Patent Publication Number: US-2022231181-A1

Title: Photodetection element, receiving device, and optical sensor device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Priority is claimed on Japanese Patent Application No. 2021-005590, filed Jan. 18, 2021 and Japanese Patent Application No. 2021-167503, filed Oct. 12, 2021, the content of which is incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a photodetection element, a receiving device, and an optical sensor device. 
     Photoelectric conversion elements are used for various purposes. 
     For example, Patent Document 1 describes a receiving device that receives an optical signal using a photodiode. The photodiode is, for example, a pn junction diode using a semiconductor pn junction or the like, and converts light into an electrical signal. 
     For example, in Patent Document 2, an optical sensor using a semiconductor pn junction and an image sensor using the optical sensor are disclosed. 
     PATENT DOCUMENTS 
     [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2001-292107 
     [Patent Document 2] U.S. Pat. No. 9,842,874 
     SUMMARY 
     Although photodetection elements using semiconductor pn junctions are widely used, new photodetection elements are required for further development. Also, a photodetection element often generates heat that adversely affects an element and a circuit when light is applied and improvement in heat dissipation is required. 
     It is desirable to provide a photodetection element, a receiving device, and an optical sensor device having excellent heat dissipation. 
     The following means is provided. 
     According to a first aspect, there is provided a photodetection element including: a magnetic element including a first ferromagnetic layer to which light is applied, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; a first electrode in contact with a first surface of the magnetic element, the first surface being located on a first ferromagnetic layer side of the magnetic element in a lamination direction; a second electrode in contact with a second surface of the magnetic element, the second surface being opposite to the first surface; and a first high thermal conductivity layer disposed outside of the first ferromagnetic layer and having higher thermal conductivity than the first electrode. 
     According to a second aspect, there is provided a photodetection element including: a magnetic element including a first ferromagnetic layer to which light is applied, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; and a first high thermal conductivity layer disposed outside of the first ferromagnetic layer and being a nonmagnetic metal. 
     According to a third aspect, there is provided a receiving device including: the photodetection element according to the above-described aspect. 
     According to a fourth aspect, there is provided an optical sensor device including: the photodetection element according to the above-described aspect. 
     The photodetection element, the receiving device, and the optical sensor device according to the above-described aspects have excellent heat dissipation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a photodetection element according to a first embodiment. 
         FIG. 2  is a diagram for describing a first mechanism of a first operation example of the photodetection element according to the first embodiment. 
         FIG. 3  is a diagram for describing a second mechanism of the first operation example of the photodetection element according to the first embodiment. 
         FIG. 4  is a diagram for describing a first mechanism of a second operation example of the photodetection element according to the first embodiment. 
         FIG. 5  is a diagram for describing a second mechanism of the second operation example of the photodetection element according to the first embodiment. 
         FIG. 6  is a cross-sectional view of a photodetection element according to a first modified example. 
         FIG. 7  is a cross-sectional view of a photodetection element according to a second modified example. 
         FIG. 8  is a cross-sectional view of a photodetection element according to a third modified example. 
         FIG. 9  is a cross-sectional view of a photodetection element according to a fourth modified example. 
         FIG. 10  is a cross-sectional view of a photodetection element according to a fifth modified example. 
         FIG. 11  is a cross-sectional view of a photodetection element according to a sixth modified example. 
         FIG. 12  is a cross-sectional view of a photodetection element according to a seventh modified example. 
         FIG. 13  is a block diagram of a transceiver device according to a first application example. 
         FIG. 14  is a conceptual diagram of an example of a communication system. 
         FIG. 15  is a conceptual diagram of a cross-section of an optical sensor device according to a second application example. 
         FIG. 16  is a schematic view of an example of a terminal device. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, featured parts may be enlarged parts for convenience so that the features of the present disclosure are easier to understand, and dimensional ratios and the like of the respective components may be different from actual ones. Materials, dimensions, and the like exemplified in the following description are examples, the present disclosure is not limited thereto, and modifications can be appropriately made in a range in which advantageous effects of the present disclosure are exhibited. 
     Directions will be defined. A lamination direction of a magnetic element  10  is defined as a z direction, one direction within a plane orthogonal to the z direction is defined as an x direction, and a direction orthogonal to the x direction and the z direction is defined as a y direction. The z direction is an example of the lamination direction. Hereinafter, a +z direction may be expressed as an “upward” direction and a −z direction may be expressed as a “downward” direction. The +z direction is a direction from a second ferromagnetic layer 2 to a first ferromagnetic layer 1. The upward and downward directions do not always coincide with a direction in which gravity is applied. 
       FIG. 1  is a cross-sectional view of a photodetection element  100  according to the first embodiment. The photodetection element  100  replaces a change in a state of applied light with an electrical signal. A resistance value of the photodetection element  100  in the z direction changes with the state of the applied light. An output voltage from the photodetection element  100  changes with the state of the applied light. The light in the present specification is not limited to visible light and also includes infrared light having a wavelength longer than that of the visible light and ultraviolet light having a wavelength shorter than that of the visible light. The wavelength of the visible light is, for example, 380 nm or more and less than 800 nm. The wavelength of the infrared light is, for example, 800 nm or more and 1 mm or less. The wavelength of the ultraviolet light is, for example, 200 nm or more and less than 380 nm. 
     The photodetection element  100  includes, for example, the magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  20 , an insulating layer  30 , and a substrate  40 . 
     The magnetic element  10  has, for example, the first ferromagnetic layer 1, the second ferromagnetic layer 2, a spacer layer 3, and a cap layer 4. The spacer layer 3 is located between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The cap layer 4 covers an upper surface of the magnetic element  10  in the lamination direction. The cap layer 4 is, for example, on the first ferromagnetic layer 1. The magnetic element  10  may have other layers in addition to these. 
     The magnetic element  10  is, for example, a magnetic tunnel junction (MTJ) element in which the spacer layer 3 is made of an insulating material. In this case, in the magnetic element  10 , a resistance value in the z direction (a resistance value when a current flows in the z direction) changes in accordance with a relative change between a state of magnetization of the first ferromagnetic layer 1 and a state of magnetization of the second ferromagnetic layer 2. Such an element is also called a magnetoresistance effect element. 
     The first ferromagnetic layer 1 is a photodetection layer whose magnetization state changes when light is applied thereto from the outside. The first ferromagnetic layer 1 is also called a magnetization free layer. The magnetization free layer is a layer including a magnet whose magnetization state changes when a prescribed external force has been applied. The prescribed external force is, for example, light which is applied from the outside, a current flowing in the z direction of the magnetic element  10 , or an external magnetic field. The state of the magnetization of the first ferromagnetic layer 1 changes with an intensity of light that is applied to the first ferromagnetic layer 1. 
