, and a cap layer 4 are laminated on the second electrode 12 in that order. Each layer is deposited, for example, by sputtering.

[0062] Next, the laminated film is annealed. The annealing temperature is, for example, 250°C to 400°C. After that, the laminated film is processed into a columnar laminate 15 by photolithography and etching (ion milling, etc.). The laminate 15, or each layer, may be mesa-shaped, cylindrical, prismatic, frustoconical, or truncated pyramidal. The shortest width of the laminate 15 when viewed from the z-axis direction is, for example, 10 nm to 1000 nm.

[0063] Next, an insulating layer 41 is formed to cover the sides of the laminate 15. The insulating layer 41 may be laminated multiple times. Next, the upper surface of the cap layer 4 is exposed from the insulating layer 41 by chemical mechanical polishing, and a first electrode layer is formed on the cap layer 4 and the insulating layer 41 by sputtering. The first electrode layer is processed into a columnar or plate-shaped first electrode 11, such as a cylindrical, prismatic, frustoconical, or pyramidal shape, by photolithography and etching. Next, an insulating layer 42 is embedded around the first electrode 11. Next, the upper surface of the first electrode 11 is exposed from the insulating layer 42 by chemical mechanical polishing, for example.

[0064] Next, a high refractive index layer 30 is formed on the first electrode 11 and the insulating layer 42. The high refractive index layer 30 may be laminated multiple times. Then, a lens 20 is placed on the high refractive index layer 30. The lens 20 is, for example, a microlens. A photodetector element 101 is obtained through the above steps. In this way, in the fabrication of the photodetector element 101, at least the magnetic element 10 to the high refractive index layer 30 can be formed continuously by a vacuum deposition process.

[0065] (Operation instructions) Next, the operation of the photodetector 101 according to the first embodiment will be described.

[0066] As shown in Figure 3(a), the light L incident on the photodetector 101 is focused by the lens 20, forming a light spot S at the focal point of the lens 20. The focal point of the lens 20 is located on the magnetic element 10, preferably the first ferromagnetic layer 1, but the focal point may also be located on the first electrode 11. That is, the light L that has passed through the lens 20 and the high refractive index layer 30 forms a light spot S and irradiates the magnetic element 10.

[0067] When the intensity of light irradiated onto the first ferromagnetic layer 1 changes, the state of magnetization M1 of the first ferromagnetic layer 1 changes. The state of magnetization M1 refers to, for example, the tilt angle of magnetization M1 with respect to the z-axis direction, the magnitude of magnetization M1, etc.

[0068] For example, when the intensity of light irradiated onto the first ferromagnetic layer 1 increases, the magnetization M1 of the first ferromagnetic layer 1 tilts from its initial state due to the external energy from the light irradiation. The angle between the direction of the magnetization M1 of the first ferromagnetic layer 1 when it is not irradiated with light and the direction of the magnetization M1 when it is irradiated with light is, for example, greater than 0° and less than 90°. Alternatively, for example, when the intensity of light irradiated onto the first ferromagnetic layer 1 increases, the magnitude of the magnetization M1 decreases.

[0069] When the magnetization M1 state of the first ferromagnetic layer 1 changes, the resistance value of the magnetic element 10 in the z-axis direction changes due to the magnetoresistance effect. When a constant current (sense current) is passed through the magnetic element 10 in the positive or negative z-axis direction using the first electrode 11 and the second electrode 12, an output voltage is obtained from the magnetic element 10. In other words, when the magnetization M1 state of the first ferromagnetic layer 1 changes, the output voltage from the magnetic element 10 also changes.

[0070] The intensity of light irradiated onto the first ferromagnetic layer 1 may take two values, for example, a first intensity and a second intensity. The first intensity may be zero when the intensity of light irradiated onto the first ferromagnetic layer 1 is zero. The intensity of light irradiated onto the first ferromagnetic layer 1 may also take multiple values, or it may change in an analog manner. If the intensity of the incident light takes multiple values, the output voltage of the magnetic element 10 may also take multiple values, and if the intensity of the light changes in an analog manner, the output voltage of the magnetic element 10 may also change in an analog manner. The photodetector element 101 can read out the differences in these output voltages (resistance values) as binary, multi-level, or analog data.

[0071] In the state in which the first ferromagnetic layer 1 is irradiated with light of a first intensity (referred to as the "initial state"), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 may be in a parallel or antiparallel relationship, and the magnetizations M1 and M2 may be orthogonal.

[0072] If magnetizations M1 and M2 are parallel in the initial state, a sense current is passed from the first ferromagnetic layer 1 towards the second ferromagnetic layer 2. By passing the sense current in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the same direction as the magnetization M2 of the second ferromagnetic layer 2, causing magnetizations M1 and M2 to be parallel in the initial state. Furthermore, by passing the sense current in this direction, it is possible to prevent the magnetization M1 of the first ferromagnetic layer 1 from reversing during operation.

[0073] If magnetizations M1 and M2 are antiparallel in the initial state, it is preferable to flow the sense current from the second ferromagnetic layer 2 towards the first ferromagnetic layer 1. By flowing the sense current in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the opposite direction to that of the magnetization M2 of the second ferromagnetic layer 2, causing magnetizations M1 and M2 to become antiparallel in the initial state.

[0074] When the intensity of the light irradiated onto the first ferromagnetic layer 1 returns to the first intensity, the spin transfer torque acts due to the sense current, or the magnetization M1 state of the first ferromagnetic layer 1 returns to its original state due to the action of magnetic anisotropy, and the magnetic element 10 returns to its initial state.

[0075] In this way, the photodetector 101 according to the first embodiment focuses the incident light L with the lens 20 and the high refractive index layer 30 to form a small-diameter light spot which irradiates the magnetic element 10, and converts the change in the intensity of the irradiated light into a change in the output voltage from the magnetic element 10. In other words, the photodetector 101 can convert light into an electrical signal.

