Light detection device

Abstract

To provide a light detection device hardly affected by disturbance.SOLUTION: A light detection device includes a first terminal, a second terminal, a third terminal, a fourth terminal, a first element, a second element, a third element, and a fourth element. The first terminal, the first element, the second element, and the second terminal form a first path. The first terminal, the third element, the fourth element, and the second terminal form a second path. The third terminal is connected between the first element and the second element. The fourth terminal is connected between the third element and the fourth element. Each of the first element, the second element, the third element, and the fourth element includes a photosensitive layer that generates a voltage when irradiated with light. The photosensitive layer of the first element is irradiated with light to be measured. The photosensitive layers of the second element and the third element are not irradiated with light to be measured.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light sensing device. [Background technology]

[0002] Photoelectric conversion elements are used for a variety of purposes.

[0003] 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 that uses a semiconductor pn junction, and converts light into an electrical signal.

[0004] Furthermore, for example, a novel optical device using a magnetic element is disclosed in Patent Document 2. When the magnetic element is irradiated with light, the magnetic state changes, and the resistance value also changes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-292107 [Patent Document 2] Japanese Patent Application Publication No. 2023-90284 Summary of the Invention [Problem to be solved by the invention]

[0006] Photodetectors convert light into electrical signals. For example, photodetectors using magnetic elements may experience changes in output due to disturbances such as temperature and magnetic fields. Therefore, the effects of disturbances cannot be ignored when measuring light intensity using a photodetector, and there is a demand for photodetectors that are less susceptible to disturbances.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a light detection device that is less susceptible to the influence of external disturbances. [Means for solving the problem]

[0008] In order to solve the above problems, the following means are provided.

[0009] The photodetector according to this embodiment includes a first terminal, a second terminal, a third terminal, a fourth terminal, a first element, a second element, a third element, and a fourth element. The first terminal, the first element, the second element, and the second terminal form a first path. The first terminal, the third element, the fourth element, and the second terminal form a second path. The third terminal is connected between the first element and the second element. The fourth terminal is connected between the third element and the fourth element. Each of the first element, the second element, the third element, and the fourth element includes a first electrode, a second electrode, and a photosensitive layer located between the first electrode and the second electrode and generating a voltage when irradiated with light. The photosensitive layer of the first element is irradiated with light to be measured. The photosensitive layer of the second element and the third element is not irradiated with light to be measured. [Effects of the Invention]

[0010] The light detection device according to the above aspect is less susceptible to disturbances. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a plan view of a light detection device according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the vicinity of a first element of the photodetector according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the vicinity of a second element of the photodetector according to the first embodiment. [Figure 4] 4A to 4C are diagrams illustrating an example of the operation of the first element according to the first embodiment. [Figure 5] 4A to 4C are diagrams illustrating an example of the operation of the first element according to the first embodiment. [Figure 6] FIG. 10 is a cross-sectional view of the vicinity of a second element of a photodetector according to a first modified example of the first embodiment. [Figure 7]FIG. 10 is a cross-sectional view of the vicinity of a second element of a photodetector according to a second modified example of the first embodiment. [Figure 8] FIG. 10 is a plan view of a light detection device according to a second embodiment. [Figure 9] FIG. 10 is a plan view of a light detection device according to a third embodiment. [Figure 10] FIG. 10 is a plan view of a light detection device according to a fourth embodiment. [Figure 11] FIG. 10 is a cross-sectional view of the vicinity of a first element of a photodetector according to a fourth embodiment. [Figure 12] FIG. 10 is a cross-sectional view of the vicinity of a second element of a photodetector according to a fourth embodiment. [Figure 13] FIG. 10 is a plan view of a light detection device according to a fifth embodiment. [Figure 14] FIG. 10 is a plan view of a light detection device according to a sixth embodiment. [Figure 15] FIG. 1 is a schematic diagram of an optical element according to a first application example. [Figure 16] FIG. 1 is a conceptual diagram of an optical system using an optical element according to a first application example. [Figure 17] FIG. 10 is a schematic diagram of a transmitting / receiving device according to a second application example. [Figure 18] FIG. 1 is a conceptual diagram of an example of a communication system. [Figure 19] FIG. 1 is a conceptual diagram of another example of a communication system. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate changes can be made within the scope of the effects of the present invention.

[0013] The directions are defined as follows. The direction within the plane of the surface on which each layer extends is the X direction, and the direction within the plane perpendicular to the X direction is the Y direction. The stacking direction perpendicular to each layer is the Z direction. Hereinafter, the +Z direction may be expressed as "up" and the -Z direction as "down". The +Z direction is the direction from the second electrode 22 to the first electrode 21. Up and down do not necessarily coincide with the direction in which gravity is applied.

[0014] "First embodiment" 1 is a plan view of a photodetector 100 according to a first embodiment. The photodetector 100 includes a first terminal t1, a second terminal t2, a third terminal t3, a fourth terminal t4, a first element 1, a second element 2, a third element 3, and a fourth element 4.

[0015] The first terminal t1 is connected to, for example, a power supply. The first terminal t1 is connected to each of the first element 1 and the third element 3. The second terminal t2 is connected to, for example, a reference potential. The reference potential is, for example, ground. The second terminal t2 is connected to each of the second terminal t2 and the fourth terminal t4.

[0016] Two current paths are formed between the first terminal t1 and the second terminal t2. The first path connects the first terminal t1, the first element 1, the second element 2, and the second terminal t2. The second path connects the first terminal t1, the third element 3, the fourth element 4, and the second terminal t2. The first path and the second path are electrically in parallel.

[0017] The third terminal t3 is connected to each of the first element 1 and the second element 2. The third terminal t3 is connected, for example, to the upper electrode 23 that electrically connects the first element 1 and the second element 2. The fourth terminal t4 is connected to each of the third element 3 and the fourth element 4. The fourth terminal t4 is connected, for example, to the upper electrode 23 that electrically connects the third element 3 and the fourth element 4. The photodetector 100 measures the potential difference between the third terminal t3 and the fourth terminal t4.

[0018] The first element 1, the second element 2, the third element 3, and the fourth element 4 are each a photodetector element. Hereinafter, when the first element 1, the second element 2, the third element 3, and the fourth element 4 are described without distinction, they may be collectively referred to as photodetectors. The first element 1 is electrically located between the first terminal t1 and the third terminal t3. The second element 2 is electrically located between the third terminal t3 and the second terminal t2. The third element 3 is electrically located between the first terminal t1 and the fourth terminal t4. The fourth element 4 is electrically located between the fourth terminal t4 and the second terminal t2.