     The first ferromagnetic layer 1 includes a ferromagnet. The first ferromagnetic layer 1 includes at least one of magnetic elements such as Co, Fe, and Ni. The first ferromagnetic layer 1 may include nonmagnetic elements such as B, Mg, Hf, and Gd in addition to the above-described magnetic elements. The first ferromagnetic layer 1 may be, for example, an alloy including a magnetic element and a nonmagnetic element. The first ferromagnetic layer 1 may include a plurality of layers. The first ferromagnetic layer 1 is, for example, a CoFeB alloy, a laminate in which a CoFeB alloy layer is sandwiched between Fe layers, and a laminate in which a CoFeB alloy layer is sandwiched between CoFe layers. 
     The first ferromagnetic layer 1 may be an in-plane magnetization film having an axis of easy magnetization in a direction within a film surface (any direction within the xy plane) or may be a perpendicular magnetization film having an axis of easy magnetization in a direction (the z direction) perpendicular to the film surface. 
     A thickness of the first ferromagnetic layer 1 is, for example, 1 nm or more and 5 nm or less. The thickness of the first ferromagnetic layer 1 may be, for example, 1 nm or more and 2 nm or less. If the thickness of the first ferromagnetic layer 1 is thin when the first ferromagnetic layer 1 is a perpendicular magnetization film, the effect of applying perpendicular magnetic anisotropy from the layers above and below the first ferromagnetic layer 1 is strengthened and perpendicular magnetic anisotropy of the first ferromagnetic layer 1 increases. That is, when the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high, a force for the magnetization M 1  to return in the z direction is strengthened. On the other hand, when the thickness of the first ferromagnetic layer 1 is thick, the effect of applying the perpendicular magnetic anisotropy 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. 
     The volume of a ferromagnet becomes small when the thickness of the first ferromagnetic layer 1 becomes thin. The volume of a ferromagnet becomes large when the thickness of the first ferromagnetic layer 1 becomes thick. The susceptibility of the magnetization of the first ferromagnetic layer 1 when external energy has been applied is inversely proportional to a product (KuV) of the magnetic anisotropy (Ku) and the volume (V) of the first ferromagnetic layer 1. That is, when the product of the magnetic anisotropy and the volume of the first ferromagnetic layer 1 becomes small, the reactivity to light increases. From this point of view, the magnetic anisotropy of the first ferromagnetic layer 1 may be appropriately designed and then the volume of the first ferromagnetic layer 1 may be reduced so that the reaction to light increases. 
     When the thickness of the first ferromagnetic layer 1 is thicker 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 the ferromagnetic layer, the insertion layer, and the ferromagnetic layer are laminated in that order in the z direction. Interfacial magnetic anisotropy at an interface between the insertion layer and the ferromagnetic layer enhances the perpendicular magnetic anisotropy of the entire first ferromagnetic layer 1. A thickness of the insertion layer is, for example, 0.1 nm to 0.6 nm. 
     The second ferromagnetic layer 2 is a magnetization fixed layer. The magnetization fixed layer is a layer made of a magnet whose magnetization state is less likely to change than that of the magnetization free layer when prescribed external energy has been applied. For example, in the magnetization fixed layer, a direction of magnetization is less likely to change than that in the magnetization free layer when prescribed external energy has been applied. Also, for example, in the magnetization fixed layer, a magnitude of magnetization is less likely to change than that in the magnetization free layer when prescribed external energy is applied. For example, coercivity of the second ferromagnetic layer 2 is greater than that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 has an axis of easy magnetization in the same direction as the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be either an in-plane magnetization film or a perpendicular magnetization film. 
     For example, the material constituting the second ferromagnetic layer 2 is similar to that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be, for example, a laminate in which Co having a thickness of 0.4 nm to 1.0 nm, Mo having a thickness of 0.1 nm to 0.5 nm, a CoFeB alloy having a thickness of 0.3 nm to 1.0 nm, and Fe having a thickness of 0.3 nm to 1.0 nm are laminated in that order. 
     The magnetization of the second ferromagnetic layer 2 may be fixed by, for example, magnetic coupling to the third ferromagnetic layer via a magnetic coupling layer. In this case, a combination of the second ferromagnetic layer 2, the magnetic coupling layer, and the third ferromagnetic layer may be called a magnetization fixed layer. 
     The third ferromagnetic layer is magnetically coupled to, for example, the second ferromagnetic layer 2. The magnetic coupling is, for example, antiferromagnetic coupling and is caused by Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. The material constituting the third ferromagnetic layer is, for example, similar to that of the first ferromagnetic layer 1. The magnetic coupling layer is, for example, Ru, Ir, or the like. 
     The spacer layer 3 is a nonmagnetic layer arranged between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The spacer layer 3 includes a layer made of a conductor, an insulator, or a semiconductor or a layer including a current carrying point formed of a conductor within an insulator. A thickness of the spacer layer 3 can be adjusted in accordance with orientation directions of the magnetization of the first ferromagnetic layer 1 and the magnetization of the second ferromagnetic layer 2 in an initial state to be described below. 
     For example, when the spacer layer 3 is made of an insulator, the magnetic element  10  has a magnetic tunnel junction (MTJ) including the first ferromagnetic layer 1, the spacer layer 3, and the second ferromagnetic layer 2. Such an element is called an MTJ element. In this case, the magnetic element  10  can exhibit a tunnel magnetoresistance (TMR) effect. For example, when the spacer layer 3 is made of a metal, the magnetic element  10  can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element. The magnetic element  10  may be called the MTJ element, the GMR element, or the like, which differs according to the constituent material of the spacer layer 3, but they may also be collectively called magnetoresistance effect elements. 
     When the spacer layer 3 is made of an insulating material, materials including aluminum oxide, magnesium oxide, titanium oxide, silicon oxide, and the like can be used. Also, these insulating materials may include elements such as Al, B, Si, and Mg and magnetic elements such as Co, Fe, and Ni. A high magnetoresistance change rate can be obtained by adjusting the thickness of the spacer layer 3 so that a strong TMR effect is exhibited between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. In order to use the TMR effect efficiently, the thickness of the spacer layer 3 may be about 0.5 to 5.0 nm or about 1.0 to 2.5 nm. 