[0076] As described above, in the first embodiment, the photodetector element 101 can reduce the spot size of light irradiated onto the magnetic element 10 by allowing light to pass through a high refractive index layer 30, which has a higher refractive index than the lens 20. By reducing the spot size of the light, the thermal energy generated by the light can be efficiently absorbed by the magnetic element 10, thereby improving the sensitivity of the photodetector element 101.

[0077] [Second Embodiment] Next, a second embodiment of the present invention will be described. Figure 4 is a cross-sectional view showing the configuration of a photodetector element 102 according to the second embodiment of the present invention. The second embodiment differs from the first embodiment in that the lens is a metalens 23. The other configurations are the same as in the first embodiment, and the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0078] (Metalens) Figure 5 is a plan view showing the configuration of the metalens 23 shown in Figure 4. As shown in Figure 5, the metalens 23 comprises a plurality of nanostructures 21 arranged two-dimensionally in the xy plane. The plurality of nanostructures 21 may be arranged on the base portion 22 in a predetermined arrangement pattern, for example, within a circular region R. The nanostructures 21 are, for example, cylinders, but may also be prisms, rectangular parallelepipeds, etc.

[0079] If the nanostructure 21 is cylindrical, the metalens 23 may contain multiple types of nanostructures 21 with different diameters of the circular top surface and cylindrical heights. If the nanostructure 21 is rectangular, the metalens 23 may vary the arrangement angle of the nanostructures 21 at their positions within region R. The arrangement angle is the angle that the longitudinal direction of the rectangular top surface of the nanostructure 21 makes with respect to the reference axis (e.g., the x-axis direction). The distribution of arrangement angles may have, for example, a regularity of Pancharatnam Berry geometric topology. The top surface size of the nanostructure 21 (diameter of the circular top surface in the case of a cylinder, length of the longitudinal direction and width of the transverse direction of the top rectangle in the case of a rectangular prism) and the spacing between adjacent nanostructures 21 are less than or equal to the wavelength of light used.

[0080] The area of ​​each of the multiple nanostructures 21 contained within the circular region R, viewed in a planar manner from the z-axis direction, may be varied, for example, according to the distance from the center of the circular region R. The area of ​​each of the multiple nanostructures 21 contained within the circular region R, viewed in a planar manner from the z-axis direction, may be made smaller, for example, as you move outward from the center of the circular region R.

[0081] The metalens 23 is a lens that utilizes a metasurface. The metalens 23 functions as a lens by controlling the phase distribution of light. A metasurface exhibits the functionality of a metamaterial through its planar structure. A metamaterial is a medium with a negative refractive index, or a medium designed to have a refractive index (dielectric constant, permeability) that does not exist in nature. Because the metalens 23 allows for a smaller focal length, the photodetector element 102 can be miniaturized.

[0082] The metalens 23 includes, for example, a dielectric that generates surface plasmon excitation. The metalens 23 also transmits light in the usable band. The metalens 23 may be composed of at least one material selected from the group consisting of, for example, tantalum oxide, silicon nitride, titanium oxide, gallium oxide, silicon oxide, and aluminum oxide. The film thickness of the metalens 23, i.e., the thickness in the z-axis direction, is, for example, 100 nm to 10 μm.

[0083] The metalens 23 can control the phase distribution of light by adjusting the arrangement of multiple nanostructures 21, the size of each nanostructure 21, and the period of the arrangement of the multiple nanostructures 21. Furthermore, by adjusting the size and period of the arrangement of the nanostructures 21, the focal length of the metalens 23 can be kept the same even if the wavelength of the incident light is different.

[0084] Figure 6 shows how light is focused by the metalens 23 shown in Figures 4 and 5. Light L incident on the photodetector element 102 is focused by the metalens 23, forming a spot S of light at the focal length. In Figure 6, the spot S of light is formed at the position of the first electrode 11, but the formation position of the spot S of light is not limited to this, and it may also be formed in the first ferromagnetic layer 1. Similar to Figure 3(a), if the focusing angle of the metalens 23 is θ and the refractive index of the high refractive index layer 30 is n, then the numerical aperture NA is NA = n·sinθ. If the wavelength of light is λ, then the spot diameter ω of the light is ω = k·λ / NA (where k is a constant). Therefore, even with metalens of the same lens diameter and focal length, the spot diameter ω of the focused light can be reduced by increasing the refractive index n of the high refractive index layer 30 placed between the metalens 23 and the magnetic element 10.

[0085] (Manufacturing process) The manufacturing process from the second electrode 12 to the high refractive index layer 30 is the same as in the first embodiment. In the second embodiment, a base portion 22 is formed on the upper surface of the high refractive index layer 30, a resist with a predetermined pattern formed by photolithography is formed on the upper surface of the base portion 22, and dry etching is performed. By dry etching, a plurality of nanostructures 21 with a predetermined pattern are formed on the upper surface of the base portion 22, thereby forming a metalens 23. Through the above steps, a photodetector element 102 is obtained. In this way, in the fabrication of the photodetector element 102, the magnetic element 10 to the metalens 23 can be formed continuously by a vacuum deposition process.

[0086] As described above, in the second embodiment, the photodetector element 102, similar to the first embodiment, allows light to pass through a high refractive index layer 30 with a higher refractive index than the metalens 23, thereby reducing the spot of light irradiated onto the magnetic element 10. This allows the thermal energy generated by the light to be efficiently absorbed by the magnetic element 10, improving the sensitivity of the photodetector element 102. Furthermore, in the second embodiment, the photodetector element 102 uses a metalens 23 comprising a plurality of two-dimensionally arranged nanostructures 21 as the lens, allowing the magnetic element 10 and the metalens 23 to be manufactured in a consistent manufacturing process. This simplifies the manufacturing process and enables the creation of a miniature lens suitable for the miniature magnetic element 10.