[0019] The first element 1, the second element 2, the third element 3, and the fourth element 4 are arranged so as to fall within the spot of light irradiated onto the photodetector 100. The spot is the range where light is irradiated onto the irradiated object. The spot is a continuous area including the center, and is the range where light with an intensity of 13.5% or more of the light intensity at the center is irradiated. The range of the light spot is determined by an optical element. The optical element is, for example, a waveguide, a lens, a light source, etc.

[0020] Light L is not limited to visible light, but also includes infrared light, which has a longer wavelength than visible light, and ultraviolet light, which has 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 light is, for example, 800 nm or more and 1 mm or less. The wavelength of ultraviolet light is, for example, 200 nm or more and less than 380 nm. The light may be, for example, light that includes a high-frequency optical signal and whose intensity varies, or light whose wavelength range is controlled (for example, light that has passed through a wavelength filter). The high-frequency optical signal is, for example, a signal having a frequency of 100 MHz or more.

[0021] Fig. 2 is a cross-sectional view of the vicinity of the first element 1 of the photodetector 100 according to the first embodiment. Fig. 3 is a cross-sectional view of the vicinity of the second element 2 of the photodetector 100 according to the first embodiment. The third element 3 and the fourth element 4 have the same configuration as the second element 2, and are therefore not shown.

[0022] Each of the first element 1, the second element 2, the third element 3, and the fourth element 4 includes a first electrode 21, a second electrode 22, and a photosensitive layer 10. The photosensitive layer 10 is located between the first electrode 21 and the second electrode 22.

[0023] Each of the first element 1, the second element 2, the third element 3, and the fourth element 4 may further include a buffer layer 14, a seed layer 15, a third ferromagnetic layer 16, a magnetic coupling layer 17, a perpendicular magnetization induction layer 18, a cap layer 19, an insulating layer 30, and an insulating layer 31. The buffer layer 14, the seed layer 15, the third ferromagnetic layer 16, and the magnetic coupling layer 17 are located between the photosensitive layer 10 and the second electrode 22, and the perpendicular magnetization induction layer 18 and the cap layer 19 are located between the photosensitive layer 10 and the first electrode 21. The insulating layer 30 is located between the first electrode 21 and the second electrode 22 and covers the periphery of the stack including the photosensitive layer 10. The insulating layer 31 covers the top of the first electrode 21. The insulating layer 31 is optional.

[0024] The photosensitive layer 10 generates a voltage when irradiated with light. When the state of the irradiated light changes, the resistance value of the photosensitive layer 10 in the Z direction changes in response to the change in the state of the light. When the state of the light irradiated to the photosensitive layer 10 changes, the output voltage from the photodetector changes in response to the change in the state of the light. The photosensitive layer 10 includes, for example, a first ferromagnetic layer 11, a second ferromagnetic layer 12, and a spacer layer 13. The spacer layer 13 is located between the first ferromagnetic layer 11 and the second ferromagnetic layer 12. The photosensitive layer 10 may include other layers in addition to these.

[0025] The photosensitive layer 10 is a magnetic element containing a ferromagnetic material. For example, when the spacer layer 13 is made of an insulator, the photosensitive layer 10 has a magnetic tunnel junction (MTJ) consisting of the first ferromagnetic layer 11, the spacer layer 13, and the second ferromagnetic layer 12. Such an element is called an MTJ element. In this case, the photosensitive layer 10 can exhibit a tunnel magnetoresistance (TMR) effect. When the spacer layer 13 is made of a metal, the photosensitive layer 10 can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element. The photosensitive layer 10 may be called an MTJ element, a GMR element, or other names depending on the material of the spacer layer 13, but is also collectively called a magnetoresistance effect element. The photosensitive layer 10 has a magnetoresistive effect element (MTJ) consisting of the magnetization M of the first ferromagnetic layer 11. 11 and the magnetization M of the second ferromagnetic layer 12 12 The resistance value in the Z direction (resistance value when current flows in the Z direction) changes depending on the relative change with respect to the state of

[0026] The first ferromagnetic layer 11 is a photodetector layer whose magnetization state changes when irradiated with light from the outside. The first ferromagnetic layer 11 is also called a 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 direction of the photosensitive layer 10, or an external magnetic field. The magnetization M of the first ferromagnetic layer 11 11 The state changes depending on the intensity of the light irradiated to the first ferromagnetic layer 11 (light irradiated to the photosensitive layer 10).

[0027] The first ferromagnetic layer 11 includes a ferromagnetic material. The first ferromagnetic layer 11 includes at least one of magnetic elements such as Co, Fe, or Ni. The first ferromagnetic layer 11 may include elements such as B, Mg, Hf, or Gd in addition to the magnetic elements described above. The first ferromagnetic layer 11 may be, for example, an alloy including a magnetic element and a non-magnetic element. The first ferromagnetic layer 11 may be composed of multiple layers. The first ferromagnetic layer 11 may be, for example, a CoFeB alloy, a stacked body in which a CoFeB alloy layer is sandwiched between Fe layers, or a stacked body in which a CoFeB alloy layer is sandwiched between CoFe layers. Generally, "ferromagnetic" includes "ferrimagnetic." The first ferromagnetic layer 11 may exhibit ferrimagnetic properties. On the other hand, the first ferromagnetic layer 11 may exhibit ferromagnetic properties that are not ferrimagnetic. For example, a CoFeB alloy exhibits ferromagnetic properties that are not ferrimagnetic.

[0028] The first ferromagnetic layer 11 may be an in-plane magnetization film having an axis of easy magnetization in the in-plane direction (any direction in the XY plane) or a perpendicular magnetization film having an axis of easy magnetization in the direction perpendicular to the film plane (Z direction).

[0029] The thickness of the first ferromagnetic layer 11 is, for example, 1 nm or more and 5 nm or less. The thickness of the first ferromagnetic layer 11 is preferably, for example, 1 nm or more and 2 nm or less. When the first ferromagnetic layer 11 is a perpendicular magnetization film, if the thickness of the first ferromagnetic layer 11 is thin, the perpendicular magnetic anisotropy application effect from the layers above and below the first ferromagnetic layer 11 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 11 is enhanced. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 11 is high, the magnetization M 11 On the other hand, if the first ferromagnetic layer 11 is thick, the effect of applying perpendicular magnetic anisotropy from the layers above and below the first ferromagnetic layer 11 becomes relatively weaker, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 11 weakens.

[0030] When the thickness of the first ferromagnetic layer 11 is reduced, the volume of the ferromagnetic material is reduced, and when the thickness is increased, the volume of the ferromagnetic material is increased. The magnetization M of the first ferromagnetic layer 11 when external energy is applied is 11The reactivity of the first ferromagnetic layer 11 is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and the volume (V) of the first ferromagnetic layer 11. In other words, the reactivity to light increases as the product of the magnetic anisotropy and the volume of the first ferromagnetic layer 11 decreases. From this perspective, in order to increase the reactivity to light, it is preferable to reduce the volume of the first ferromagnetic layer 11 after appropriately designing the magnetic anisotropy of the first ferromagnetic layer 11.