     When the spacer layer 3 is made of a nonmagnetic conductive material, a conductive material such as Cu, Ag, Au, or Ru can be used. In order to use the GMR effect efficiently, the thickness of the spacer layer 3 may be about 0.5 to 5.0 nm or about 2.0 to 3.0 nm. 
     When the spacer layer 3 is made of a nonmagnetic semiconductor material, a material such as zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, or indium tin oxide (ITO) can be used. In this case, the thickness of the spacer layer 3 may be about 1.0 to 4.0 nm. 
     When a layer including a current carrying point made of a conductor within a nonmagnetic insulator is applied as the spacer layer 3, a structure may be formed to include a current carrying point made of a nonmagnetic conductor of Cu, Au, Al, or the like within the nonmagnetic insulator made of aluminum oxide or magnesium oxide. Also, the conductor may be made of a magnetic element such as Co, Fe, or Ni. In this case, the thickness of the spacer layer 3 may be about 1.0 to 2.5 nm. The current carrying point is, for example, a columnar body having a diameter of 1 nm or more and 5 nm or less when viewed from a direction perpendicular to a film surface. 
     The cap layer 4 is between the first ferromagnetic layer 1 and the first electrode  11 . The cap layer 4 prevents damage to the lower layer during the process and enhances the crystallinity of the lower layer during annealing. The thickness of the cap layer 4 is, for example, 3 nm or less so that sufficient light is applied to the first ferromagnetic layer 1. The cap layer 4 is, for example, MgO, W, Mo, Ru, Ta, Cu, Cr, or a laminated film thereof. 
     The magnetic element  10  may also have a base layer, a perpendicular magnetization inducing layer, and the like. The base layer is between the second ferromagnetic layer 2 and the second electrode  12 . The base layer is a seed layer or a buffer layer. The seed layer enhances the crystallinity of the layer laminated on the seed layer. The seed layer is, for example, Pt, Ru, Hf, Zr, or NiFeCr. A thickness of the seed layer is, for example, 1 nm or more and 5 nm or less. The buffer layer is a layer that alleviates lattice mismatch between different crystals. The buffer layer is, for example, Ta, Ti, W, Zr, Hf, or a nitride of these elements. A thickness of the buffer layer is, for example, 1 nm or more and 5 nm or less. 
     A perpendicular magnetization inducing layer is formed when the first ferromagnetic layer 1 is a perpendicular magnetization film. The perpendicular magnetization inducing layer is laminated on the first ferromagnetic layer 1. The perpendicular magnetization inducing layer induces perpendicular magnetic anisotropy of the first ferromagnetic layer 1. The perpendicular magnetization inducing layer is, for example, magnesium oxide, W, Ta, Mo, or the like. When the perpendicular magnetization inducing layer is magnesium oxide, magnesium oxide may be oxygen-deficient to increase conductivity. A thickness of the perpendicular magnetization inducing layer is, for example, 0.5 nm or more and 2.0 nm or less. 
     The first electrode  11  is in contact with a first surface of the magnetic element  10 . The first surface is a surface of the magnetic element  10  on a side of the first ferromagnetic layer 1 (a first ferromagnetic layer side) in the z direction. The first electrode  11  has, for example, transparency with respect to a wavelength range of the light applied to the magnetic element  10 . 
     The first electrode  11  includes, for example, an oxide having transparency with respect the wavelength range of the light applied to the magnetic element  10 . The first electrode  11  is a transparent electrode including a transparent electrode material of 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 be configured to have a plurality of columnar metals in these transparent electrode materials. In this case, a film thickness of the first electrode  11  is, for example, 10 nm to 300 nm. It is not essential to use the above-described transparent electrode material as the first electrode  11  and light from the outside may be allowed to reach the first ferromagnetic layer 1 using a metallic material such as Au, Cu, or Al with a thin film thickness. When a metal is used as the material of the first electrode  11 , the film thickness of the first electrode  11  is, for example, 3 to 10 nm. In particular, Au has higher transmittance for light having a wavelength near a blue wavelength of light than other metallic materials. Also, the first electrode  11  may have an antireflection film on an irradiation surface to which light is applied. 
     The second electrode  12  is made of a conductive material. The second electrode  12  is made of, for example, metals such as Cu, Al, Au, and Ru. Ta and/or Ti may be laminated on the top and bottom of the above metals. Also, a laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, and a laminated film of Ta, Cu, and TaN may be used. Also, TiN and/or TaN may be used as the second electrode  12 . A film thickness of the second electrode  12  is for example, 200 nm to 800 nm. 
     The second electrode  12  may be made transparent to light applied to the magnetic element  10 . As the material of the second electrode  12 , as in the first electrode  11 , for example, a transparent electrode material of an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO) may be used. Even if light is applied from the first electrode  11 , the light may reach the second electrode  12  according to the intensity of the light. In this case, the second electrode  12  is configured to include a transparent electrode material of an oxide, so that the reflection of light at an interface between the second electrode  12  and a layer in contact with the second electrode  12  can be limited as compared with the case where the second electrode  12  is made of a metal. 
     The first high thermal conductivity layer  20  is located outside of the first ferromagnetic layer 1 when viewed from the z direction. The first high thermal conductivity layer  20  is located, for example, outside of the magnetic element  10  in the in-plane direction and covers at least a part of a sidewall of the magnetic element  10 . The first high thermal conductivity layer  20  is connected to the magnetic element  10  via, for example, the insulating layer  30 . The first high thermal conductivity layer  20  surrounds, for example, the circumference of at least a part of the magnetic element  10 . For example, the first high thermal conductivity layer  20  surrounds the circumference of the first ferromagnetic layer 1 of the magnetic element  10 . The first high thermal conductivity layer  20  is in contact with, for example, the first electrode  11 . When the first high thermal conductivity layer  20  and the first electrode  11  come into contact with each other, a heat path from the first high thermal conductivity layer  20  to the wiring via the first electrode  11  is formed and heat can be efficiently dissipated from the magnetic element  10 . 
     The first high thermal conductivity layer  20  has higher thermal conductivity than the first electrode  11 . The first high thermal conductivity layer  20  has higher thermal conductivity than, for example, the insulating layer  30 . The thermal conductivity of the first high thermal conductivity layer  20  is, for example, greater than 40 W/m·K. A part of the heat generated by the magnetic element  10  is dissipated via the first high thermal conductivity layer  20 . 