[0087] [Third Embodiment] A third embodiment of the present invention will now be described. Figure 7 is a cross-sectional view showing the configuration of a photodetector 103 according to the third embodiment of the present invention. The third embodiment differs from the second embodiment in that it includes a high thermal conductivity layer 50 between the metalens 23 and the magnetic element 10. The other configurations are the same as those of the second embodiment, and the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0088] (High thermal conductivity layer) The high thermal conductivity layer 50 is provided with a predetermined thickness between the metalens 23 and the magnetic element 10, and between the high refractive index layer 31 and the magnetic element 10. Specifically, the high thermal conductivity layer 50 and the high refractive index layer 31 are stacked in this order on the first electrode 11 and the insulating layer 40, and the metalens 23 is provided on the high refractive index layer 31. The high thermal conductivity layer 50 has a higher thermal conductivity than, for example, the high refractive index layer 31. The high thermal conductivity layer 50 may have a higher thermal conductivity than, for example, the insulating layer 40 and the first electrode 11, or both of them. The thermal conductivity of the high thermal conductivity layer 50 is, for example, greater than 40 W / m·K. A portion of the heat generated in the magnetic element 10 and the first electrode 11 is dissipated through the high thermal conductivity layer 50.

[0089] The high thermal conductivity layer 50 is, for example, an insulator. The high thermal conductivity layer 50 may be composed of at least one material selected from the group consisting of, for example, silicon carbide, aluminum nitride, and boron nitride.

[0090] The high thermal conductivity layer 50 may be, for example, a metal. The high thermal conductivity layer 50 may also be, for example, a non-magnetic material. If the high thermal conductivity layer 50 is a non-magnetic material, no leakage magnetic field will be generated from the high thermal conductivity layer 50, and the deterioration of the magnetic properties of the magnetic element 10 can be suppressed. The high thermal conductivity layer 50 may contain, for example, copper, gold, or silver.

[0091] The high thermal conductivity layer 50, whether an insulator or a metal, transmits light in the operating wavelength range. Preferably, the high thermal conductivity layer 50 transmits 80% or more of the light in the operating wavelength range.

[0092] As described above, the photodetector 103 according to the third embodiment can convert light into an electrical signal by replacing the light irradiated onto the magnetic element 10 with an output voltage from the magnetic element 10. Furthermore, the presence of a highly thermally conductive layer 50 with high thermal conductivity on the outside of the magnetic element 10, which generates heat when irradiated with light, promotes heat dissipation from the magnetic element 10 through the first electrode 11 or the insulating layer 40. In other words, when the irradiation of light to the first ferromagnetic layer 1 is stopped, the magnetic element 10 cools down quickly, and the recovery to the initial state of magnetization M1 is rapid. A faster return of the magnetization M1 of the first ferromagnetic layer 1 to the initial state improves the light response characteristics of the photodetector 103. In other words, the response of the photodetector 103 to light becomes faster.

[0093] (High refractive index layer) The material of the high refractive index layer 31 is the same as that of the high refractive index layer 30 in the first and second embodiments, and may include, for example, at least one material selected from the group consisting of germanium, silicon, tantalum oxide, silicon nitride, titanium oxide, gallium oxide, hafnium oxide, niobium oxide, zinc sulfide, zirconium oxide, and cerium oxide. The high refractive index layer 31 has a refractive index greater than, for example, the metalens 23. The high refractive index layer 31 has a refractive index greater than, for example, the insulating layer 40. The high refractive index layer 31 has a refractive index greater than, for example, the high thermal conductivity layer 50. The high refractive index layer 31 is, for example, a transparent layer that is transparent to light in the wavelength range used. Preferably, the high refractive index layer 31 transmits, for example, 80% or more of the light in the wavelength range used.

[0094] The thicknesses of the high refractive index layer 31 and the high thermal conductivity layer 50 can be set appropriately, taking into consideration light transmittance, light spot diameter, heat dissipation performance, etc.

[0095] (Manufacturing process) The manufacturing process from the second electrode 12 to the first electrode 11 and the insulating layer 42 is the same as in the first and second embodiments. In the third embodiment, a high thermal conductivity layer 50 and a high refractive index layer 31 are laminated in this order in the positive z-axis direction on the first electrode 11 and the insulating layer 42, and a metalens 23 is formed thereon in the manner described above. The high thermal conductivity layer 50 may be deposited by sputtering, for example, and may be laminated in multiple layers. The high refractive index layer 31 may be deposited by sputtering, for example, and may be laminated in multiple layers.

[0096] As described above, in the third embodiment, the photodetector element 103 can reduce the spot size of light irradiated onto the magnetic element 10 by allowing light to pass through the high refractive index layer 31, which has a higher refractive index than the metalens 23. This allows the magnetic element 10 to efficiently absorb the thermal energy generated by the light, thereby improving the sensitivity of the photodetector element 103. In addition, the photodetector element 103 of the third embodiment can improve the heat dissipation of the photodetector element 103 by including a high thermal conductivity layer 50, which has a higher thermal conductivity than the high refractive index layer 31.

[0097] [Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. Figure 8 is a cross-sectional view showing the configuration of a photodetector 104 according to the fourth embodiment of the present invention. In the fourth embodiment, the stacking order of the high refractive index layer 32 and the high thermal conductivity layer 51 provided between the metalens 23 and the magnetic element 10 in the z-axis positive direction differs from that of the third embodiment. The other configurations are the same as in the third embodiment, and the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0098] (High thermal conductivity layer) The high thermal conductivity layer 51 is provided between the metalens 23 and the magnetic element 10, specifically between the metalens 23 and the high refractive index layer 32. Specifically, the high refractive index layer 32 and the high thermal conductivity layer 51 are stacked in this order on the first electrode 11 and the insulating layer 42, and the metalens 23 is provided on the high thermal conductivity layer 51. The high thermal conductivity layer 51 has a higher thermal conductivity than, for example, the high refractive index layer 32. The high thermal conductivity layer 51 may have a higher thermal conductivity than, for example, the insulating layer 40 and the first electrode 11, or both. The high thermal conductivity layer 51 may have a higher thermal conductivity than, for example, the metalens 23. The thermal conductivity of the high thermal conductivity layer 51 is, for example, greater than 40 W / m·K. A portion of the heat generated in the magnetic element 10 and the first electrode 11 is dissipated from the high thermal conductivity layer 51 via the high refractive index layer 32.

[0099] The material of the high thermal conductivity layer 51 is the same as that of the high thermal conductivity layer 50 in the third embodiment. The high thermal conductivity layer 51 transmits light in the operating band.

