Optical detection element, receiving device, transmitting / receiving device, communication system, terminal device, and optical system

Abstract

To provide an optical detection element, a receiving device, a transmitting / receiving device, a communication system, a terminal device, and an optical system having low interfacial reflectance.SOLUTION: The optical detection element includes a photosensitive layer that generates a voltage when light is irradiated thereon, a first electrode, a second electrode, and a metal layer. The photosensitive layer is located between the first electrode and the second electrode. The metal layer is located between the first electrode and the photosensitive layer. When light having a wavelength of at least 400 nm and 800 nm or less is radiated onto the photosensitive layer, the metal layer includes at least one selected from the group consisting of Ti, Ta, Cr, Mo, W, and Pt. When light having a wavelength of at least 400 nm and 1400 nm or less is radiated onto the photosensitive layer, the metal layer includes at least one selected from the group consisting of Ti, Cr, Mo, W, and Pt. When light having a wavelength of at least 400 nm and 1500 nm or less is radiated onto the photosensitive layer, the metal layer includes at least one selected from the group consisting of Ti, Cr, W, and Pt.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photodetector, a receiving device, a transmitting / receiving device, a communication system, a terminal device, and an optical system. [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] The photodetector element converts light into an electrical signal. If the incident light is reflected before reaching the photosensitive layer of the photodetector element, not enough light can reach the photosensitive layer.

[0007] The present invention has been made in view of the above problems, and has an object to provide a photodetector, a receiving device, a transmitting / receiving device, a communication system, a terminal device, and an optical system that can suppress interface reflection. [Means for solving the problem]

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

[0009] The photodetector element according to this embodiment includes a photosensitive layer that generates a voltage when irradiated with light, a first electrode, a second electrode, and a metal layer. The photosensitive layer is located between the first electrode and the second electrode. The metal layer is located between the first electrode and the photosensitive layer. When the photosensitive layer is irradiated with light having a wavelength of 400 nm or more and 800 nm or less, the metal layer includes any one selected from the group consisting of Ti, Ta, Cr, Mo, W, and Pt. When the photosensitive layer is irradiated with light having a wavelength of 400 nm or more and 1400 nm or less, the metal layer includes any one selected from the group consisting of Ti, Cr, Mo, W, and Pt. When the photosensitive layer is irradiated with light having a wavelength of 400 nm or more and 1500 nm or less, the metal layer includes any one selected from the group consisting of Ti, Cr, W, and Pt. [Effects of the Invention]

[0010] The light-detecting element according to the above aspect has low interfacial reflection. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view of the photodetector according to the first embodiment. [Figure 2] 4 shows the results of measuring the reflectance at the interface between the first electrode and the metal layer in the photodetector element according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the relationship between the thermal conductivity of the metal layer and the light sensitivity of the photosensitive layer in the photodetector element according to the first embodiment. [Figure 4] FIG. 3 is a diagram showing the relationship between the film thickness of the metal layer and the light sensitivity of the photosensitive layer in the photodetector element according to the first embodiment. [Figure 5] 5A to 5C are diagrams illustrating an example of the operation of the light-detecting element according to the first embodiment. [Figure 6] 5A to 5C are diagrams illustrating an example of the operation of the light-detecting element according to the first embodiment. [Figure 7]FIG. 10 is a cross-sectional view of a light-detecting element according to a first modified example. [Figure 8] FIG. 1 is a schematic diagram of an optical element according to a first application example. [Figure 9] FIG. 1 is a conceptual diagram of an optical system using an optical element according to a first application example. [Figure 10] FIG. 10 is a schematic diagram of a transmitting / receiving device according to a second application example. [Figure 11] FIG. 1 is a conceptual diagram of an example of a communication system. [Figure 12] 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" Fig. 1 is a cross-sectional view of a photodetector 100 according to the first embodiment. In Fig. 1, the direction of magnetization of a ferromagnetic material in its initial state is indicated by an arrow.

[0015] The photodetector element 100 comprises a photosensitive layer 10, a first electrode 21, a second electrode 22, and a metal layer 30. The photosensitive layer 10 is located between the first electrode 21 and the second electrode 22. The metal layer 30 is located between the first electrode 21 and the photosensitive layer 10.