[0031] If the thickness of the first ferromagnetic layer 11 is greater than 2 nm, an insertion layer made of, for example, Mo or W may be provided within the first ferromagnetic layer 11. That is, the first ferromagnetic layer 11 may be a stack in which a ferromagnetic layer, an insertion layer, and a ferromagnetic layer are stacked in this order in the Z direction. The interfacial magnetic anisotropy at the interface between the insertion layer and the ferromagnetic layer enhances the perpendicular magnetic anisotropy of the entire first ferromagnetic layer 11. The thickness of the insertion layer is, for example, 0.1 nm to 1.0 nm.

[0032] The second ferromagnetic layer 12 is a magnetization fixed layer. The magnetization fixed layer has a magnetization M 12 The second ferromagnetic layer 12 is a layer made of a magnetic material whose state is less likely to change than the magnetization free layer. For example, the magnetization direction of the magnetization fixed layer is less likely to change than the magnetization free layer when a predetermined external energy is applied. Also, for example, the magnitude of the magnetization of the magnetization fixed layer is less likely to change than the magnetization free layer when a predetermined external energy is applied. The coercive force of the second ferromagnetic layer 12 is greater than the coercive force of the first ferromagnetic layer 11. The second ferromagnetic layer 12 has an easy axis of magnetization in the same direction as the first ferromagnetic layer 11, for example. The second ferromagnetic layer 12 may be an in-plane magnetization film or a perpendicular magnetization film.

[0033] The material constituting the second ferromagnetic layer 12 is, for example, the same as that of the first ferromagnetic layer 11. The second ferromagnetic layer 12 may be, for example, a multilayer film in which Co layers having a thickness of 0.4 nm to 1.0 nm and Pt layers having a thickness of 0.4 nm to 1.0 nm are alternately stacked several times. The second ferromagnetic layer 12 may be, for example, a laminate in which Co layers having a thickness of 0.4 nm to 1.0 nm, Mo layers having a thickness of 0.1 nm to 0.5 nm, a CoFeB alloy layers having a thickness of 0.3 nm to 1.0 nm, and Fe layers having a thickness of 0.3 nm to 1.0 nm are stacked in this order.

[0034] The magnetization M of the second ferromagnetic layer 12 12 is, for example, the magnetization M of the third ferromagnetic layer 16 16 The magnetization may be fixed by magnetic coupling with the second ferromagnetic layer 12. In this case, the combination of the second ferromagnetic layer 12, the magnetic coupling layer 17, and the third ferromagnetic layer 16 may be referred to as a magnetization fixed layer. The magnetic coupling layer 17 and the third ferromagnetic layer 16 will be described in detail later.

[0035] The spacer layer 13 is a layer disposed between the first ferromagnetic layer 11 and the second ferromagnetic layer 12. The spacer layer 13 is a layer made of a conductor, an insulator, or a semiconductor, or a layer containing current-carrying points made of a conductor in an insulator. The spacer layer 13 is, for example, a non-magnetic layer. The thickness of the spacer layer 13 is determined based on the magnetization M of the first ferromagnetic layer 11 in the initial state, which will be described later. 11 and the magnetization M of the second ferromagnetic layer 12 12 The orientation direction of the film can be adjusted.

[0036] When the spacer layer 13 is made of an insulating material, a material containing aluminum oxide, magnesium oxide, titanium oxide, silicon oxide, or the like can be used as the material for the spacer layer 13. 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 magnetoresistance ratio can be obtained by adjusting the thickness of the spacer layer 13 so that a high TMR effect is exhibited between the first ferromagnetic layer 11 and the second ferromagnetic layer 12. To efficiently utilize the TMR effect, the thickness of the spacer layer 13 may be approximately 0.5 to 5.0 nm, or approximately 1.0 to 2.5 nm.

[0037] When the spacer layer 13 is made of a nonmagnetic conductive material, conductive materials such as Cu, Ag, Au, or Ru can be used. To efficiently utilize the GMR effect, the thickness of the spacer layer 13 may be about 0.5 to 5.0 nm, or about 2.0 to 3.0 nm.

[0038] When the spacer layer 13 is made of a non-magnetic semiconductor material, it can be made of zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, ITO, etc. In this case, the thickness of the spacer layer 13 may be about 1.0 to 4.0 nm.

[0039] When a layer including current-carrying points formed by a conductor in a nonmagnetic insulator is used as the spacer layer 13, the current-carrying points may be formed by a nonmagnetic conductor such as Cu, Au, or Al in a nonmagnetic insulator made of aluminum oxide or magnesium oxide. The conductor may also be formed of a magnetic element such as Co, Fe, or Ni. In this case, the thickness of the spacer layer 13 may be approximately 1.0 to 2.5 nm. The current-carrying points are, for example, columnar bodies with a diameter of 1 nm to 5 nm when viewed perpendicular to the film surface.

[0040] The third ferromagnetic layer 16 is magnetically coupled to, for example, the second ferromagnetic layer 12. The magnetic coupling is, for example, antiferromagnetic coupling, which occurs due to RKKY interaction. The material constituting the third ferromagnetic layer 16 is, for example, the same as that of the first ferromagnetic layer 11.

[0041] The magnetic coupling layer 17 is located between the second ferromagnetic layer 12 and the third ferromagnetic layer 16. The magnetic coupling layer 17 is made of, for example, Ru, Ir, or the like.

[0042] The buffer layer 14 is a layer that reduces lattice mismatch between different crystals. The buffer layer 14 is, for example, a metal containing at least one element selected from the group consisting of Ta, Ti, Zr, and Cr, or a nitride containing at least one element selected from the group consisting of Ta, Ti, Zr, and Cu. More specifically, the buffer layer 14 is, for example, Ta (element), a NiCr alloy, TaN (tantalum nitride), or CuN (copper nitride). The buffer layer 14 has a thickness of, for example, 1 nm or more and 5 nm or less. The buffer layer 14 is, for example, amorphous. The buffer layer 14 is, for example, located between the seed layer 15 and the second electrode 22 and in contact with the second electrode 22. The buffer layer 14 prevents the crystal structure of the second electrode 22 from affecting the crystal structure of the photosensitive layer 10.

[0043] The seed layer 15 improves the crystallinity of the layers stacked on the seed layer 15. The seed layer 15 is located, for example, between the buffer layer 14 and the third ferromagnetic layer 16 and on the buffer layer 14. The seed layer 15 is made of, for example, Pt, Ru, Zr, or NiFeCr. The thickness of the seed layer 15 is, for example, 1 nm or more and 5 nm or less.