[0100] Similar to the third embodiment, the photodetector 104 according to the fourth embodiment can convert light into an electrical signal by replacing the light irradiated onto the magnetic element 10 with an output voltage from the magnetic element 10. Furthermore, the presence of a high thermal conductivity layer 51 on the outside of the magnetic element 10, which generates heat when irradiated with light, allows for efficient dissipation of heat conducted from the magnetic element 10 to the high refractive index layer 32 via the first electrode 11 or the insulating layer 40. In other words, when the irradiation of light to the first ferromagnetic layer 1 is stopped, the magnetic element 10 cools down quickly, and the magnetization M1 recovers to its initial state quickly. A faster recovery of the magnetization M1 of the first ferromagnetic layer 1 to its initial state improves the light response characteristics of the photodetector 104. In other words, the response of the photodetector 104 to light becomes faster.

[0101] (High refractive index layer) The material of the high refractive index layer 32 is the same as that of the high refractive index layer 31 in the third embodiment. The high refractive index layer 32 has a refractive index greater than, for example, the metalens 23. The high refractive index layer 32 has a refractive index greater than, for example, the insulating layer 40. The high refractive index layer 32 has a refractive index greater than, for example, the high thermal conductivity layer 51. The high refractive index layer 32 is, for example, a transparent layer that transmits light in the wavelength range used. Preferably, the high refractive index layer 32 transmits 80% or more of the light in the wavelength range used.

[0102] The thicknesses of the high refractive index layer 32 and the high thermal conductivity layer 51 can be set appropriately, taking into consideration factors such as light transmittance, light spot diameter, and heat dissipation performance.

[0103] (Manufacturing process) The manufacturing process from the second electrode 12 to the first electrode 11 and the insulating layer 42 is the same as in the first to third embodiments. In the fourth embodiment, a high refractive index layer 32 and a high thermal conductivity layer 51 are laminated in this order in the positive z-axis direction on the first electrode 11 and the insulating layer 42, and a metalens 23 is formed thereon in the manner described above. The high refractive index layer 32 may be deposited by sputtering, for example, and may be laminated in multiple layers. The high thermal conductivity layer 51 may be deposited by sputtering, for example, and may be laminated in multiple layers.

[0104] As described above, in the fourth embodiment, the photodetector element 104 can reduce the spot size of light irradiated onto the magnetic element 10 by allowing light to pass through a high refractive index layer 32 which has a higher refractive index than the metalens 23. This allows the magnetic element 10 to efficiently absorb the thermal energy generated by the light, thereby improving the sensitivity of the photodetector element 104. In addition, the photodetector element 104 of the fourth embodiment can improve the heat dissipation of the photodetector element 104 by including a high thermal conductivity layer 51 which has a higher thermal conductivity than the high refractive index layer 32.

[0105] [Fifth Embodiment] Next, a fifth embodiment of the present invention will be described. Figure 9 is a cross-sectional view showing the configuration of a photodetector element 105 according to the fifth embodiment of the present invention. The fifth embodiment differs from the second embodiment in the shape of the high refractive index layer 33, etc. Other components are the same as in the second embodiment, and the same components are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0106] (composition) Figure 10(a) is a plan view of Figure 9, and Figure 10(b) is a cross-sectional view taken along line AA of Figure 9. As can be seen from Figures 9 and 10, the high refractive index layer 33 has a structure in which the area of ​​the cross-section perpendicular to the optical axis OA of the metalens 23 gradually decreases from the metalens 23 toward the magnetic element 10. The high refractive index layer 33 is, for example, a frustoconical shape tapering downward (negative z-axis direction), but it may also be a frustoconical shape, cone shape, pyramidal shape, etc. In the case of a frustoconical shape, the high refractive index layer 33 has an upper and lower surface perpendicular to the z-axis direction and inclined sides as its outer surfaces. The upper surface of the high refractive index layer 33 is provided in contact with the lower surface of the metalens 23 and is sized to encompass the region R in Figure 10(a). The lower surface of the high refractive index layer 33 is provided in contact with the upper surface of the first electrode 11. Preferably, the high refractive index layer 33 is provided so as to encompass at least the optical path OP (see Figure 6) through which light travels from the metalens 23 to the first electrode 11. The size of the lower surface of the high refractive index layer 33 may be set so as to encompass at least the region in which the entire optical path intersects the upper surface of the first electrode 11 when a light spot is formed at the first electrode 11 or the first ferromagnetic layer 1.

[0107] (High refractive index layer) The material of the high refractive index layer 33 is the same as that of the high refractive index layer 30 in the first embodiment. The high refractive index layer 33 has a refractive index greater than, for example, the metalens 23. The high refractive index layer 33 has a refractive index greater than, for example, the insulating layer 40 or insulating layer 43. The high refractive index layer 33 is, for example, a transparent layer that is transparent to light in the wavelength range used. It is preferable that the high refractive index layer 33 transmits, for example, 80% or more of the light in the wavelength range used. The film thickness of the high refractive index layer 33, i.e., the thickness in the z-axis direction, is, for example, 100 nm to 1 mm.

[0108] (Insulating layer) The high refractive index layer 33 is surrounded by an insulating layer 43 around the portion of the metalens 23 where the area of ​​the cross-section perpendicular to the optical axis OA gradually decreases, i.e., the side surface of the frustoconical portion. The material of the insulating layer 43 is the same as, but may be different from, the insulating layer 41 or 42 that constitute the insulating layer 40.

[0109] (Manufacturing process) The manufacturing process from the second electrode 12 to the first electrode 11 and the insulating layer 42 is the same as in the first to fourth embodiments. In the fifth embodiment, a high refractive index layer 33, for example, in the shape of a frustoconical form, is formed on the first electrode 11 and the insulating layer 42, and an insulating layer 43 is formed to fill the periphery of the high refractive index layer 33. A metalens 23 is formed on the upper surface of the high refractive index layer 33 in the manner described above.