[0016] The photodetector element 100 may also include a buffer layer 4, a seed layer 5, a third ferromagnetic layer 6, a magnetic coupling layer 7, a perpendicular magnetization induction layer 8, a cap layer 9, and an insulating layer 90. The buffer layer 4, the seed layer 5, the third ferromagnetic layer 6, and the magnetic coupling layer 7 are located between the photosensitive layer 10 and the second electrode 22, and the perpendicular magnetization induction layer 8 and the cap layer 9 are located between the photosensitive layer 10 and the metal layer 30. The insulating layer 90 is located between the first electrode 21 and the second electrode 22, and covers the periphery of the stack including the photosensitive layer 10.

[0017] The photodetector 100 converts the state or change in state of the irradiated light into an electrical signal. In this specification, light 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. For example, the photodetector 100 (photosensitive layer 10) is irradiated with light having a wavelength of 400 nm or more and 1500 nm or less. Depending on the intended use of the photodetector 100, the photosensitive layer 10 may also be irradiated with light having a wavelength of 400 nm or more and 800 nm or less.

[0018] 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 element 100 changes in response to the change in the state of the light. The photosensitive layer 10 has, for example, a first ferromagnetic layer 1, a second ferromagnetic layer 2, and a spacer layer 3. The spacer layer 3 is located between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The photosensitive layer 10 may have other layers in addition to these.

[0019] The photosensitive layer 10 is a magnetic element containing a ferromagnetic material. For example, when the spacer layer 3 is made of an insulator, the photosensitive layer 10 has a magnetic tunnel junction (MTJ) consisting of a first ferromagnetic layer 1, a spacer layer 3, and a second ferromagnetic layer 2. 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 3 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 3, but they are also collectively called magnetoresistance effect elements. The photosensitive layer 10 has a resistance value in the Z direction (resistance value when a current flows in the Z direction) that changes in response to a relative change between the state of the magnetization M1 of the first ferromagnetic layer 1 and the state of the magnetization M2 of the second ferromagnetic layer 2.

[0020] The first ferromagnetic layer 1 is a photodetector layer whose magnetization state changes when irradiated with external light. The first ferromagnetic layer 1 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, externally irradiated light, a current flowing in the Z direction of the photosensitive layer 10, or an external magnetic field. The state of the magnetization M1 of the first ferromagnetic layer 1 changes depending on the intensity of the light irradiated to the first ferromagnetic layer 1 (light irradiated to the photosensitive layer 10).

[0021] The first ferromagnetic layer 1 includes a ferromagnetic material. The first ferromagnetic layer 1 includes at least one of magnetic elements such as Co, Fe, or Ni. The first ferromagnetic layer 1 may include elements such as B, Mg, Hf, or Gd in addition to the magnetic elements described above. The first ferromagnetic layer 1 may be, for example, an alloy including a magnetic element and a non-magnetic element. The first ferromagnetic layer 1 may be composed of multiple layers. The first ferromagnetic layer 1 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 1 may exhibit ferrimagnetic properties. On the other hand, the first ferromagnetic layer 1 may exhibit ferromagnetic properties that are not ferrimagnetic. For example, a CoFeB alloy exhibits ferromagnetic properties that are not ferrimagnetic.

[0022] The first ferromagnetic layer 1 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).

[0023] The 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 is preferably, for example, 1 nm or more and 2 nm or less. When the first ferromagnetic layer 1 is a perpendicular magnetization film, if the thickness of the first ferromagnetic layer 1 is thin, the perpendicular magnetic anisotropy applied effect from the layers above and below the first ferromagnetic layer 1 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is increased. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high, the force that causes the magnetization M1 to return to the Z direction is strengthened. On the other hand, if the thickness of the first ferromagnetic layer 1 is thick, the perpendicular magnetic anisotropy applied effect 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.

[0024] As the thickness of the first ferromagnetic layer 1 decreases, its volume as a ferromagnetic material decreases, and as it increases, its volume as a ferromagnetic material increases. The responsiveness of the magnetization M1 of the first ferromagnetic layer 1 when external energy is applied is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and volume (V) of the first ferromagnetic layer 1. In other words, as the product of the magnetic anisotropy and volume of the first ferromagnetic layer 1 decreases, its responsiveness to light increases. From this perspective, in order to enhance its responsiveness to light, it is preferable to reduce the volume of the first ferromagnetic layer 1 after appropriately designing the magnetic anisotropy of the first ferromagnetic layer 1.