[0044] The cap layer 19 is located between the first ferromagnetic layer 11 and the first electrode 21. The cap layer 19 may include a perpendicular magnetization induction layer 18 stacked on the first ferromagnetic layer 11 and in contact with the first ferromagnetic layer 11. The cap layer 19 prevents damage to the lower layers during the process and improves the crystallinity of the lower layers during annealing. The thickness of the cap layer 19 is, for example, 10 nm or less so that the first ferromagnetic layer 11 is irradiated with sufficient light.

[0045] The perpendicular magnetization induction layer 18 induces perpendicular magnetic anisotropy in the first ferromagnetic layer 11. The perpendicular magnetization induction layer 18 is made of, for example, magnesium oxide, W, Ta, or Mo. When the perpendicular magnetization induction layer 18 is made of magnesium oxide, it is preferable that the magnesium oxide has oxygen deficiency to increase conductivity. The film thickness of the perpendicular magnetization induction layer 18 is, for example, 0.5 nm or more and 5.0 nm or less.

[0046] The insulating layers 30 and 31 are made of, for example, an oxide, nitride, or oxynitride of Si, Al, or Mg. The insulating layers 30 and 31 are made of, for example, silicon oxide (SiO x ), silicon nitride (SiN x ), silicon carbide (SiC), chromium nitride, silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al2O3), zirconium oxide (ZrO x ) etc.

[0047] The first electrode 21 is disposed on the side of the photodetector element where incident light is incident. The incident light is irradiated onto the photosensitive layer 10 from the first electrode 21 side. The first electrode 21 is made of a conductive material. The first electrode 21 is, for example, a transparent electrode that is transparent to light in the wavelength range used. The first electrode 21 preferably transmits, for example, 80% or more of light in the wavelength range used. The wavelength range used for light is, for example, 300 nm to 2 μm, preferably 400 nm to 1500 nm, or may be 400 nm to 800 nm. The first electrode 21 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 21 may be configured to include multiple metal pillars in a transparent electrode material made of these oxides. The first electrode 21 may also have an anti-reflection coating on the surface irradiated with light.

[0048] The second electrode 22 is made of a conductive material. The second electrode 22 is made of a metal such as Cu, Al, or Au. Ta or Ti may be laminated above and below these metals. The second electrode 22 may be a laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN. The second electrode 22 may also be TiN or TaN.

[0049] The second electrode 22 may be, for example, a metal containing at least one element selected from the group consisting of ruthenium, molybdenum, and tungsten. The second electrode 22 may be a single layer film of ruthenium, molybdenum, or tungsten, or a laminate film having at least one layer of ruthenium, molybdenum, or tungsten. Ruthenium, molybdenum, and tungsten have high melting points (2000°C or higher) and excellent heat resistance. The second electrode 22 containing these elements is resistant to deterioration even when subjected to heat treatment during crystallization of a laminate including the photosensitive layer 10 or heat treatment in a semiconductor process.

[0050] The second electrode 22 reflects a portion of the incident light incident from the first electrode 21 side at the interfaces with the layers in contact with the second electrode 22 (the interface between the buffer layer 14 and the second electrode 22 and the interface between the insulating layer 30 and the second electrode 22). Ruthenium, molybdenum, and tungsten have high reflectivity at these interfaces, particularly for light with a wavelength of 400 nm or more and 1500 nm or less. The light reflected by the second electrode 22 is irradiated onto the photosensitive layer 10. Because the second electrode 22 is made of a predetermined material (a metal containing at least one element selected from the group consisting of ruthenium, molybdenum, and tungsten), it reflects more incident light than if the second electrode 22 were made of a non-predetermined material. Therefore, this photodetector element irradiates a large amount of light onto the photosensitive layer 10.

[0051] The upper electrode 23 is made of a conductive material. The upper electrode 23 is made of, for example, aluminum, silver, copper, or the like. The upper electrode 23 electrically connects the first electrode 21 of the first element 1 to the first electrode 21 of the second element 2. The upper electrode 23 electrically connects the first electrode 21 of the third element 3 to the first electrode 21 of the fourth element 4.

[0052] The second element 2, the third element 3, and the fourth element 4 have a light-reflecting layer 40. In contrast, the first element 1 does not have a light-reflecting layer 40. The light-reflecting layer 40 is located so as to overlap the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4 when viewed from the Z direction. The light-reflecting layer 40 covers the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4 when viewed from the Z direction.

[0053] The light-reflecting layer 40 reflects light irradiated onto the photodetector element. The light-reflecting layer 40 is made of, for example, gold, silver, copper, or the like. The first element 1 does not have a light-reflecting layer 40, so the light to be measured is irradiated onto the photosensitive layer 10 of the first element 1. The first element 1 converts the state or change in state of the light irradiated onto the first element 1 into an electrical signal. The second element 2, the third element 3, and the fourth element 4 have a light-reflecting layer 40, so the light to be measured is not irradiated onto the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4.

[0054] The photodetector is fabricated through the processes of stacking each layer, annealing, and processing. First, the buffer layer 14, seed layer 15, third ferromagnetic layer 16, magnetic coupling layer 17, second ferromagnetic layer 12, spacer layer 13, first ferromagnetic layer 11, perpendicular magnetization induction layer 18, and cap layer 19 are stacked in this order on the second electrode 22. Each layer is formed by, for example, sputtering.

[0055] Next, the laminated film is annealed. The annealing temperature is, for example, 250°C or higher and 400°C or lower. The laminated film is then processed into a columnar laminate by photolithography and etching. The laminated body may be a cylindrical or rectangular column. For example, the minimum width of the laminated body when viewed from the Z direction is 10 nm or higher and 1000 nm or lower.

[0056] Next, an insulating layer 30 is formed to cover the side surfaces of the laminate. The insulating layer 30 may be laminated multiple times. Next, the upper surface of the cap layer 19 is exposed from the insulating layer 30 by chemical mechanical polishing, and a first electrode 21 is formed on the cap layer 19.

[0057] Next, the light-reflecting layer 40 is provided on the second element 2, the third element 3, and the fourth element 4 at a position that overlaps with the photosensitive layer 10 of each element when viewed from the Z direction. Then, an insulating layer 31 is formed so as to cover the first electrode 21 and the light-reflecting layer 40. In addition, upper electrodes 23 are formed between the first element 1 and the second element 2, and between the third element 3 and the fourth element 4, to electrically connect them. Through the above steps, the photodetector 100 is obtained.