[0110] The high refractive index layer 33 and the insulating layer 43 may be formed by, for example, depositing a high refractive index layer film on the first electrode 11 and the insulating layer 42 by sputtering, forming a frustoconical high refractive index layer 33 by photolithography and etching, and then filling the periphery of the high refractive index layer 33 with the insulating layer 43. If necessary, the upper surfaces of the high refractive index layer 33 and the insulating layer 43 may be flattened by, for example, chemical mechanical polishing. The high refractive index layer 33 and the insulating layer 43 may also be formed in a laminated manner by repeating the above process while gradually increasing the size of the frustoconical portion.

[0111] Alternatively, the high refractive index layer 33 and the insulating layer 43 may be formed by, for example, depositing an insulating layer film on the first electrode 11 and the insulating layer 42 by sputtering, forming a frustoconical through-hole in the center of the upper surface of the insulating layer film by photolithography or etching, and forming the high refractive index layer 33 in the formed through-hole. If necessary, the upper surfaces of the high refractive index layer 33 and the insulating layer 43 may be flattened by, for example, chemical mechanical polishing. The high refractive index layer 33 and the insulating layer 43 may also be formed in a laminated manner by repeating the above process while gradually increasing the size of the through-hole.

[0112] As described above, in the fifth embodiment, the photodetector element 105 can reduce the spot size of light irradiated onto the magnetic element 10 by allowing light to pass through a high refractive index layer 33, which has a higher refractive index than the metalens 23. This allows the magnetic element 10 to efficiently absorb the thermal energy generated by the light, thereby improving the sensitivity of the photodetector element 105. Furthermore, in the fifth embodiment, the photodetector element 105 can efficiently arrange the high refractive index layer 33 in the optical path OP from the metalens 23 to the magnetic element 10 or the first electrode 11.

[0113] [Sixth Embodiment] Next, a sixth embodiment of the present invention will be described. Figure 11 is a cross-sectional view showing the configuration of a photodetector 106 according to the sixth embodiment of the present invention. In the sixth embodiment, the shapes of the high refractive index layer 34 and the insulating layer 44 differ from those of the fifth embodiment. The other configurations are the same as in the fifth embodiment, and the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0114] (composition) Figure 12(a) is a plan view of Figure 11, and Figure 12(b) is a cross-sectional view of Figure 11 along line BB. As can be seen from Figures 11 and 12, the high refractive index layer 34 has a structure in which the area of ​​the cross-section perpendicular to the optical axis OA of the metalens 23 decreases in a stepped manner from the metalens 23 toward the magnetic element 10. For example, the high refractive index layer 34 is formed in a stepped manner on all or part of the side surface of the frustoconical high refractive index layer 33 of the fifth embodiment. The upper surface of the high refractive index layer 34 is provided in contact with the lower surface of the metalens 23 and is sized to at least encompass the region R in Figure 12(a). The lower surface of the high refractive index layer 34 is provided in contact with the upper surface of the first electrode 11. Preferably, the high refractive index layer 34 is provided to at least encompass the entire optical path OP through which light travels from the metalens 23 to the first electrode 11. The size of the lower surface of the high refractive index layer 34 may be set, for example, to include at least the region where the optical path OP intersects with the upper surface of the first electrode 11 when the light spot is formed on the first electrode 11 or the first ferromagnetic layer 1.

[0115] (High refractive index layer) The material of the high refractive index layer 34 is the same as that of the high refractive index layer 33 in the fifth embodiment. The high refractive index layer 34 has a refractive index greater than, for example, the metalens 23. The high refractive index layer 34 has a refractive index greater than, for example, the insulating layer 40 or insulating layer 44. The high refractive index layer 34 is, for example, a transparent layer that is transparent to light in the wavelength range used. Preferably, the high refractive index layer 34 transmits, for example, 80% or more of the light in the wavelength range used. The film thickness of the high refractive index layer 34, i.e., the thickness in the z-axis direction, is, for example, 100 nm to 1 mm.

[0116] (Insulating layer) The high refractive index layer 34 is surrounded by an insulating layer 44 around the portion where the area of ​​the cross-section perpendicular to the optical axis OA of the metalens 23 decreases in a stepped manner. The insulating layer 44 is a layer in which annular insulating layers 45, 46, 47, 48, 49, each with a circular through-hole formed in the center, are stacked in this order in the positive z-axis direction. The number of annular insulating layers (number of steps) constituting the insulating layer 44 is not limited to 5, and any number can be used. The diameter of the central circular through-hole of the annular insulating layers 45, 46, 47, 48, 49 increases in this order so that the high refractive index layer 34 covers at least the entire optical path OP from the metalens 23 to the first electrode 11. The thickness of each annular insulating layer 45, 46, 47, 48, 49 is the same, but may be partially or entirely different. The material of insulating layers 45, 46, 47, 48, 49 is the same as that of insulating layer 41 or 42, but may be different. The materials of the insulating layers 45, 46, 47, 48, and 49 are all the same, but some or all of them may be different.

[0117] (Manufacturing process) The manufacturing process from the second electrode 12 to the first electrode 11 and the insulating layer 42 is the same as in the first to fifth embodiments. In the sixth embodiment, a high refractive index layer 34 with stepped sides and an insulating layer 44 filling the periphery of the high refractive index layer 34 are formed on the first electrode 11 and the insulating layer 42. A metalens 23 is formed on the upper surface of the high refractive index layer 34 in the manner described above.

[0118] Specifically, a high refractive index layer film of a predetermined thickness is deposited on the first electrode 11 and the insulating layer 42, for example by sputtering. The bottom cylindrical portion of the high refractive index layer 34 is then formed to a predetermined thickness by photolithography and etching, and the area around the bottom cylindrical portion of the formed high refractive index layer 33 is filled with the insulating layer 45. If necessary, the upper surfaces of the insulating layer 45 and the bottom cylindrical portion of the high refractive index layer 34 may be flattened by, for example, chemical mechanical polishing. The high refractive index layer 34 and the insulating layer 44 are formed by repeating the above process up to the insulating layer 49 while gradually increasing the size of the cylindrical portion of the high refractive index layer 34.