     The first high thermal conductivity layer  20  is, for example, a metal. The first high thermal conductivity layer  20  is, for example, nonmagnetic. If the first high thermal conductivity layer  20  is nonmagnetic, no leakage magnetic field is generated from the first high thermal conductivity layer  20  and it is possible to limit deterioration of the magnetic characteristics of the magnetic element  10 . When the first high thermal conductivity layer  20  is a nonmagnetic metal, for example, even if the first electrode  11  is a metal and the first electrode  11  has a higher thermal conductivity than the first high thermal conductivity layer  20 , the first high thermal conductivity layer  20  has high thermal conductivity. Thus, even if the first electrode  11  has higher thermal conductivity than the first high thermal conductivity layer  20 , heat can be efficiently dissipated from the magnetic element  10 . The first high thermal conductivity layer  20  includes, for example, copper, gold, or silver. 
     The first high thermal conductivity layer  20  may be an insulator. When the first high thermal conductivity layer  20  is made of an insulator, the first high thermal conductivity layer  20  includes, for example, silicon carbide, aluminum nitride, or boron nitride. 
     The insulating layer  30  is located between the magnetic element  10  and the first high thermal conductivity layer  20 . The insulating layer  30  covers, for example, the circumference of the magnetic element  10 . The insulating layer  30  is, for example, an oxide of Si, Al, or Mg, a nitride, or an oxynitride. The insulating layer  30  is, for example, silicon oxide (SiO x ), silicon nitride (SiN x ), silicon carbide (SiC), chromium nitride, silicon nitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al 2 O 3 ), and zirconium oxide (ZrO x ), or the like. 
     The photodetection element  100  is manufactured by a laminating process, an annealing process, and a processing process on each layer. First, the second electrode  12 , the second ferromagnetic layer 2, the spacer layer 3, the first ferromagnetic layer 1, and the cap layer 4 are laminated on the substrate in that order. Each layer is formed by, for example, sputtering. 
     Subsequently, the laminated film is annealed. An annealing temperature is, for example, 250° C. to 450° C. When the substrate is a circuit board, the laminated film may be annealed at 400° C. or higher. Subsequently, the laminated film is processed into a prescribed columnar body by photolithography and etching. The columnar body may be a cylindrical body or a prismatic body. For example, the shortest width when the columnar body is viewed from the z direction may be 10 nm or more and 2000 nm or less or 30 nm or more and 500 nm or less. 
     Subsequently, the insulating layer  30  is formed to cover the side surface of the columnar body. The insulating layer  30  may be laminated a plurality of times. Subsequently, the first high thermal conductivity layer  20  is formed on the insulating layer  30 . Subsequently, the upper surface of the cap layer 4 is exposed from the insulating layer  30  and the first high thermal conductivity layer  20  by chemical mechanical polishing (CMP) and the first electrode  11  is manufactured on the cap layer 4. In the above-described process, the photodetection element  100  is obtained. 
     Next, some examples of the operation of the photodetection element  100  will be described. Light whose intensity changes is applied to the first ferromagnetic layer 1. An output voltage from the photodetection element  100  changes when light is applied to the first ferromagnetic layer 1. In the first operation example, the case where the intensities of the light applied to the first ferromagnetic layer 1 are two levels of a first intensity and a second intensity will be described. The intensity of light of the second intensity is set to be greater than the intensity of light of the first intensity. The first intensity may correspond to the case where the intensity of light applied to the first ferromagnetic layer 1 is zero. 
       FIGS. 2 and 3  are diagrams for describing a first operation example of the photodetection element  100  according to the first embodiment.  FIG. 2  is a diagram for describing a first mechanism of the first operation example and  FIG. 3  is a diagram for describing a second mechanism of the first operation example. In the upper graphs of  FIGS. 2 and 3 , the vertical axis represents an intensity of light applied to the first ferromagnetic layer 1 and the horizontal axis represents time. In the lower graphs of  FIGS. 2 and 3 , the vertical axis represents a resistance value of the magnetic element  10  in the z direction and the horizontal axis represents time. 
     First, in a state in which light of the first intensity is applied to the first ferromagnetic layer 1 (hereinafter called an initial state), magnetization M 1  of the first ferromagnetic layer 1 is parallel to magnetization M 2  of the second ferromagnetic layer 2 and a resistance value of the magnetic element  10  in the z direction is a first resistance value R 1 , and a magnitude of an output voltage from the magnetic element  10  indicates a first value. The resistance value of the magnetic element  10  in the z direction is obtained by causing a sense current Is to flow through the magnetic element  10  in the z direction to generate a voltage across both ends of the magnetic element  10  in the z direction and using Ohm&#39;s law from a voltage value. An output voltage from the magnetic element  10  is generated between the first electrode  11  and the second electrode  12 . In the case of the example shown in  FIG. 2 , the sense current Is flows in a direction from the first ferromagnetic layer 1 to the second ferromagnetic layer 2. By causing the sense current Is to flow in the above direction, spin transfer torque in a direction, which is the same as that of the magnetization M 2  of the second ferromagnetic layer 2, acts on the magnetization M 1  of the first ferromagnetic layer 1, and the magnetization M 1  becomes parallel to the magnetization M 2  in the initial state. Also, by causing the sense current Is to flow in the above direction, it is possible to prevent the magnetization M 1  of the first ferromagnetic layer 1 from being inverted during operation. 
     Next, the intensity of the light applied to the first ferromagnetic layer 1 changes from the first intensity to the second intensity. The second intensity is greater than the first intensity and the magnetization M 1  of the first ferromagnetic layer 1 changes from the initial state. The state of the magnetization M 1  of the first ferromagnetic layer 1 in the state in which no light is applied to the first ferromagnetic layer 1 is different from the state of the magnetization M 1  of the first ferromagnetic layer 1 in the second intensity. The state of the magnetization M 1  is, for example, a tilt angle with respect to the z direction, a magnitude, or the like. 
     For example, as shown in  FIG. 2 , when the intensity of the light applied to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnetization M 1  is tilted in the z direction. Also, for example, as shown in  FIG. 3 , when the intensity of the light applied to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnitude of the magnetization M 1  becomes small. For example, when the magnetization M 1  of the first ferromagnetic layer 1 is tilted in the z direction due to an irradiation intensity of light, a tilt angle thereof is larger than 0° and smaller than 90°. 
     When the magnetization M 1  of the first ferromagnetic layer 1 changes from the initial state, the resistance value of the magnetoresistance effect element  10  in the z direction is a second resistance value R 2  and a magnitude of the output voltage from the magnetic element  10  is a second value. The second resistance value R 2  is larger than the first resistance value R 1  and the second value of the output voltage is larger than the first value. The second resistance value R 2  is between the resistance value (the first resistance value R 1 ) when the magnetization M 1  and the magnetization M 2  are parallel and the resistance value when the magnetization M 1  and the magnetization M 2  are antiparallel. 