[0058] Next, we will explain the operation of the photodetector 100. First, we will explain the operation of the first element 1. The resistance value of the first element 1 in the Z direction changes with changes in the intensity of light irradiated onto the photosensitive layer 10.

[0059] When the intensity of light irradiated onto the photosensitive layer 10 of the first element 1 changes from a first intensity to a second intensity, the resistance value in the Z direction of the first element 1 changes. The first intensity may be the case where the intensity of light irradiated onto the photosensitive layer 10 is zero.

[0060] 4 and 5 are diagrams illustrating an example of operation of the first element 1 according to the first embodiment. FIG. 4 is a diagram illustrating a first mechanism of the example of operation, and FIG. 5 is a diagram illustrating a second mechanism of the example of operation. In the upper graphs of FIGS. 4 and 5, the vertical axis represents the intensity of light irradiated onto the first ferromagnetic layer 11, and the horizontal axis represents time. In the lower graphs of FIGS. 4 and 5, the vertical axis represents the resistance value of the first element 1 in the Z direction, and the horizontal axis represents time.

[0061] First, in a state where the first ferromagnetic layer 11 is irradiated with light of a first intensity W1 (hereinafter referred to as an initial state), the magnetization M of the first ferromagnetic layer 11 is 11 and the magnetization M of the second ferromagnetic layer 12 12 are antiparallel to each other, and the resistance value in the Z direction of the first element 1 indicates a second resistance value R2. Here, the case where the intensity of light irradiated to the first ferromagnetic layer 11 is zero may be considered to be a state where light of a first intensity W1 is irradiated.

[0062] By passing a sense current Is in the Z direction through the first element 1, a voltage is generated across both ends of the first element 1 in the Z direction. The output voltage from the first element 1 is generated between the first electrode 21 and the second electrode 22.

[0063] 4, it is preferable that the sense current Is is passed from the second ferromagnetic layer 12 to the first ferromagnetic layer 11. By passing the sense current Is in this direction, the magnetization M of the first ferromagnetic layer 11 11 In contrast, the magnetization M of the second ferromagnetic layer 12 12 In the initial state, the magnetization M 11 and magnetization M 12 and tend to be antiparallel.

[0064] Next, the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the first intensity W1 to the second intensity W2. For example, when a light pulse is irradiated to the photosensitive layer 10, the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the first intensity W1 to the second intensity W2. The light at the second intensity W2 is stronger than the light at the first intensity W1.

[0065] The second intensity W2 is greater than the first intensity W1, and the magnetization M of the first ferromagnetic layer 11 11 changes from the initial state. The magnetization M of the first ferromagnetic layer 11 when the first ferromagnetic layer 11 is not irradiated with light is 11 and the magnetization M of the first ferromagnetic layer 11 irradiated with light of the second intensity W2. 11 This is different from the state of magnetization M 11 The state of the object is, for example, the tilt angle with respect to the Z direction, the size, etc.

[0066] For example, as shown in FIG. 4, when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from a first intensity W1 to a second intensity W2, the magnetization M 11 is tilted with respect to the Z direction. For example, as shown in FIG. 5, when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from a first intensity W1 to a second intensity W2, the magnetization M 11 For example, the magnitude of the magnetization M of the first ferromagnetic layer 11 11 When tilted with respect to the Z direction due to the irradiation intensity of light, the tilt angle is, for example, greater than 0° and smaller than 90°.

[0067] The magnetization M of the first ferromagnetic layer 11 is increased by irradiating the photosensitive layer 10 with a light pulse. 11 When changes from the initial state, the resistance value in the Z direction of the first element 1 indicates a first resistance value R1, and the magnitude of the output voltage from the first element 1 changes from a first value to a second value. As a result, the output from the light detection device 100 (the potential difference between the third terminal t3 and the fourth terminal t4) changes. The first resistance value R1 is smaller than the second resistance value R2. The second value is smaller than the first value. The first resistance value R1 is determined by the magnetization M 11 and magnetization M 12 The resistance value (second resistance value R2) when the magnetization M 11 and magnetization M 12 and the resistance value when they are parallel.

[0068] In the case shown in FIG. 4, the magnetization M of the first ferromagnetic layer 11 11 The magnetization M of the second ferromagnetic layer 12 is 12 Therefore, the spin transfer torque acts in the opposite direction to the magnetization M 11 is the magnetization M12 When the intensity of the light irradiated on the first ferromagnetic layer 11 changes from the second intensity to the first intensity, the magnetization M 11 is the magnetization M 12 In the case shown in FIG. 5, when the intensity of the light irradiated to the first ferromagnetic layer 11 returns to the first intensity W1, the magnetization M 11 returns to its original value, and the first element 1 returns to its initial state. In either case, the resistance value of the first element 1 in the Z direction returns to the second resistance value R2. In other words, when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the second intensity W2 to the first intensity W1, the resistance value of the first element 1 in the Z direction changes from the first resistance value R1 to the second resistance value R2.

[0069] Here, the initial state is magnetization M 11 and magnetization M 12 The example was explained using the case where the magnetization M 11 and magnetization M 12 In this case, the resistance value of the first element 1 in the Z direction is 11 The more the state of magnetization changes (for example, 11 The larger the angle change from the initial state, the larger the magnetization M 11 and magnetization M 12 When the initial state is one in which the magnetizations M and M are parallel to each other, it is preferable to flow the sense current Is from the first ferromagnetic layer 11 to the second ferromagnetic layer 12. By flowing the sense current Is in this direction, the magnetization M of the first ferromagnetic layer 11 11 In contrast, the magnetization M of the second ferromagnetic layer 12 12 In the initial state, a spin transfer torque acts in the same direction as the magnetization M 11 and magnetization M 12 and become parallel.

[0070] Although the light irradiated onto the photosensitive layer 10 has two levels of intensity, namely, the first intensity and the second intensity, the intensity of the light irradiated onto the photosensitive layer 10 may change in multiple levels or in an analog manner. In this case, the resistance value of the first element 1 changes in multiple levels or in an analog manner.

[0071] In contrast, the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4 is not irradiated with the light to be measured. Therefore, the Z-direction resistance values ​​of the second element 2, the third element 3, and the fourth element 4 do not change when irradiated with the light to be measured. On the other hand, the resistance values ​​of the second element 2, the third element 3, and the fourth element 4 change due to external disturbances. The external disturbances include, for example, temperature changes and magnetic field changes. The second element 2, the third element 3, and the fourth element 4 are in the same environment as the first element 1 and are subject to similar disturbances. For example, when a laser is irradiated onto the photodetector 100, the first element 1, the second element 2, the third element 3, and the fourth element 4 are located within a single laser spot, and therefore experience similar temperature changes.