[0119] Alternatively, an insulating layer film of a predetermined thickness may be formed on the first electrode 11 and the insulating layer 42, for example by sputtering, and a circular through-hole may be formed in the center of the insulating layer film by photolithography or etching. The lowest layer of the high refractive index layer 34 may then be formed in the formed circular through-hole so that it is at the same level as the upper surface of the insulating layer 45. If necessary, the upper surfaces of the insulating layer 45 and the lowest layer of the high refractive index layer 34 may be flattened by, for example, chemical mechanical polishing. The high refractive index layer 34 and the insulating layer 44 are formed by repeating the above process up to the insulating layer 49 while gradually increasing the size of the through-hole. A high refractive index layer film of a predetermined thickness may then be formed on top of the insulating layer 49.

[0120] As described above, in the sixth embodiment, the photodetector element 106 can reduce the spot size of light irradiated onto the magnetic element 10 by allowing light to pass through a high refractive index layer 34, which has a higher refractive index than the metalens 23. This allows the magnetic element 10 to efficiently absorb the thermal energy generated by the light, thereby improving the sensitivity of the photodetector element 106. Furthermore, in the sixth embodiment, the photodetector element 106 can efficiently arrange the high refractive index layer 34 in the optical path OP from the metalens 23 to the magnetic element 10 or the first electrode 11 using a simple manufacturing process.

[0121] [Seventh Embodiment] Next, a seventh embodiment of the present invention will be described. Figure 13 is a cross-sectional view showing the configuration of a photodetector 107 according to the seventh embodiment of the present invention. The seventh embodiment differs from the fifth embodiment in that it has a high thermal conductivity refill layer 52. The other configurations are the same as those of the fifth embodiment, and the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0122] (composition) Figure 14(a) is a plan view of Figure 13, and Figure 14(b) is a cross-sectional view of Figure 13 along line CC. As can be seen from Figures 13 and 14, the high refractive index layer 33 has a structure in which the area of ​​the cross-section perpendicular to the optical axis OA of the metalens 23 gradually decreases from the metalens 23 toward the magnetic element 10. The high refractive index layer 33 is, for example, a frustoconical shape tapering downward (negative z-axis direction), but it may also be a frustoconical shape, a cone shape, a pyramidal shape, etc. In the case of a frustoconical shape, the high refractive index layer 33 has an upper and lower surface perpendicular to the z-axis direction and inclined sides as its outer surfaces. The upper surface of the high refractive index layer 33 is provided in contact with the lower surface of the metalens 23 and is large enough to encompass at least the region R in Figure 14(a). The lower surface of the high refractive index layer 33 is provided in contact with the upper surface of the first electrode 11. Preferably, the high refractive index layer 33 is provided so as to encompass at least the entire optical path OP through which light travels from the metalens 23 to the first electrode 11. The size of the lower surface of the high refractive index layer 33 may be set so as to encompass at least the region where the optical path OP intersects with the upper surface of the first electrode 11 when a light spot is formed at the first electrode 11 or the first ferromagnetic layer 1.

[0123] (High refractive index layer) The material of the high refractive index layer 33 is the same as that of the high refractive index layer 33 in the fifth embodiment. The high refractive index layer 33 has a refractive index greater than, for example, the metalens 23. The high refractive index layer 33 has a refractive index greater than, for example, the insulating layer 40. The high refractive index layer 33 has a refractive index greater than, for example, the high thermal conductivity refill layer 52. The high refractive index layer 33 is, for example, a transparent layer that is transparent to light in the wavelength range used. It is preferable that the high refractive index layer 33 transmits, for example, 80% or more of the light in the wavelength range used. The film thickness of the high refractive index layer 33, i.e., the thickness in the z-axis direction, is, for example, 100 nm to 1 mm.

[0124] (High thermal conductivity refill layer) The high refractive index layer 33 is surrounded by a high thermal conductivity refill layer 52 as a high thermal conductivity layer on the sides of the frustoconical portion, i.e., the portion where the area of ​​the cross-section perpendicular to the optical axis OA of the metalens 23 gradually decreases. The material of the high thermal conductivity refill layer 52 may be the same as or different from the high thermal conductivity layer 50 of the third embodiment and the high thermal conductivity layer 51 of the fourth embodiment. The high thermal conductivity refill layer 52 does not need to be light-transmitting. The lower surface of the high thermal conductivity refill layer 52 may be in contact with at least a portion of the upper surface of the first electrode 11. The lower surface of the high thermal conductivity refill layer 52 may be in contact with at least a portion of the upper surface of the insulating layer 42.

[0125] The photodetector 107 according to the seventh embodiment can convert light into an electrical signal by replacing the light irradiated onto the magnetic element 10 with an output voltage from the magnetic element 10. Furthermore, the presence of a highly thermally conductive refill layer 52 on the outside of the magnetic element 10, which generates heat when irradiated with light, promotes heat dissipation from the magnetic element 10 through the first electrode 11 or the insulating layer 40. In addition, heat transferred from the magnetic element 10 to the high refractive index layer 33 via the first electrode 11 can be dissipated through the highly thermally conductive refill layer 52. In other words, when the irradiation of light to the first ferromagnetic layer 1 is stopped, the magnetic element 10 cools down quickly, and the recovery to the initial state of magnetization M1 is rapid. A faster return of the magnetization M1 of the first ferromagnetic layer 1 to the initial state improves the light response characteristics of the photodetector 107. In other words, the response of the photodetector 107 to light becomes faster.

[0126] (Manufacturing process) The manufacturing process from the second electrode 12 to the first electrode 11 and the insulating layer 42 is the same as in the first to sixth embodiments. In the seventh embodiment, a high refractive index layer 33, for example, in the shape of a frustoconical pyramid, and a high thermal conductivity refill layer 52 filling the periphery of the high refractive index layer 33 are formed on the first electrode 11 and the insulating layer 42. A metalens 23 is formed on the upper surface of the high refractive index layer 33 in the manner described above.