     In the case shown in  FIG. 2 , spin transfer torque in a direction, which is the same as that of the magnetization M 2  of the second ferromagnetic layer 2, acts on the magnetization M 1  of the first ferromagnetic layer 1. Therefore, the magnetization M 1  tries to return to a state in which the magnetization M 1  is parallel to the magnetization M 2  and the magnetic element  10  returns to the initial state when the intensity of the light applied to the first ferromagnetic layer 1 changes from the second intensity to the first intensity. In the case shown in  FIG. 3 , when the intensity of the light applied to the first ferromagnetic layer 1 returns to the first intensity, the magnitude of the magnetization M 1  of the first ferromagnetic layer 1 returns to the original magnitude and the magnetic element  10  returns to the initial state. In either case, the resistance value of the magnetic element  10  in the z direction returns to the first resistance value R 1 . That is, when the intensity of the light applied to the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the resistance value of the photodetection element  100  in the z direction changes from the second resistance value R 2  to the first resistance value R 1 . 
     The output voltage from the photodetection element  100  changes in correspondence with a change in the intensity of the light applied to the first ferromagnetic layer 1 and the change in the intensity of the applied light can be transformed into a change in the output voltage from the photodetection element  100 . That is, the photodetection element  100  can replace the light with an electrical signal. For example, the case where the output voltage from the photodetection element  100  is greater than or equal to a threshold value is treated as a first signal (for example, “1”) and the case where the output voltage is less than the threshold value is treated as a second signal (for example, “0”). 
     Although the case where the magnetization M 1  is parallel to the magnetization M 2  in the initial state has been described as an example here, the magnetization M 1  may be antiparallel to the magnetization M 2  in the initial state. In this case, the resistance value of the magnetic element  10  in the z direction decreases as the state of the magnetization M 1  changes (for example, as the change in the angle of the magnetization M 1  increases from the initial state). When the initial state is the case where the magnetization M 1  is antiparallel to the magnetization M 2 , the sense current may flow in a direction from the second ferromagnetic layer 2 to the first ferromagnetic layer 1. By causing the sense current to flow in the above direction, spin transfer torque in a direction opposite to that of the magnetization M 2  of the second ferromagnetic layer 2 acts on the magnetization M 1  of the first ferromagnetic layer 1 and the magnetization M 1  becomes antiparallel to the magnetization M 2  in the initial state. 
     In the first operation example, the case where the light applied to the first ferromagnetic layer 1 has two levels of the first intensity and the second intensity has been described as an example, but in the second operation example, the case where the intensity of the light applied to the first ferromagnetic layer 1 changes at multiple levels or in an analog manner will be described. 
       FIGS. 4 and 5  are diagrams for describing a second operation example of the photodetection element  100  according to the first embodiment.  FIG. 4  is a diagram for describing a first mechanism of the first operation example and  FIG. 5  is a diagram for describing a second mechanism of the first operation example. In the upper graphs of  FIGS. 4 and 5 , the vertical axis represents an intensity of light applied to the first ferromagnetic layer 1 and the horizontal axis represents time. In the lower graphs of  FIGS. 4 and 5 , the vertical axis represents a resistance value of the magnetic element  10  in the z direction and the horizontal axis represents time. 
     In the case of  FIG. 4 , when the intensity of the light applied to the first ferromagnetic layer 1 changes, the magnetization M 1  of the first ferromagnetic layer 1 is tilted from the initial state due to external energy generated by the application of the light. An angle between the direction of the magnetization M 1  of the first ferromagnetic layer 1 when no light is applied to the first ferromagnetic layer 1 and the direction of the magnetization M 1  when light is applied to the first ferromagnetic layer 1 is greater than 0° and less than 90°. 
     When the magnetization M 1  of the first ferromagnetic layer 1 is tilted from the initial state, the resistance value of the magnetoresistance effect element  10  in the z direction changes. The output voltage from the magnetic element  10  changes. For example, the resistance value of the magnetic element  10  in the z direction changes to a second resistance value R 2 , a third resistance value R 3 , and a fourth resistance value R 4  in accordance with the tilt of the magnetization M 1  of the first ferromagnetic layer 1 and the output voltage from the magnetic element  10  changes to a second value, a third value, and a fourth value. The resistance value increases in the order of the first resistance value R 1 , the second resistance value R 2 , the third resistance value R 3 , and the fourth resistance value R 4 . The output voltage from the magnetic element  10  increases in the order of the first value, the second value, the third value, and the fourth value. 
     In the magnetic element  10 , when the intensity of the light applied to the first ferromagnetic layer 1 has changed, the output voltage from the magnetic element  10  (the resistance value of the magnetic element  10  in the z direction) changes. For example, when the first value (the first resistance value R 1 ) is defined as “0,” the second value (second resistance value R 2 ) is defined as “1,” the third value (third resistance value R 3 ) is defined as “2,” and the fourth value (fourth resistance value R 4 ) is defined as “3,” the photodetection element  100  can output information of four values. Although the case where four values are read is shown as an example here, the number of values to be read can be freely designed by setting the threshold value of the output voltage from the magnetic element  10  (the resistance value of the magnetic element  10 ). Also, the photodetection element  100  may output an analog value as it is. 
     Also, as in the case of  FIG. 5 , when the intensity of the light applied to the first ferromagnetic layer 1 changes, the magnitude of the magnetization M 1  of the first ferromagnetic layer 1 decreases from the initial state due to the external energy generated by the application of the light. When the magnetization M 1  of the first ferromagnetic layer 1 decreases from the initial state, the resistance value of the magnetoresistance effect element  10  in the z direction changes. The output voltage from the magnetic element  10  changes. For example, the resistance value of the magnetic element  10  in the z direction changes to the second resistance value R 2 , the third resistance value R 3 , and the fourth resistance value R 4  in accordance with the magnitude of the magnetization M 1  of the first ferromagnetic layer 1. The output voltage from the magnetic element  10  changes to the second value, the third value, and the fourth value. Therefore, as in the case of  FIG. 4 , the photodetection element  100  can output the difference in these output voltages (resistance values) as multi-valued or analog data. 
     Also, in the case of the second operation example, as in the case of the first operation example, when the intensity of the light applied to the first ferromagnetic layer 1 returns to the first intensity, the magnetization M 1  of the first ferromagnetic layer 1 returns to the original state and the magnetic element  10  returns to the initial state. 
     Although the case where the magnetization M 1  is parallel to the magnetization M 2  in the initial state has been described as an example here, the magnetization M 1  may also be antiparallel to the magnetization M 2  in the initial state in the second operation example. 