[0025] If the thickness of the first ferromagnetic layer 1 is greater than 2 nm, an insertion layer made of, for example, Mo or W may be provided within the first ferromagnetic layer 1. That is, the first ferromagnetic layer 1 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 1. The thickness of the insertion layer is, for example, 0.1 nm to 1.0 nm.

[0026] The second ferromagnetic layer 2 is a magnetization fixed layer. The magnetization fixed layer is a layer made of a magnetic material in which the state of magnetization M2 is less likely to change than the magnetization free layer when a predetermined external energy is applied. 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 2 is, for example, greater than the coercive force of the first ferromagnetic layer 1. The second ferromagnetic layer 2 has an easy axis of magnetization in the same direction as the first ferromagnetic layer 1, for example. The second ferromagnetic layer 2 may be an in-plane magnetization film or a perpendicular magnetization film.

[0027] The material constituting the second ferromagnetic layer 2 is, for example, the same as that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be, 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 2 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.

[0028] The magnetization M2 of the second ferromagnetic layer 2 may be fixed, for example, by magnetic coupling with the magnetization M6 of the third ferromagnetic layer 6. In this case, the combination of the second ferromagnetic layer 2, the magnetic coupling layer 7, and the third ferromagnetic layer 6 may be referred to as a magnetization fixed layer. Details of the magnetic coupling layer 7 and the third ferromagnetic layer 6 will be described later.

[0029] The spacer layer 3 is a layer disposed between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The spacer layer 3 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 3 is, for example, a non-magnetic layer. The thickness of the spacer layer 3 can be adjusted depending on the orientation directions of the magnetizations of the first ferromagnetic layer 1 and the second ferromagnetic layer 2 in the initial state, which will be described later.

[0030] When the spacer layer 3 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 3. These insulating materials may also contain elements such as Al, B, Si, and Mg, or magnetic elements such as Co, Fe, and Ni. A high magnetoresistance ratio can be obtained by adjusting the thickness of the spacer layer 3 so that a high TMR effect is exhibited between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. To efficiently utilize the TMR effect, the thickness of the spacer layer 3 may be approximately 0.5 to 5.0 nm, or approximately 1.0 to 2.5 nm.

[0031] When the spacer layer 3 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 3 may be about 0.5 to 5.0 nm, or about 2.0 to 3.0 nm.

[0032] When the spacer layer 3 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 3 may be about 1.0 to 4.0 nm.

[0033] When a layer including current-carrying points formed by a conductor in a nonmagnetic insulator is used as the spacer layer 3, 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 made of a magnetic element such as Co, Fe, or Ni. In this case, the thickness of the spacer layer 3 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.

[0034] The third ferromagnetic layer 6 is magnetically coupled to, for example, the second ferromagnetic layer 2. The magnetic coupling is, for example, antiferromagnetic coupling, and occurs due to RKKY interaction. The material constituting the third ferromagnetic layer 6 is, for example, the same as that of the first ferromagnetic layer 1.

[0035] The magnetic coupling layer 7 is located between the second ferromagnetic layer 2 and the third ferromagnetic layer 6. The magnetic coupling layer 7 is made of, for example, Ru, Ir, or the like.

[0036] The buffer layer 4 is a layer that reduces lattice mismatch between different crystals. The buffer layer 4 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 4 is, for example, Ta (element), a NiCr alloy, TaN (tantalum nitride), or CuN (copper nitride). The buffer layer 4 has a thickness of, for example, 1 nm or more and 5 nm or less. The buffer layer 4 is, for example, amorphous. The buffer layer 4 is, for example, located between the seed layer 5 and the second electrode 22 and in contact with the second electrode 22. The buffer layer 4 prevents the crystal structure of the second electrode 22 from affecting the crystal structure of the photosensitive layer 10.

[0037] The seed layer 5 improves the crystallinity of layers stacked on the seed layer 5. The seed layer 5 is located, for example, between the buffer layer 4 and the third ferromagnetic layer 6 and on the buffer layer 4. The seed layer 5 is made of, for example, Pt, Ru, Zr, or NiFeCr. The thickness of the seed layer 5 is, for example, 1 nm or more and 5 nm or less.

[0038] The cap layer 9 is located between the first ferromagnetic layer 1 and the first electrode 21. The cap layer 9 may include a perpendicular magnetization induction layer 8 stacked on the first ferromagnetic layer 1 and in contact with the first ferromagnetic layer 1. The cap layer 9 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 9 is, for example, 10 nm or less so that the first ferromagnetic layer 1 is irradiated with sufficient light.