[0127] Specifically, the high refractive index layer 33 and the high thermal conductivity refill layer 52 may be formed by, for example, depositing a high refractive index layer film on the first electrode 11 and the insulating layer 42 by sputtering, forming a frustoconical high refractive index layer 33 by photolithography and etching, and filling the periphery of the high refractive index layer 33 with the high thermal conductivity refill layer 52. If necessary, the upper surfaces of the high refractive index layer 33 and the high thermal conductivity refill layer 52 may be flattened by, for example, chemical mechanical polishing. The high refractive index layer 33 and the high thermal conductivity refill layer 52 may also be formed in a laminated manner by repeating the above process while gradually increasing the size of the frustoconical portion.

[0128] Alternatively, the high refractive index layer 33 and the high thermal conductivity refill layer 52 may be formed by, for example, depositing a high thermal conductivity refill layer film on the first electrode 11 and the insulating layer 42 by sputtering, forming a frustoconical through-hole in the center of the high thermal conductivity refill film by photolithography or etching, and forming the high refractive index layer 33 in the formed through-hole. If necessary, the upper surfaces of the high refractive index layer 33 and the high thermal conductivity refill layer 52 may be flattened by, for example, chemical mechanical polishing. The high refractive index layer 33 and the high thermal conductivity refill layer 52 may also be formed in a laminated manner by repeating the above process while gradually increasing the size of the through-hole.

[0129] As described above, in the seventh embodiment, the photodetector element 107 can reduce the spot size of light irradiated onto the magnetic element 10 by allowing light to pass through a high refractive index layer 33, which has a higher refractive index than the metalens 23. This allows the magnetic element 10 to efficiently absorb the thermal energy generated by the light, thereby improving the sensitivity of the photodetector element 107. Furthermore, in the seventh embodiment, the photodetector element 107 can efficiently arrange the high refractive index layer 33 in the optical path OP from the metalens 23 to the magnetic element 10 or the first electrode 11. In addition, in the seventh embodiment, the photodetector element 107 can improve the heat dissipation of the photodetector element 107, including the magnetic element 10, by having the high refractive index layer 33 surrounded by a high thermal conductivity refill layer 52.

[0130] [Eighth Embodiment] An eighth embodiment of the present invention will now be described. Figure 15 is a cross-sectional view showing the configuration of a photodetector 108 according to the eighth embodiment of the present invention. The eighth embodiment differs from the sixth embodiment in that it has a high thermal conductivity refill layer 53. The other configurations are the same as those of the sixth embodiment, and the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0131] (composition) Figure 16(a) is a plan view of Figure 15, and Figure 16(b) is a cross-sectional view of Figure 15 along line DD. As can be seen from Figures 15 and 16, the high refractive index layer 34 has a structure in which the area of ​​the cross section perpendicular to the optical axis OA of the metalens 23 decreases in a stepped manner from the metalens 23 toward the magnetic element 10. For example, the high refractive index layer 34 is formed in a stepped manner on all or part of the side surface of the frustoconical high refractive index layer 33 of the seventh embodiment. The upper surface of the high refractive index layer 34 is provided in contact with the lower surface of the metalens 23 and is sized to at least encompass the region R in Figure 16(a). The lower surface of the high refractive index layer 34 is provided in contact with the upper surface of the first electrode 11. Preferably, the high refractive index layer 34 is provided to at least encompass the entire optical path OP through which light travels from the metalens 23 to the first electrode 11. The size of the lower surface of the high refractive index layer 34 may be set, for example, to include at least the region where the optical path OP intersects with the upper surface of the first electrode 11 when the light spot is formed on the first electrode 11 or the first ferromagnetic layer 1.

[0132] (High refractive index layer) The material of the high refractive index layer 34 is the same as that of the high refractive index layer 34 in the sixth embodiment. The high refractive index layer 34 has a refractive index greater than, for example, the metalens 23. The high refractive index layer 34 has a refractive index greater than, for example, the high thermal conductivity refill layer 53. The high refractive index layer 34 is, for example, a transparent layer that transmits light in the wavelength range used. Preferably, the high refractive index layer 34 transmits 80% or more of the light in the wavelength range used. The film thickness of the high refractive index layer 34, i.e., the thickness in the z-axis direction, is, for example, 100 nm to 1 mm.

[0133] (High thermal conductivity refill layer) The high refractive index layer 34 is surrounded by a high thermal conductivity refill layer 53 around the portion where the area of ​​the cross-section perpendicular to the optical axis OA of the metalens 23 decreases in a stepped manner. The high thermal conductivity refill layer 53 is a layer in which annular high thermal conductivity layers 54, 55, 56, 57, 58, 59, each with a circular through-hole in the center, are stacked in this order in the positive z-axis direction. The number of high thermal conductivity layers (number of stages) constituting the high thermal conductivity refill layer 53 is not limited to 6, and any number can be used. The annular high thermal conductivity layer 54 is formed to surround the first electrode 11. The annular high thermal conductivity layers 55, 56, 57, 58, 59 have a gradual increase in the diameter of the central circular through-hole in this order, so that the high refractive index layer 34 at least encompasses the entire optical path OP from the metalens 23 to the first electrode 11. The thickness of each high thermal conductivity layer 54, 55, 56, 57, 58, 59 may be the same, or some or all of them may be different. The material of each high thermal conductivity layer 54, 55, 56, 57, 58, 59 is the same as that of the high thermal conductivity layer 50 in the third embodiment, the high thermal conductivity layer 51 in the fourth embodiment, or the high thermal conductivity refill layer 52 in the seventh embodiment. The material of each high thermal conductivity layer 54, 55, 56, 57, 58, 59 may all be the same, or some or all of them may be different.

[0134] (Manufacturing process) The manufacturing process from the second electrode 12 to the magnetic element 10 and the insulating layer 41 is the same as in the first to seventh embodiments. In the eighth embodiment, the first electrode 11 and a high thermal conductivity layer 54 or insulating layer are formed on the magnetic element 10 and the insulating layer 41, and a high refractive index layer 34 and a high thermal conductivity refill layer 53 filling the periphery of the high refractive index layer 34 are formed thereon. A metalens 23 is formed on the upper surface of the high refractive index layer 34 in the manner described above.