     As described above, the photodetection element  100  according to the first embodiment can replace the light with an electrical signal by replacing the light applied to the magnetic element  10  with the output voltage from the magnetic element  10 . Also, the presence of the first high thermal conductivity layer  20  having high thermal conductivity on the outside of the magnetic element  10  that generates heat with the application of light can promote heat dissipation from the magnetic element  10 . That is, when the application of light to the first ferromagnetic layer 1 is stopped, the magnetic element  10  is quickly cooled and the magnetization M 1  is quickly restored to the initial state. When the magnetization M 1  of the first ferromagnetic layer 1 returns to the initial state quickly, the response characteristics of the photodetection element  100  to light are improved. In other words, the speed of the response characteristic of the photodetection element  100  to light is increased. 
     Although the first embodiment has been described above in detail with reference to the drawings, the first embodiment is not limited to this example. 
     First Modified Example 
       FIG. 6  is a cross-sectional view of a photodetection element  101  according to a first modified example. The photodetection element  101  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  21 , insulating layers  30  and  31 , and a substrate  40 . In the first modified example, components similar to those in the first embodiment are denoted by similar reference signs and the description thereof will be omitted. 
     The first high thermal conductivity layer  21  is located outside of the first ferromagnetic layer 1 when viewed from the z direction. The first high thermal conductivity layer  21  is connected to the magnetic element  10  via, for example, the insulating layer  30 . The first high thermal conductivity layer  21  surrounds, for example, the circumference of at least a part of the magnetic element  10 . For example, the first high thermal conductivity layer  21  surrounds the circumference of the first ferromagnetic layer 1 of the magnetic element  10 . The first high thermal conductivity layer  21  is in contact with, for example, the first electrode  11 . The first high thermal conductivity layer  21  is sandwiched between the insulating layer  30  and the insulating layer  31 . 
     The first high thermal conductivity layer  21  has higher thermal conductivity than the first electrode  11 . The first high thermal conductivity layer  21  is made of a material similar to that of the first high thermal conductivity layer  20 . 
     The insulating layer  31  covers an upper surface of the first high thermal conductivity layer  21 . The insulating layer  31  sandwiches the first high thermal conductivity layer  21  with the insulating layer  30 . The insulating layer  31  is made of a material similar to that of the insulating layer  30 . 
     Because the photodetection element  101  according to the first modified example has the first high thermal conductivity layer  21 , the photodetection element  101  has effects similar to those of the photodetection element  100 . 
     Second Modified Example 
       FIG. 7  is a cross-sectional view of a photodetection element  102  according to a second modified example. The photodetection element  102  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  22 , insulating layers  30  and  31 , and a substrate  40 . In the second modified example, components similar to those in the first modified example are denoted by similar reference signs and the description thereof will be omitted. 
     The first high thermal conductivity layer  22  is located outside of the first ferromagnetic layer 1 when viewed from the z direction. The first high thermal conductivity layer  22  is different from the first high thermal conductivity layer  21  according to the first modified example in that the first high thermal conductivity layer  22  is not in contact with the first electrode  11 . 
     Because the photodetection element  102  according to the second modified example has the first high thermal conductivity layer  22 , the photodetection element  102  has effects similar to those of the photodetection element  100 . 
     Third Modified Example 
       FIG. 8  is a cross-sectional view of a photodetection element  103  according to a third modified example. The photodetection element  103  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  20 , an insulating layer  30 , a substrate  40 , and a second high thermal conductivity layer  50 . In the third modified example, components similar to those in the first embodiment are denoted by similar reference signs and the description thereof will be omitted. 
     The second high thermal conductivity layer  50  is in contact with a sidewall of the first electrode  11 . The second high thermal conductivity layer  50  surrounds, for example, the circumference of the first electrode  11 . The second high thermal conductivity layer  50  has higher thermal conductivity than the first electrode  11 . The second high thermal conductivity layer  50  is in contact with, for example, the first high thermal conductivity layer  20 . When the second high thermal conductivity layer  50  and the first high thermal conductivity layer  20  come into contact with each other, heat can be expelled from the first high thermal conductivity layer  20  toward the second high thermal conductivity layer  50  and heat is efficiently dissipated from the magnetic element  10 . A material similar to that of the first high thermal conductivity layer  20  can be applied to the second high thermal conductivity layer  50 . The first high thermal conductivity layer  20  and the second high thermal conductivity layer  50  may be made of the same material or different materials. 
     Because the photodetection element  103  according to the third modified example has the first high thermal conductivity layer  20 , the photodetection element  103  has effects similar to those of the photodetection element  100 . Also, the photodetection element  103  has the second high thermal conductivity layer  50 , so that the photodetection element  103  is more excellent in heat dissipation. 
     Fourth Modified Example 
       FIG. 9  is a cross-sectional view of a photodetection element  104  according to a fourth modified example. The photodetection element  104  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  23 , an insulating layer  32 , and a substrate  40 . In the fourth modified example, components similar to those in the first embodiment are denoted by similar reference signs and the description thereof will be omitted. 
     The first high thermal conductivity layer  23  is located outside of the first ferromagnetic layer 1 when viewed from the z direction. The first high thermal conductivity layer  23  is in direct contact with the magnetic element  10 . The first high thermal conductivity layer  23  is in direct contact with, for example, at least a part of the side surface of the first ferromagnetic layer 1. The first high thermal conductivity layer  23  surrounds the circumference of at least a part of the magnetic element  10 . For example, the first high thermal conductivity layer  23  surrounds the circumference of the first ferromagnetic layer 1 of the magnetic element  10 . 
     The first high thermal conductivity layer  23  has higher thermal conductivity than the first electrode  11 . The first high thermal conductivity layer  23  is made of a material similar to that of the first high thermal conductivity layer  20 . 
     A part of the insulating layer  32  is located between the magnetic element  10  and the first high thermal conductivity layer  23 . The insulating layer  32  is made of a material similar to that of the insulating layer  30 . The insulating layer  32  covers at least a portion below a lower end  3 U of the spacer layer 3 within a sidewall of the magnetic element  10 . By covering the portion below the lower end  3 U of the spacer layer 3, the insulating layer  32  can prevent the first high thermal conductivity layer  23  and the second ferromagnetic layer 2 from being short-circuited even if the first high thermal conductivity layer  23  is a conductor. 