[0039] The perpendicular magnetization induction layer 8 induces perpendicular magnetic anisotropy in the first ferromagnetic layer 1. The perpendicular magnetization induction layer 8 is made of, for example, magnesium oxide, W, Ta, or Mo. When the perpendicular magnetization induction layer 8 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 8 is, for example, 0.5 nm or more and 5.0 nm or less.

[0040] The insulating layer 90 is made of, for example, an oxide, nitride, or oxynitride of Si, Al, or Mg. The insulating layer 90 is made of, for example, silicon oxide (SiOx ), silicon nitride (SiN x ), silicon carbide (SiC), chromium nitride, silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al2O3), zirconium oxide (ZrO x ) etc.

[0041] The first electrode 21 is disposed on the side of the photodetector element 100 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 film on the surface irradiated with light.

[0042] 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.

[0043] 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.

[0044] 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 4 and the second electrode 22 and the interface between the insulating layer 90 and the second electrode 22). Ruthenium, molybdenum, and tungsten have high light reflectance at these interfaces, particularly for light with a wavelength of 400 nm or more and 1500 nm or less at these interfaces. 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, the photodetector element 100 irradiates a large amount of light onto the photosensitive layer 10.

[0045] The metal layer 30 is between the photosensitive layer 10 and the first electrode 21. The metal layer 30 is, for example, between the cap layer 9 and the first electrode 21.

[0046] When the photosensitive layer 10 is irradiated with light having a wavelength of 400 nm or more and 800 nm or less, the metal layer 30 contains any one selected from the group consisting of Ti, Ta, Cr, Mo, W, and Pt. When the photosensitive layer 10 is irradiated with light having a wavelength of 400 nm or more and 1400 nm or less, the metal layer 30 contains any one selected from the group consisting of Ti, Cr, Mo, W, and Pt. When the photosensitive layer 10 is irradiated with light having a wavelength of 400 nm or more and 1500 nm or less, the metal layer 30 contains any one selected from the group consisting of Ti, Cr, W, and Pt.

[0047] 2 shows the measurement results of the reflectance at the interface between the first electrode 21 and the lower layer in the photodetector element according to the first embodiment. Comparative Example 1 shows the measurement results of the reflectance at the interface between the first electrode 21 and the photosensitive layer 10 when the metal layer 30 is not provided between the first electrode 21 and the photosensitive layer 10. Other examples include cases where any of Ti, Ta, Cr, Mo, W, and Pt is used as the metal layer 30. The photosensitive layer 10 mainly contains Co.

[0048] As shown in FIG. 2 , when the photosensitive layer 10 is irradiated with light having a wavelength of 400 nm or more and 800 nm or less, reflection at the interface between the first electrode 21 and the photosensitive layer 10 can be reduced by providing a metal layer 30 containing one selected from the group consisting of Ti, Ta, Cr, Mo, W, and Pt between the first electrode 21 and the photosensitive layer 10. When the photosensitive layer 10 is irradiated with light having a wavelength of 400 nm or more and 1400 nm or less, reflection at the interface between the first electrode 21 and the photosensitive layer 10 can be reduced by providing a metal layer 30 containing one selected from the group consisting of Ti, Cr, Mo, W, and Pt between the first electrode 21 and the photosensitive layer 10. When the photosensitive layer 10 is irradiated with light having a wavelength of 400 nm or more and 1500 nm or less, reflection at the interface between the first electrode 21 and the photosensitive layer 10 can be reduced by providing a metal layer 30 containing one selected from the group consisting of Ti, Cr, W, and Pt between the first electrode 21 and the photosensitive layer 10. Reducing reflection at these interfaces increases the amount of light irradiating the photosensitive layer 10, improving the photodetection capability of the photodetector element 100.

[0049] Furthermore, when the first electrode 21 is made of ITO, IZO, ZnO, or IGZO, the metal layer 30 preferably contains any one selected from the group consisting of Ti, Ta, Cr, Mo, W, and Pt. When the above configuration is satisfied, the complex refractive indices of the first electrode 21 and the metal layer 30 can be made close to each other, and reflection between the first electrode 21 and the metal layer 30 can be particularly suppressed.

[0050] Furthermore, when the cap layer 9 is made of Ru, it is preferable that the metal layer 30 contains any one selected from the group consisting of Ru and Ti, and when the cap layer 9 is made of Ta, it is preferable that the metal layer 30 contains any one selected from the group consisting of Ta, Cr, Mo, W, and Pt. When the cap layer 9 and the metal layer 30 satisfy these combinations, reflection between the cap layer 9 and the metal layer 30 can be suppressed.