[0072] In the photodetector 100, the first element 1, the second element 2, the third element 3, and the fourth element 4 form a bridge circuit. A , the resistance value of the second element 2 is R B , the resistance value of the third element 3 is R C , the resistance value of the fourth element 4 is R D Then, when the potential difference between the third terminal t3 and the fourth terminal t4 becomes 0, R C / R D =R A / R B When a disturbance occurs in the first element 1, the second element 2, the third element 3, and the fourth element 4, R A , R B , R C、 R D changes in the same way. In the above relational expression, the influence of disturbances on each element cancels each other out. In other words, the photodetector 100 according to this embodiment can cancel the influence of disturbances as a whole and is less susceptible to the influence of disturbances.

[0073] The output voltage from the photodetector 100 (the potential difference between the third terminal t3 and the fourth terminal t4) changes in response to changes in the intensity of light irradiating the photosensitive layer 10 of the first element 1, and the change in the intensity of the irradiated light can be converted into a change in the output voltage from the photodetector 100. In other words, the photodetector 100 can convert light into an electrical signal. For example, if the output voltage from the photodetector 100 is equal to or greater than a threshold, it is processed as a first signal (e.g., "1"), and if it is less than the threshold, it is processed as a second signal (e.g., "0").

[0074] Although an example of the present invention has been described above using the first embodiment as an example, the present invention is not limited to this embodiment.

[0075] 6 is a cross-sectional view of the vicinity of the second element 2A of a photodetector according to a first modified example of the first embodiment. The light-reflecting layer 40 of the second element 2A is located between the first electrode 21 and the photosensitive layer 10. Even in this case, the light-reflecting layer 40 reflects light incident on the photosensitive layer 10, thereby achieving the same effect as the second element 2.

[0076] 7 is a cross-sectional view of the vicinity of the second element 2B of a photodetector according to a second modified example of the first embodiment. The light-reflecting layer 40 of the second element 2B is not in direct contact with the first electrode 21, and a part of the insulating layer 31 is located between the light-reflecting layer 40 and the first electrode 21. Even in this case, the light-reflecting layer 40 reflects light incident on the photosensitive layer 10, thereby achieving the same effect as the second element 2.

[0077] "Second embodiment" 8 is a plan view of a photodetector 101 according to the second embodiment. The photodetector 101 differs from the photodetector 100 in that the photodetector 101 has a light absorbing layer 50 instead of the light reflecting layer 40. In the photodetector 101, the same components as those in the photodetector 100 are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0078] The second element 2, the third element 3, and the fourth element 4 have a light absorbing layer 50. In contrast, the first element 1 does not have a light absorbing layer 50. The light absorbing layer 50 is located so as to overlap the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4 when viewed from the Z direction. The light absorbing layer 50 covers the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4 when viewed from the Z direction.

[0079] The light absorbing layer 50 absorbs light irradiated onto the photodetector element. The light absorbing layer 50 is, for example, a blackened film of copper, aluminum, or the like, or graphite. The first element 1 does not have a light absorbing layer 50, so the light to be measured is irradiated onto the photosensitive layer 10 of the first element 1. The first element 1 converts the state or change in state of the light irradiated onto the first element 1 into an electrical signal. The second element 2, the third element 3, and the fourth element 4 have light absorbing layers 50, so the light to be measured is not irradiated onto the photosensitive layers 10 of the second element 2, the third element 3, and the fourth element 4.

[0080] The light absorbing layer 50 is preferably in contact with the upper electrode 23. The light absorbing layer 50 may absorb light and generate heat. When the light absorbing layer 50 is in contact with the upper electrode 23, the heat generated in the light absorbing layer 50 can be efficiently released to the upper electrode 23.

[0081] The photodetector 101 according to the second embodiment has the same effects as the photodetector 100 according to the first embodiment. The photodetector 101 can be modified in the same manner as the photodetector 100, and a light absorbing layer 50 may be disposed at the position of the light reflecting layer 40 in the first and second modifications.

[0082] "Third embodiment" 9 is a plan view of a photodetector 102 according to the third embodiment. The photodetector 102 differs from the photodetector 100 in that it does not have a light-reflecting layer 40 and in that it uses first electrodes 21A and 21B instead of the first electrode 21. In the photodetector 102, components similar to those in the photodetector 100 are denoted by the same reference numerals and will not be described.

[0083] The first electrode 21A is disposed on the side of the first element 1 on which incident light is incident. The incident light is irradiated onto the photosensitive layer 10 from the first electrode 21A side. The first electrode 21A is made of a conductive material. The first electrode 21A is, for example, a transparent electrode that is transparent to light in the wavelength range used. The first electrode 21A preferably transmits, for example, 80% or more of light in the wavelength range used. The first electrode 21A can be made of the same material as the first electrode 21 described above.

[0084] The first electrode 21B is disposed on the side of each of the second element 2, the third element 3, and the fourth element 4 on which incident light is incident. In each element, incident light is irradiated onto the photosensitive layer 10 from the first electrode 21B side. The first electrode 21B is a metal electrode. The first electrode 21B reflects incident light. The incident light is reflected by the first electrode 21B and does not enter the photosensitive layer 10 of the second element 2, the third element 3, and the fourth element 4. The first electrode 21B can be made of the same material as the second electrode 22 described above.

[0085] The photodetector 102 according to the third embodiment has the same effects as the photodetector 100 according to the first embodiment. The photodetector 102 according to the third embodiment does not require the provision of the light reflecting layer 40, and the number of components constituting the photodetector 102 is small.

[0086] "Fourth embodiment" Fig. 10 is a plan view of a photodetector 103 according to the fourth embodiment. Fig. 11 is a cross-sectional view of the vicinity of a first element 1 of the photodetector 103 according to the fourth embodiment. Fig. 12 is a cross-sectional view of the vicinity of a second element 2 of the photodetector 103 according to the fourth embodiment. The photodetector 103 differs from the photodetector 102 in that it has an optical waveguide 60. In the photodetector 103, components similar to those in the photodetector 102 are designated by similar reference numerals, and descriptions thereof will be omitted.

[0087] The optical waveguide 60 has a core 61 and a clad 62. The clad 62 is omitted in FIG. 10. The optical waveguide 60 totally reflects light due to the difference in refractive index between the core 61 and the clad 62. The light propagates within the core 61. A first end of the core 61 is irradiated with light from, for example, a laser diode. A second end of the core 61 is connected to the first element 1. The clad 62 surrounds the core 61.