     Because the photodetection element  104  according to the fourth modified example has the first high thermal conductivity layer  23 , the photodetection element  104  has effects similar to those of the photodetection element  100 . Also, when the first high thermal conductivity layer  23  is in direct contact with the first ferromagnetic layer 1, the heat generated in the first ferromagnetic layer 1 can be dissipated more efficiently. Also, when the first high thermal conductivity layer  23  is a conductor, the insulating layer  32  prevents the first high thermal conductivity layer  23  and the second ferromagnetic layer 2 from being short-circuited, so that the deterioration of the magnetic characteristics of the magnetic element  10  can be limited. 
     Fifth Modified Example 
       FIG. 10  is a cross-sectional view of a photodetection element  105  according to a fifth modified example. The photodetection element  105  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  25 , and a substrate  40 . In the fifth modified example, components similar to those in the first embodiment are denoted by similar reference signs and the description thereof will be omitted. 
     The first high thermal conductivity layer  25  is located outside of the first ferromagnetic layer 1 when viewed from the z direction. The first high thermal conductivity layer  25  is in direct contact with the magnetic element  10 . The first high thermal conductivity layer  25  surrounds the circumference of the magnetic element  10 . 
     The first high thermal conductivity layer  25  has higher thermal conductivity than the first electrode  11 . The first high thermal conductivity layer  25  is an insulator. The thermal conductivity of the first high thermal conductivity layer  25  is, for example, greater than 40 W/m·K. The first high thermal conductivity layer  25  includes, for example, silicon carbide, aluminum nitride, or boron nitride. 
     Because the photodetection element  105  according to the fifth modified example has the first high thermal conductivity layer  25 , the photodetection element  105  has effects similar to those of the photodetection element  100 . Also, because the first high thermal conductivity layer  25  has an insulating property, it can be in direct contact with the entire side surface of the magnetic element  10 . As a result, the photodetection element  105  can efficiently dissipate heat from the magnetic element  10 . 
     Sixth Modified Example 
       FIG. 11  is a cross-sectional view of a photodetection element  106  according to a sixth modified example. The photodetection element  106  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  26 , a substrate  40 , and a high resistivity layer  60 . In the sixth modified example, components similar to those in the first embodiment are denoted by similar reference signs and the description thereof will be omitted. 
     The first high thermal conductivity layer  26  is located outside of the first ferromagnetic layer 1 when viewed from the z direction. The first high thermal conductivity layer  26  is in direct contact with, for example, the first ferromagnetic layer 1. The high resistivity layer  60  may be provided between the first high thermal conductivity layer  26  and the first ferromagnetic layer 1. The first high thermal conductivity layer  26  surrounds, for example, the circumference of the first ferromagnetic layer 1. 
     The first high thermal conductivity layer  26  has higher thermal conductivity than the first electrode  11 . The first high thermal conductivity layer  26  is an insulator. The thermal conductivity of the first high thermal conductivity layer  26  is, for example, greater than 40 W/m·K. The first high thermal conductivity layer  26  includes, for example, silicon carbide, aluminum nitride, or boron nitride. 
     The high resistivity layer  60  is located between the first high thermal conductivity layer  26  and the second electrode  12 . A part of the high resistivity layer  60  may be located between the magnetic element  10  and the first high thermal conductivity layer  26 . The high resistivity layer  60  has higher resistivity than the first high thermal conductivity layer  26 . 
     The high resistivity layer  60  is, for example, an insulator. The high resistivity layer  60  depends on a material constituting the first high thermal conductivity layer  26 , but is, for example, aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), forsterite (2MgO.SiO 2 ), yttrium oxide (Y 2 O 3 ), aluminum nitride (AlN), or boron nitride (BN). 
     For example, when the first high thermal conductivity layer  26  is silicon carbide (SiC), the high resistivity layer  60  may be aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), forsterite (2MgO.SiO 2 ), yttrium oxide (Y 2 O 3 ), aluminum nitride (AlN), or boron nitride (BN). For example, when the first high thermal conductivity layer  26  is aluminum nitride (AlN) or boron nitride (BN), the high resistivity layer  60  may be silicon oxide (SiO 2 ). 
     Because the photodetection element  106  according to the sixth modified example has the first high thermal conductivity layer  26 , the photodetection element  106  has effects similar to those of the photodetection element  100 . Also, the high resistivity layer  60  is provided between the first electrode  11  and the second electrode  12 , so that the insulating property between the first electrode  11  and the second electrode  12  can be enhanced. 
     Seventh Modified Example 
       FIG. 12  is a cross-sectional view of a photodetection element  107  according to a seventh modified example. The photodetection element  107  includes, for example, a magnetic element  10 , a first electrode  11 , a second electrode  12 , a first high thermal conductivity layer  26 , a substrate  40 , and a low dielectric constant layer  70 . In the seventh modified example, components similar to those in the sixth modified example are denoted by similar reference signs and the description thereof will be omitted. 
     The low dielectric constant layer  70  is located between the first high thermal conductivity layer  26  and the second electrode  12 . A part of the low dielectric constant layer  70  may be located between the magnetic element  10  and the first high thermal conductivity layer  26 . The low dielectric constant layer  70  has a lower dielectric constant than the first high thermal conductivity layer  26 . 
     The low dielectric constant layer  70  is, for example, an insulator. The low dielectric constant layer  70  depends on the material constituting the first high thermal conductivity layer  26 , but, is for example, silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), forsterite (2MgO.SiO 2 ), aluminum nitride (AlN), or boron nitride (BN). 
     For example, when the first high thermal conductivity layer  26  is silicon carbide (SiC), the low dielectric constant layer  70  may be silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), forsterite (2MgO.SiO 2 ), aluminum nitride (AlN), or boron nitride (BN). For example, when the first high thermal conductivity layer  26  is aluminum nitride (AlN), the low dielectric constant layer  70  may be silicon oxide (SiO 2 ), forsterite (2MgO.SiO 2 ), or boron nitride (BN). For example, when the first high thermal conductivity layer  26  is boron nitride (BN), the low dielectric constant layer  70  may be silicon oxide (SiO 2 ). 
     Because the photodetection element  107  according to the seventh modified example has the first high thermal conductivity layer  26 , the photodetection element  107  has effects similar to those of the photodetection element  100 . Also, the low dielectric constant layer  70  is provided between the first electrode  11  and the second electrode  12 , so that the capacitance between the first electrode  11  and the second electrode  12  can be reduced. 
     The present disclosure is not limited to the above-described embodiments and modified examples and various modifications and changes can be made within the scope of the subject matter of the present disclosure described within the scope of the claims. For example, the feature configurations of the above-described embodiment and modified examples may be combined. 