[0051] The thermal conductivity of the metal layer 30 is preferably 60 W / mK or less. FIG. 3 shows the relationship between the thermal conductivity of the metal layer 30 and the photosensitivity of the photosensitive layer 10 in the photodetector element 100 according to the first embodiment. The horizontal axis of FIG. 3 represents the thermal conductivity of the metal layer 30, and the vertical axis of FIG. 3 represents the photosensitivity of each example normalized by the photosensitivity of the photosensitive layer 10 in Comparative Example 1. Comparative Example 1 represents the photosensitivity of the photosensitive layer 10 when no metal layer 30 is provided between the first electrode 21 and the photosensitive layer 10. The other examples use one of Ti, Cr, Mo, W, Ru, and Cu as the metal layer 30. The photosensitivity is measured when irradiated with a sine wave laser beam having a wavelength of 850 nm, a peak power of 4.8 mW, and a frequency of 1 GHz. The thickness of the metal layer was 200 Å.

[0052] 3, it can be seen that a low thermal conductivity of the metal layer 30 increases the light sensitivity of the photosensitive layer 10. This is thought to be because the metal layer 30 functions as a heat reservoir, reducing heat diffusion from the photosensitive layer 10. When the temperature of the photosensitive layer 10 is high, the magnetization M1 of the first ferromagnetic layer 1 moves more easily, increasing the sensitivity of the photodetector element 100 to light. The metal layer 30 is preferably made of Ti or Cr.

[0053] Fig. 4 is a diagram showing the relationship between the film thickness of the metal layer 30 and the light sensitivity of the photosensitive layer 10 in the photodetector element 100 according to the first embodiment. Fig. 4 shows the light sensitivity when irradiated with a sine wave laser having a wavelength of 850 nm, a peak power of 4.8 mW, and a frequency of 1 GHz, and the film thickness of the metal layer 30 made of Ti was changed.

[0054] 4, the thickness of the metal layer 30 is preferably 100 Å to 1000 Å, more preferably 200 Å to 600 Å, and even more preferably 300 Å to 500 Å. If the thickness of the metal layer 30 is too thick, heat is likely to diffuse from the metal layer 30 to the surrounding insulating layer 90, reducing the amount of heat propagating from the metal layer 30 to the photosensitive layer 10.

[0055] The photodetector element 100 is fabricated through a process of stacking each layer, an annealing process, and a processing process. First, the buffer layer 4, seed layer 5, third ferromagnetic layer 6, magnetic coupling layer 7, second ferromagnetic layer 2, spacer layer 3, first ferromagnetic layer 1, perpendicular magnetization induction layer 8, cap layer 9, and metal layer 30 are stacked in this order on the second electrode 22. Each layer is formed by, for example, sputtering.

[0056] 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.

[0057] Next, an insulating layer 90 is formed to cover the side surfaces of the laminate. The insulating layer 90 may be laminated multiple times. Next, the upper surface of the metal layer 30 is exposed from the insulating layer 90 by chemical mechanical polishing, and the first electrode 21 is formed on the metal layer 30. Through the above steps, the photodetector element 100 is obtained.

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

[0059] When the intensity of light irradiating the photosensitive layer 10 of the photodetector element 100 changes from a first intensity to a second intensity, the resistance value in the Z direction of the photodetector element 100 changes. The first intensity may be when the intensity of light irradiating the photosensitive layer 10 is zero. When the resistance value in the Z direction of the photodetector element 100 changes, the output voltage from the photodetector element 100 changes.

[0060] 5 and 6 are diagrams illustrating an example of operation of the photodetector 100 according to the first embodiment. FIG. 5 is a diagram illustrating a first mechanism of the example of operation, and FIG. 6 is a diagram illustrating a second mechanism of the example of operation. In the upper graphs of FIGS. 5 and 6, the vertical axis represents the intensity of light irradiated onto the first ferromagnetic layer 1, and the horizontal axis represents time. In the lower graphs of FIGS. 5 and 6, the vertical axis represents the resistance value of the photodetector 100 in the Z direction, and the horizontal axis represents time.