[0135] Specifically, a high refractive index layer film of a predetermined thickness is deposited on the first electrode 11 and the high thermal conductivity layer 54, for example by sputtering. The bottom cylindrical portion of the high refractive index layer 34 is formed by, for example, photolithography or etching, and the area around the formed cylindrical portion of the high thermal conductivity layer 33 is filled with the high thermal conductivity layer 55. If necessary, the top surfaces of the high thermal conductivity layer 55 and the bottom cylindrical portion of the high thermal conductivity layer 34 may be flattened by, for example, chemical mechanical polishing. By repeating the above process up to the high thermal conductivity layer 59 while gradually increasing the size of this cylindrical portion, the high refractive index layer 34 and the high thermal conductivity refill layer 53 can be formed in a stacked manner.

[0136] Alternatively, a high thermal conductivity layer film of a predetermined thickness can be deposited on the first electrode 11 and the high thermal conductivity layer 54, for example by sputtering, and a circular through-hole can be formed in the center of the high thermal conductivity layer film by photolithography or etching. The bottom cylindrical portion of the high refractive index layer 34 can then be formed in the formed through-hole. If necessary, the top surfaces of the high thermal conductivity layer 55 and the bottom cylindrical portion of the high refractive index layer 34 may be flattened by, for example, chemical mechanical polishing. By repeating the above process up to the high thermal conductivity layer 59 while gradually increasing the size of the through-hole, the high refractive index layer 34 and the high thermal conductivity refill layer 53 can be formed in a laminated manner.

[0137] As described above, in the eighth embodiment of the photodetector element 108, the light passes through a high refractive index layer 34 which has a higher refractive index than the metalens 23, thereby reducing the spot of light irradiated onto the magnetic element 10. This allows the magnetic element 10 to efficiently absorb the thermal energy generated by the light, thereby improving the sensitivity of the photodetector element 107. Furthermore, in the eighth embodiment of the photodetector element 108, the high refractive index layer 34 can be efficiently arranged in the optical path OP from the metalens 23 to the magnetic element 10 or the first electrode 11 using a simple manufacturing process. In addition, in the eighth embodiment of the photodetector element 108, the high refractive index layer 34 is surrounded by a high thermal conductivity refill layer 53, which improves the heat dissipation of the photodetector element 108, including the magnetic element 10.

[0138] [Examples of application] The photodetectors 101 to 108 of the first to eighth embodiments can be applied to optical sensors such as image sensors in which a plurality of photodetectors are arranged in one or two dimensions. Such optical sensors can be used in information terminal devices such as smartphones, tablets, personal computers, and digital cameras.

[0139] Furthermore, the photodetectors 101 to 108 of the first to eighth embodiments can be applied, for example, to the photoelectric conversion elements of receiving devices in a communication system where multiple transmitting and receiving devices are connected by optical fibers, and the receiving devices transmit and receive optical signals such as laser light. The above communication system may be a communication system that performs short- and medium-distance communication, such as within and between data centers, or long-distance communication, such as between cities. The transmitting and receiving devices are installed, for example, within a data center.

[0140] Furthermore, the above communication system may be, for example, a communication system that wirelessly transmits and receives optical signals, such as near-infrared light, between mobile terminals such as smartphones and tablets. Alternatively, the above communication system may be, for example, a communication system that wirelessly transmits and receives optical signals, such as near-infrared light, between a mobile terminal and an information processing device such as a personal computer.

[0141] The present invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

[0142] As described above, the present invention has the effect of concentrating irradiated light into a narrow area to suppress the loss of light energy and enable efficient light detection, and is useful for light detection elements in general. [Explanation of Symbols]

[0143] 1 First ferromagnetic layer 2 Second ferromagnetic layer 3 Spacer layer 4, 13 cap layer 10 Magnetic elements 11 1st electrode 12 Second electrode 15 Laminate 20 lenses 21 Nanostructures 22 Base section 23 Metalens 30, 31, 32, 33, 34 High refractive index layer 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 140 Insulating layer 50, 51, 54, 55, 56, 57, 58, 59 High thermal conductivity layer 52, 53 High thermal conductivity refill layer 101, 102, 103, 104, 105, 106, 107, 108 Photodetector M1, M2 magnetization OA optical axis OP optical path R region S Light Spot

Claims

1. Lens and, A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, A high refractive index layer having a refractive index greater than that of the lens is provided between the lens and the magnetic element, A photodetector comprising the lens and the high refractive index layer, wherein light that has passed through the lens and the high refractive index layer is irradiated onto the magnetic element.

2. The photodetector element according to claim 1, wherein the lens is a metalens comprising a plurality of nanostructures arranged in two dimensions.

3. The photodetector according to claim 2, further comprising a high thermal conductivity layer having a higher thermal conductivity than the high refractive index layer between the lens and the magnetic element.

4. The photodetector element according to claim 3, wherein the high refractive index layer has a structure in which the area of ​​the cross-section perpendicular to the optical axis of the lens gradually decreases in the direction from the lens toward the magnetic element.

5. The photodetector element according to claim 3, wherein the high refractive index layer has a structure in which the area of ​​the cross-section perpendicular to the optical axis of the lens decreases in a stepwise manner from the lens toward the magnetic element.

6. Furthermore, the high refractive index layer is surrounded by the high thermal conductivity layer around the portion where the area of ​​the cross-section perpendicular to the optical axis of the lens gradually or in a stepwise manner decreases. This is the photodetector element according to claim 4 or 5.

7. The photodetector element according to claim 6, wherein the high refractive index layer is composed of at least one material selected from the group consisting of germanium, silicon, tantalum oxide, silicon nitride, titanium oxide, gallium oxide, hafnium oxide, niobium oxide, zinc sulfide, zirconium oxide, and cerium oxide.

8. Lens and, A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, An insulating layer is provided so as to cover the periphery of the magnetic element, A high refractive index layer having a higher refractive index than the aforementioned insulating layer, A photodetector comprising the lens and the high refractive index layer, wherein light that has passed through the lens and the high refractive index layer is irradiated onto the magnetic element.

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