     The photodetection element according to the above-described embodiment and modified example can be applied to an optical sensor device such as an image sensor, a transceiver device of a communication system, or the like. 
       FIG. 13  is a block diagram of the transceiver device  1000  according to the first application example. The transceiver device  1000  includes a receiving device  300  and a transmission device  400 . The receiving device  300  receives an optical signal L 1  and the transmission device  400  transmits an optical signal L 2 . 
     The receiving device  300  includes, for example, a photodetection element  301  and a signal processing unit  302 . The photodetection element  301  is any one of the photodetection elements  100  to  107  according to any one of the above-described embodiments and modified examples. The photodetection element  301  converts the optical signal L 1  into an electrical signal. The operation of the photodetection element  301  may be either the first operation example or the second operation example. Light including the optical signal L 1  having a change in an intensity of light is applied to the first ferromagnetic layer 1 of the photodetection element  301 . A lens may be disposed on the side of the first ferromagnetic layer 1 in the lamination direction of the photodetection element  301 , so that light condensed through the lens may be applied to the first ferromagnetic layer 1. The lens may be formed in the wafer process of forming the photodetection element  301 . Also, the light passing through the waveguide may be applied to the first ferromagnetic layer 1 of the photodetection element  301 . The light applied to the first ferromagnetic layer 1 of the photodetection element  301  is, for example, laser light. The signal processing unit  302  processes the electrical signal obtained in the conversion process of the photodetection element  301 . The signal processing unit  302  receives a signal included in the optical signal L 1  by processing the electrical signal generated from the photodetection element  301 . 
     The transmission device  400  includes, for example, a light source  401 , an electrical signal generation element  402 , and a light modulation element  403 . The light source  401  is, for example, a laser element. The light source  401  may be located outside of the transmission device  400 . The electrical signal generation element  402  generates an electrical signal on the basis of the transmission information. The electrical signal generation element  402  may be integrated with the signal conversion element of the signal processing unit  302 . The light modulation element  403  modulates light output from the light source  401  on the basis of the electrical signal generated by the electrical signal generation element  402  and outputs the optical signal L 2 . 
       FIG. 14  is a conceptual diagram of an example of a communication system. The communication system shown in  FIG. 14  has two terminal devices  500 . The terminal device  500  is, for example, a smartphone, a tablet, a personal computer, or the like. 
     Each of the terminal devices  500  includes a receiving device  300  and a transmission device  400 . An optical signal transmitted from the transmission device  400  of one terminal device  500  is received by the receiving device  300  of the other terminal device  500 . The light used for transmission/receiver between the terminal devices  500  is, for example, visible light. The receiving device  300  has one of the above-described photodetection elements  100  to  107  as the photodetection element  301 . Because the above-described photodetection elements  100  to  107  are excellent in heat dissipation, the communication system shown in  FIG. 14  can implement high-speed communication. 
       FIG. 15  is a conceptual diagram of a cross-section of an optical sensor device  2000  according to the second application example. The optical sensor device  2000  includes, for example, a circuit board  110 , a wiring layer  120 , and a plurality of optical sensors S. Each of the wiring layer  120  and the plurality of optical sensors S is formed on the circuit board  110 . 
     Each of the plurality of optical sensors S includes, for example, a photodetection element  100 , a wavelength filter F, and a lens R. Although an example in which the photodetection element  100  is used is shown in  FIG. 15 , the photodetection elements  101  to  106  may be used instead of the photodetection element  100 . Light passing through the wavelength filter F is applied to the photodetection element  100 . As described above, the photodetection element  100  replaces the light applied to the magnetic element  10  with an electrical signal. The photodetection element  100  may operate in the second operation example. 
     The wavelength filter F selects light of a specific wavelength and transmits light of a specific wavelength range. The wavelength range of light transmitted by each wavelength filter F may be the same or different. For example, the optical sensor device  2000  may include an optical sensor S (hereinafter referred to as a blue sensor) having a wavelength filter F that transmits light in blue (a wavelength range of 380 nm or more and less than 490 nm), an optical sensor S (hereinafter referred to as a green sensor) having a wavelength filter F that transmits light in green (a wavelength range of 490 nm or more and less than 590 nm), and an optical sensor S (hereinafter referred to as a red sensor) having a wavelength filter F that transmits light in red (a wavelength range of 590 nm or more and less than 800 nm). The blue sensor, the green sensor, and the red sensor are set as one pixel, and the optical sensor device  2000  can be used as an image sensor by arraying these pixels. 
     The lens R condenses light toward the magnetic element  10 . Although one photodetection element  100  is disposed below one wavelength filter F in the optical sensor S shown in  FIG. 15 , a plurality of photodetection elements  100  may be disposed below one wavelength filter F. 
     The circuit board  110  has, for example, an analog-to-digital converter  111  and an output terminal  112 . An electrical signal sent from the optical sensor S is replaced with digital data by the analog-to-digital converter  111  and is output from the output terminal  112 . 
     The wiring layer  120  has two or more wirings  121 . There is an interlayer insulating film  122  between the two or more wirings  121 . The wiring  121  is electrically connected between each of the optical sensors S and the circuit board  110  and is electrically connected to each calculation circuit formed on the circuit board  110 . Each of the optical sensors S and the circuit board  110  are connected, for example, via through-wiring passing through the interlayer insulating film  122  in the z direction. Noise can be reduced by shortening an inter-wiring distance between each of the optical sensors S and the circuit board  110 . 
     The wiring  121  has conductivity. The wiring  121  is, for example, Al, Cu, or the like. The interlayer insulating film  122  is an insulator that provides insulation between the wirings of the multilayer wiring and between the elements. The interlayer insulating film  122  is, for example, an oxide, a nitride, or an oxynitride of Si, Al, or Mg. The interlayer insulating film  122  is, for example, silicon oxide (SiO x ), silicon nitride (SiN x ), silicon carbide (SiC), chromium nitride, silicon nitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO x ), or the like. 
     The above-described optical sensor device  2000  can be used, for example, in a terminal device.  FIG. 16  is a schematic view of an example of a terminal device  600 . The left side of  FIG. 16  is a front surface of the terminal device  600  and the right side of  FIG. 16  is a back surface of the terminal device  600 . The terminal device  600  has a camera CA. The above-described optical sensor device  2000  can be used as an image sensor of this camera CA. Although a smartphone is shown as an example of the terminal device  600  in  FIG. 16 , the present disclosure is not limited to this case. The terminal device  600  is, for example, a tablet, a personal computer, a digital camera, or the like other than the smartphone.