[0061] First, in a state where the first ferromagnetic layer 1 is irradiated with light of a first intensity W1 (hereinafter referred to as the initial state), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are antiparallel to each other, and the resistance value in the Z direction of the photodetector element 100 exhibits a second resistance value R2. Here, the case where the intensity of the light irradiated to the first ferromagnetic layer 1 is zero may be considered to be the state where light of the first intensity W1 is irradiated.

[0062] By passing a sense current Is through the photodetector element 100 in the Z direction, a voltage is generated across both ends of the photodetector element 100 in the Z direction. An output voltage from the photodetector element 100 is generated between the first electrode 21 and the second electrode 22.

[0063] 5, it is preferable to flow the sense current Is from the second ferromagnetic layer 2 toward the first ferromagnetic layer 1. By flowing the sense current Is in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the opposite direction to the magnetization M2 of the second ferromagnetic layer 2, and the magnetizations M1 and M2 tend to be antiparallel to each other in the initial state.

[0064] Next, the intensity of the light irradiated to the first ferromagnetic layer 1 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 1 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 M1 of the first ferromagnetic layer 1 changes from its initial state. The state of the magnetization M1 of the first ferromagnetic layer 1 when no light is irradiated onto the first ferromagnetic layer 1 is different from the state of the magnetization M1 of the first ferromagnetic layer 1 when irradiated with light of the second intensity W2. The state of the magnetization M1 refers to, for example, the tilt angle or magnitude with respect to the Z direction.

[0066] For example, as shown in Fig. 5, when the intensity of light irradiated to the first ferromagnetic layer 1 changes from a first intensity W1 to a second intensity W2, the magnetization M1 tilts with respect to the Z direction. Also, for example, as shown in Fig. 6, when the intensity of light irradiated to the first ferromagnetic layer 1 changes from the first intensity W1 to a second intensity W2, the magnitude of the magnetization M1 decreases. For example, when the magnetization M1 of the first ferromagnetic layer 1 tilts 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] When the magnetization M1 of the first ferromagnetic layer 1 changes from its initial state due to irradiation of the photosensitive layer 10 with a light pulse, the resistance value in the Z direction of the photodetector element 100 exhibits a first resistance value R1, and the magnitude of the output voltage from the photodetector element 100 changes from a first value to a second value. As a result, the output from the photodetector element 100 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 between the resistance value (second resistance value R2) when the magnetization M1 and the magnetization M2 are antiparallel and the resistance value when the magnetization M1 and the magnetization M2 are parallel.

[0068] In the case shown in FIG. 5, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the opposite direction to the magnetization M2 of the second ferromagnetic layer 2. Therefore, the magnetization M1 attempts to return to an antiparallel state with respect to the magnetization M2. When the intensity of the light irradiating the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the magnetization M1 returns to an antiparallel state with respect to the magnetization M2. In the case shown in FIG. 6, when the intensity of the light irradiating the first ferromagnetic layer 1 returns to the first intensity W1, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 returns to its original value, and the photodetector element 100 returns to its initial state. In either case, the resistance value in the Z direction of the photodetector element 100 returns to the second resistance value R2. That is, when the intensity of the light irradiating the first ferromagnetic layer 1 changes from the second intensity W2 to the first intensity W1, the resistance value in the Z direction of the photodetector element 100 changes from the first resistance value R1 to the second resistance value R2.

[0069] The output voltage from the photodetector element 100 changes in response to changes in the intensity of light irradiated onto the photosensitive layer 10, and the change in the intensity of the irradiated light can be converted into a change in the output voltage from the photodetector element 100. In other words, the photodetector element 100 can convert light into an electrical signal. For example, if the output voltage from the photodetector element 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").

[0070] Here, the case where the magnetization M1 and the magnetization M2 are antiparallel in the initial state has been described as an example, but the magnetization M1 and the magnetization M2 may be parallel in the initial state. In this case, the resistance value in the Z direction of the photodetector element 100 increases as the state of the magnetization M1 changes (for example, as the angle of the magnetization M1 from the initial state increases). If the initial state is one in which the magnetization M1 and the magnetization M2 are parallel, it is preferable to flow the sense current Is from the first ferromagnetic layer 1 to the second ferromagnetic layer 2. By flowing the sense current Is in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the same direction as the magnetization M2 of the second ferromagnetic layer 2, and the magnetization M1 and the magnetization M2 become parallel in the initial state.

[0071] Although the example described here is one in which 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 output voltage from the photodetector element 100 changes in multiple levels or in an analog manner.