[0088] The core 61 contains, for example, lithium niobate as a main component. Some elements of the lithium niobate may be substituted with other elements. The clad 62 is, for example, SiO2, Al2O3, MgF2, La2O3, ZnO, HfO2, MgO, Y2O3, CaF2, In2O3, etc., or a mixture thereof. The materials of the core 61 and the clad 62 are not limited to these examples. For example, the core 61 may be silicon or silicon oxide doped with germanium oxide, and the clad 62 may be silicon oxide. Alternatively, for example, the core 61 may be tantalum oxide (Ta2O5), and the clad 62 may be silicon oxide or aluminum oxide.

[0089] The light propagating through the core 61 is irradiated only onto the first element 1, and is not irradiated onto the second element 2, the third element 3, or the fourth element 4. Therefore, the light to be measured is irradiated onto the photosensitive layer 10 of the first element 1, but is not irradiated onto the photosensitive layers 10 of the second element 2, the third element 3, or the fourth element 4.

[0090] The photodetector 103 according to the fourth embodiment has the same effects as the photodetector 100 according to the first embodiment. In the photodetector 103, if it is possible to block out external light other than the light propagating through the core 61, the first electrode 21B may be replaced with a transparent electrode.

[0091] "Fifth embodiment" 13 is a plan view of a photodetector 104 according to the fifth embodiment. The photodetector 104 differs from the photodetector 100 in that it does not have an upper electrode 23, and the first electrode 21 also serves as the function of the upper electrode 23. In the photodetector 104, the same components as those in the photodetector 100 are denoted by the same reference numerals, and description thereof will be omitted.

[0092] The first electrode 21 is connected across the first element 1 and the second element 2. Similarly, the first electrode 21 is connected across the third element 3 and the fourth element 4. The first electrode 21 connected to the first element 1 and the second element 2 is connected to the third terminal t3. The first electrode 21 connected to the third element 3 and the fourth element 4 is connected to the fourth terminal t4.

[0093] The photodetector 104 according to the fifth embodiment has the same effects as the photodetector 100 according to the first embodiment. The photodetector 104 according to the fifth embodiment does not require the upper electrode 23, and the number of components constituting the photodetector 104 is small.

[0094] "Sixth embodiment" 14 is a plan view of a photodetector 105 according to the sixth embodiment. The photodetector 105 differs from the photodetector 100 in that the fourth element 4 does not have a light reflecting layer 40. In the photodetector 105, the same components as those in the photodetector 100 are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0095] The second element 2 and the third element 3 have a light-reflecting layer 40. In contrast, the first element 1 and the fourth element 4 do not have a light-reflecting layer 40. The light-reflecting layer 40 is located so as to overlap the photosensitive layer 10 of the second element 2 and the third element 3 when viewed from the Z direction. The light-reflecting layer 40 covers the photosensitive layer 10 of the second element 2 and the third element 3 when viewed from the Z direction.

[0096] Because the first element 1 and the fourth element 4 do not have a light-reflecting layer 40, the light to be measured is irradiated onto the photosensitive layer 10 of the first element 1 and the fourth element 4. The first element 1 and the fourth element 4 convert the state or change in state of the light irradiating the first element 1 and the fourth element 4 into an electrical signal. Because the second element 2 and the third element 3 have a light-reflecting layer 40, the light to be measured is not irradiated onto the photosensitive layer 10 of the second element 2 and the third element 3.

[0097] The photodetector 105 according to the sixth embodiment has the same effects as the photodetector 100 according to the first embodiment.

[0098] In the bridge circuit, the resistance of the first element 1 is R A , the resistance value of the second element 2 is R B , the resistance value of the third element 3 is R C , the resistance value of the fourth element 4 is R D Then, when the potential difference between the third terminal t3 and the fourth terminal t4 becomes 0, R C / R D =R A / R B That is, R C ×R B =R A ×R D The left side is the product of the resistance values ​​of the second element 2 and the third element 3 when no light is irradiated, and does not fluctuate due to influences other than external disturbances. When the light to be measured is irradiated onto the light detection device 105, R A and R D Therefore, the photodetector 105 can produce twice the output of the photodetector 100.

[0099] Here, an example has been shown in which the second element 2 and the third element 3 are provided with a light-reflecting layer 40, but the light-reflecting layer 40 may be replaced with a light-absorbing layer 50, as in the second embodiment. Similarly to the third embodiment, the first electrodes 21 of the second element 2 and the third element 3 may be replaced with first electrodes 21B that reflect light. Similarly to the fourth embodiment, an optical waveguide 60 may be provided, and light propagating through a core 61 may be irradiated only onto the photosensitive layers 10 of the first element 1 and the fourth element 4. Similarly to the fifth embodiment, the first electrode 21 may also serve as the upper electrode 23.

[0100] Although several embodiments and modifications have been shown and specific configurations of the photodetector have been described, the photodetector according to the present disclosure is not limited to these examples. The photodetector according to the present disclosure can be modified in various ways as long as the effects of the present disclosure are achieved. For example, the characteristic configurations of the above-described embodiments and modifications may be combined.

[0101] The photodetectors according to the above-described embodiments and modifications can be used for various purposes. The photodetector 100 described below can be substituted for the photodetectors 101, 102, 103, 104, and 105 described above.

[0102] Fig. 15 is a schematic diagram of an optical element 200 according to a first application example. The optical element 200 shown in Fig. 15 includes a waveguide element 110 and a light source 120. The waveguide element 110 includes the above-described photodetector 100 and a waveguide 111. The waveguide 111 includes an output waveguide 112 and a monitoring waveguide 113. The output waveguide 112 is a waveguide for outputting light from the light source 120 to the outside. The monitoring waveguide 113 is a waveguide for branching a portion of the light propagating through the output waveguide 112 to the photodetector 100. The monitoring waveguide 113 propagates the light to the photodetector 100.

[0103] Light source 120 is, for example, a laser light source. Light source 120 has, for example, a red laser 121, a green laser 122, and a blue laser 123. Light output from light source 120 propagates through output waveguide 112 and is output to the outside. A portion of the light output from light source 120 propagates through monitoring waveguide 113 and reaches photodetector 100.

[0104] The optical element 200 outputs laser light to the outside while monitoring the output from the light source 120 with the photodetector 100. The optical element 200 can adjust the white balance of the light output from the output waveguide 112 to the outside by adjusting the intensity of the light output from each laser.

[0105] 16 is a conceptual diagram of an optical system 300 using the optical element 200. The optical system 300 can be implemented in glasses 1000, for example.

[0106] The optical system 300 includes the optical element 200, an optical system 310, drivers 320 and 321, and a controller 330. The optical system 310 includes, for example, a collimator lens 301, a slit 302, an ND filter 303, and an optical scanning mirror 304. The optical system 310 guides the light output from the optical element 200 to an object to be illuminated (the eye in this example). The optical scanning mirror 304 is, for example, a two-axis MEMS mirror that changes the reflection direction of the laser light in the horizontal and vertical directions. The optical system 310 is an example and is not limited to this example. The driver 320 controls the output from the light source 120 of the optical element 200. The driver 321 is a control system that drives the optical scanning mirror 304. The controller 330 controls the drivers 320 and 321.