[0072] The photodetector 100 according to the first embodiment can convert light irradiated onto the photosensitive layer 10 into an output voltage from the photodetector element 100, thereby converting the light into an electrical signal. The photodetector element 100 according to the first embodiment has a metal layer 30 between the first electrode 21 and the photosensitive layer 10, thereby reducing interface reflection and improving light detection capability.

[0073] 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.

[0074] For example, Fig. 7 is a cross-sectional view of a photodetector 101 according to a first modified example. Fig. 7 differs from the photodetector 100 in that the shape of the metal layer 31 is different from that of the metal layer 30. The metal layer 31 extends outward from the photosensitive layer 10 when viewed in the Z direction. The photodetector 101 according to the first modified example has the same effects as the photodetector 100.

[0075] The photodetector 100 according to the above-described embodiment and modifications can be used for various purposes.

[0076] FIG. 8 is a schematic diagram of an optical element 200 according to a first application example. The optical element 200 shown in FIG. 8 includes a waveguide element 110 and a light source 120. The waveguide element 110 includes the above-described photodetector element 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 element 100. The monitoring waveguide 113 propagates light to the photodetector element 100.

[0077] 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 element 100.

[0078] The optical element 200 outputs laser light to the outside while monitoring the output from the light source 120 with the photodetector element 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.

[0079] 9 is a conceptual diagram of an optical system 300 using the optical element 200. The optical system 300 can be implemented in, for example, glasses 1000.

[0080] 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.

[0081] 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.

[0082] Red, green, and blue light L emitted from the light source 120G 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 element 100 irradiated with the visible light output from the red laser 121, the green laser 122, and the blue laser 123, respectively.

[0083] 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 element 100, the color of the image can be adjusted.

[0084] 10 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.

[0085] The receiving device 410 includes, for example, a photodetector 411 and a signal processing unit 412. The photodetector 411 can be the photodetector element 100 described above. In the receiving device 410, the photodetector element 100 of 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.

[0086] 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.

[0087] Fig. 11 is a conceptual diagram of an example of a communication system. The communication system shown in Fig. 11 has two terminal devices 500. The terminal devices 500 are, for example, smartphones, tablets, personal computers, etc.

[0088] 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.

[0089] 12 is a conceptual diagram of an example of a communication system. In FIG. 11, 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. 12 is a smartphone, and the terminal device 501 is a personal computer. [Explanation of symbols]

[0090] 1 First ferromagnetic layer 2 Second ferromagnetic layer 3 Spacer layer 4. Buffer layer 5 Seed layer 6 Third ferromagnetic layer 7 Magnetic coupling layer 8 Perpendicular magnetization induction layer 9 Cap Layer 10 Photosensitive layer 21 1st electrode 22 2nd electrode 30 metal layer 100, 101 Photodetector

Claims

1. The device includes a photosensitive layer that generates a voltage when irradiated with light, a first electrode, a second electrode, and a metal layer; the photosensitive layer is located between the first electrode and the second electrode; the metal layer is located between the first electrode and the photosensitive layer; When the photosensitive layer is irradiated with light having a wavelength of 400 nm or more and 800 nm or less, the metal layer contains any one selected from the group consisting of Ti, Ta, Cr, Mo, W, and Pt, When the photosensitive layer is irradiated with light having a wavelength of 400 nm or more and 1400 nm or less, the metal layer contains any one selected from the group consisting of Ti, Cr, Mo, W, and Pt, A photodetector element, wherein when the photosensitive layer is irradiated with light having a wavelength of 400 nm or more and 1500 nm or less, the metal layer contains any one selected from the group consisting of Ti, Cr, W, and Pt.

2. The light-sensing element of claim 1 , wherein the first electrode is a transparent electrode.

3. The photo-sensing element of claim 1 , wherein the photosensitive layer comprises a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer located between the first ferromagnetic layer and the second ferromagnetic layer.

4. The photo-sensing element according to claim 1 , wherein the thermal conductivity of the metal layer is 60 W / mK or less.

5. The photo-sensing element according to claim 1 , wherein the thickness of the metal layer is between 100 Å and 1000 Å.

6. A receiving device comprising a photodetector element according to claim 1.

7. A transmitting / receiving device comprising the receiving device according to claim 6.

8. A communication system comprising a receiving device according to claim 6.

9. A terminal device comprising the receiving device according to claim 6.

10. An optical system comprising a light-sensing element according to claim 1 .

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