[0107] Light L output from the light source 120 of the optical element 200 G The light propagates through the optical system 310, is reflected by the lenses of the glasses 1000, and enters the eye. Here, an example is shown in which the light is reflected by the lenses of the glasses 1000, but the light may be irradiated directly onto the eye.

[0108] Red, green, and blue light L emitted from the light source 120 G displays an image. The image can be freely controlled. The output intensities of the red laser 121, the green laser 122, and the blue laser 123 can be adjusted based on the measurement results of the output from the photodetector 100, which is irradiated with the visible light output from the red laser 121, the green laser 122, and the blue laser 123, respectively.

[0109] Using this optical system 300, an image can be projected onto the glasses 1000. Furthermore, by monitoring the intensity of the projected light with the photodetector 100, the color of the image can be adjusted.

[0110] 17 is a block diagram of a transceiver 400 according to the second application example. The transceiver 400 includes a receiver 410 and a transmitter 420. The receiver 410 receives an optical signal L1, and the transmitter 420 transmits an optical signal L2.

[0111] The receiving device 410 includes, for example, a photodetector 411 and a signal processing unit 412. The photodetector 411 can be the photodetector 100 described above. In the receiving device 410, the photodetector 411 is irradiated with, for example, an optical pulse. The optical signal L1 is composed of the optical pulse. The photodetector 411 converts the optical signal L1 into an electrical signal. The signal processing unit 412 processes the electrical signal converted by the photodetector 411. The signal processing unit 412 receives the signal included in the optical signal L1 by processing the electrical signal generated from the photodetector 411. The receiving device 410 receives the signal included in the optical signal L1 based on the output signal from the photodetector 411.

[0112] The transmitting device 420 includes, for example, a light source 421, an electric signal generating element 422, and an optical modulation element 423. The light source 421 is, for example, a laser element. The light source 421 may be located outside the transmitting device 420. The electric signal generating element 422 generates an electric signal based on transmission information. The electric signal generating element 422 may be integrated with a signal conversion element of the signal processing unit 412. The optical modulation element 423 modulates the light output from the light source 421 based on the electric signal generated by the electric signal generating element 422, and outputs an optical signal L2.

[0113] Fig. 18 is a conceptual diagram of an example of a communication system. The communication system shown in Fig. 18 has two terminal devices 500. The terminal devices 500 are, for example, smartphones, tablets, personal computers, or the like.

[0114] Each of the terminal devices 500 includes a receiving device 410 and a transmitting device 420. An optical signal transmitted from the transmitting device 420 of one terminal device 500 is received by the receiving device 410 of the other terminal device 500. The light used for transmission and reception between the terminal devices 500 is, for example, visible light. The receiving device 410 includes a light detecting device 411.

[0115] 19 is a conceptual diagram of an example of a communication system. In FIG. 18, an example is shown in which the terminal devices 500 are all smartphones, but the terminal devices 500 on the transmitting side and the receiving side may be different. For example, the terminal device 500 shown in FIG. 19 is a smartphone, and the terminal device 501 is a personal computer. [Explanation of symbols]

[0116] 1 First element 2, 2A, 2B Second element 3 Third element 4 Fourth element 10 Photosensitive layer 11 First ferromagnetic layer 12 Second ferromagnetic layer 13 Spacer layer 14 Buffer layer 15 Seed layer 16 Third ferromagnetic layer 17 Magnetic coupling layer 18 Perpendicular magnetization induction layer 19 Cap Layer 21, 21A, 21B 1st electrode 22 2nd electrode 23 Upper electrode 30, 31 Insulating layer 40 Light reflective layer 50 Light absorbing layer 60 Optical waveguide 61 cores 62 Clad 100, 101, 102, 103, 104, 105 Light detection device 110 Waveguide element 111 Waveguide 112 Output waveguide 113 Monitoring Waveguide 120 light source 121 Red Laser 122 Green Laser 123 Blue Laser 200 Optical Elements 300 Optical System 301 Collimator Lens 302 Slit 303 ND filter 304 Optical scanning mirror 310 Optical system 320, 321 drivers 330 Controller 400 Transmitting and Receiving Device 410 Receiving device 411 Light detection device 412 Signal Processing Unit 420 Transmitting Device 421 Light source 422 Electrical signal generating element 423 Optical Modulator 500, 501 Terminal equipment 1000 glasses t1 First terminal t2 Second terminal t3 Third terminal t4 4th terminal

Claims

1. a first terminal, a second terminal, a third terminal, a fourth terminal, a first element, a second element, a third element, and a fourth element; the first terminal, the first element, the second element, and the second terminal form a first path; the first terminal, the third element, the fourth element, and the second terminal form a second path; the third terminal is connected between the first element and the second element; the fourth terminal is connected between the third element and the fourth element, each of the first element, the second element, the third element, and the fourth element includes a first electrode, a second electrode, and a photosensitive layer located between the first electrode and the second electrode, the photosensitive layer generating a voltage when irradiated with light; the photosensitive layer of the first element is irradiated with light to be measured; A light detection device, wherein the light sensitive layers of the second element and the third element are not irradiated with light to be measured.

2. The light detection device according to claim 1 , wherein the light to be measured is not irradiated onto the photosensitive layer of the fourth element.

3. The light detection device according to claim 1 , wherein the photosensitive layer of the fourth element is irradiated with light to be measured.

4. the first electrode of the first element is a transparent electrode; 2. The light-sensing device of claim 1, wherein the first electrodes of the second and third elements are metal electrodes.

5. the first electrode of each of the first element, the second element, the third element, and the fourth element is a transparent electrode; The light detection device according to claim 1 , wherein each of the second element and the third element further comprises a light reflecting layer at a position overlapping the photosensitive layer when viewed from the stacking direction.

6. the first electrode of each of the first element, the second element, the third element, and the fourth element is a transparent electrode; The light detection device according to claim 1 , wherein each of the second element and the third element further comprises a light absorbing layer at a position overlapping the photosensitive layer when viewed from the stacking direction.

7. further comprising an optical waveguide covering the first element, the second element, the third element, and the fourth element; the optical waveguide includes a core through which light propagates and a clad covering the core; The optical detection device according to claim 1 , wherein the light propagating through the core is irradiated onto the first element.

8. 2. The light-sensing device of claim 1, wherein the photosensitive layer comprises a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer located between the first and second ferromagnetic layers.

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