Receiving device, transmitting / receiving device, communication system, portable terminal device, and photodetector element

Abstract

To provide a novel receiving device, a communication system, a sending-receiving device, a communication system, and an optical detection element that allow rapid communication.SOLUTION: A receiving device has a magnetic element including: a first ferromagnetic layer; a second ferromagnetic layer; and a space layer between the first ferromagnetic layer and the second ferromagnetic layer. Light containing a light signal with light intensity change is applied to the first ferromagnetic layer and the light receiving device receives the light signal on the basis of an output voltage from the magnetic element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a receiving device, a transmitting / receiving device, a communication system, a mobile terminal device, and a light detecting element. [Background technology]

[0002] With the spread of the Internet, communication traffic has increased dramatically, and the importance of optical communication has become extremely high. Optical communication is a communication method that converts electrical signals into optical signals and transmits and receives them.

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-292107 A Summary of the Invention [Problem to be solved by the invention]

[0005] With the development of information and communication technology, there is a demand for even faster communication speeds, and in optical communication, there is a demand for higher signal modulation frequencies to achieve high-speed communication. The semiconductor photodiode shown in Patent Document 1 has a problem in that the receiving sensitivity drops significantly as the frequency increases, and a new breakthrough is required for further development.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a new receiving device, receiving system, transmitting / receiving device, communication system, and photodetector element that enable high-speed communication. [Means for solving the problem]

[0007] In order to solve the above problems, the following means are provided.

[0008] (1) A receiving device according to a first aspect includes a magnetic element having a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, in which light including an optical signal having a change in optical intensity is irradiated to the first ferromagnetic layer, and the optical signal is received based on an output voltage from the magnetic element.

[0009] (2) The receiving device according to the above aspect may be configured such that the output voltage from the magnetic element changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer.

[0010] (3) In the receiving device of the above aspect, the angle between the magnetization direction of the first ferromagnetic layer when the first ferromagnetic layer is not irradiated with the light and the magnetization direction of the first ferromagnetic layer when the first ferromagnetic layer is irradiated with the light may be greater than 0° and less than 90°.

[0011] (4) In the receiving device of the above aspect, the optical signal has at least two levels of intensity, and the magnitude of the output voltage from the magnetic element shows a first value when the intensity of the light irradiated to the first ferromagnetic layer is a first intensity, and shows a second value when the intensity of the light irradiated to the first ferromagnetic layer is a second intensity, and under the condition that the second intensity is greater than the first intensity, if the second value is greater than the first value, a current may be passed from the first ferromagnetic layer to the second ferromagnetic layer, and if the second value is smaller than the first value, a current may be passed from the second ferromagnetic layer to the first ferromagnetic layer.

[0012] (5) The receiving device of the above aspect may further include a hard bias layer that applies a bias magnetic field to the first ferromagnetic layer, the hard bias layer being positioned so as to overlap the first ferromagnetic layer when viewed from any direction perpendicular to the stacking direction of the magnetic element, and the magnetization direction of the hard bias layer may be opposite to the magnetization direction of the first ferromagnetic layer when the light is not irradiated.

[0013] (6) In the receiving device of the above aspect, the magnetic element may further include a first electrode connected to the first ferromagnetic layer and a second electrode connected to the second ferromagnetic layer, and the first electrode may be transparent to light in the wavelength range used by the optical signal.

[0014] (7) The receiving device according to the above aspect may further include a soft magnetic body, which may cover at least a portion of an outer periphery of the magnetic element from the outside in a plan view in a stacking direction of the magnetic element.

[0015] (8) In the receiving device of the above aspect, the soft magnetic body may also be located above and below the magnetic element in the stacking direction, and the soft magnetic body located above and below the magnetic element on the side of the first ferromagnetic layer may have an opening.

[0016] (9) In the receiving device according to the above aspect, the opening may have a mesh-shaped magnetic net connected to the soft magnetic material.

[0017] (10) In the receiving device according to the above aspect, when the output voltage from the magnetic element is equal to or greater than a threshold, it may be processed as a first signal, and when it is less than the threshold, it may be processed as a second signal.

[0018] (11) In the receiving device according to the above aspect, a change in the output voltage from the magnetic element within a predetermined time may be processed as a first signal, and a failure of the output voltage from the magnetic element to change within a predetermined time may be processed as a second signal.

[0019] (12) The receiving device according to the above aspect may further include an integrated circuit, wherein the magnetic element and the integrated circuit are formed on the same substrate via an interlayer insulating film, and the integrated circuit and the magnetic element are connected via a through-wire that penetrates the interlayer insulating film.

[0020] (13) A transmitting / receiving device according to a second aspect includes the receiving device according to the above aspect and a transmitting device that transmits an optical signal.

[0021] (14) A communication system according to a third aspect includes a plurality of transmitting / receiving devices according to the above aspect.

[0022] (15) A mobile terminal device according to a fourth aspect includes the receiving device according to the above aspect.

[0023] (16) A photodetector according to a fifth aspect includes a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, and an output voltage changes in response to a change in the intensity of light irradiated to the first ferromagnetic layer.

[0024] (17) In the photodetector element of the above aspect, an angle between the magnetization direction of the first ferromagnetic layer when the first ferromagnetic layer is not irradiated with light and the magnetization direction of the first ferromagnetic layer when the first ferromagnetic layer is irradiated with light may be greater than 0° and less than 90°.

[0025] (18) The photodetector element according to the above aspect may be configured such that an optical signal having at least two levels of intensity is irradiated, the magnitude of the output voltage shows a first value when the intensity of the light irradiated to the first ferromagnetic layer is a first intensity, and the magnitude of the output voltage shows a second value when the intensity of the light irradiated to the first ferromagnetic layer is a second intensity, and under the condition that the second intensity is greater than the first intensity, a current flows from the first ferromagnetic layer to the second ferromagnetic layer when the second value is greater than the first value, and a current flows from the second ferromagnetic layer to the first ferromagnetic layer when the second value is smaller than the first value. Effect of the Invention

[0026] The receiving device, the transmitting / receiving device, the communication system, the mobile terminal device, and the photodetector element according to the above aspects are novel and will lead to new breakthroughs. In addition, the receiving device, the transmitting / receiving device, the communication system, the mobile terminal device, and the photodetector element according to the above aspects are capable of high-speed communication. [Brief description of the drawings]

[0027] [Figure 1] 1 is a conceptual diagram of a communication system according to a first embodiment. [Diagram 2] 1 is a block diagram of a transmission / reception device according to a first embodiment. [Diagram 3] 1 is a circuit diagram of a transmission / reception device according to a first embodiment. [Figure 4] 1 is a cross-sectional view of a receiving device according to a first embodiment. [Diagram 5] 1 is a cross-sectional view of a light-detecting element according to a first embodiment. [Figure 6] 4A to 4C are schematic diagrams for explaining the operation of a first pattern of the light-detecting element according to the first embodiment by a first mechanism. [Figure 7] 5A to 5C are schematic diagrams for explaining the operation of the first pattern of the light-detecting element according to the first embodiment by a second mechanism. [Figure 8] 5A to 5C are schematic diagrams for explaining the operation of the second pattern of the light-detecting element according to the first embodiment by a first mechanism. [Figure 9] 6A to 6C are schematic diagrams for explaining the operation of the second pattern of the light-detecting element according to the first embodiment by a second mechanism. [Figure 10] 4A to 4C are schematic diagrams for explaining the operation of the photodetector according to the first embodiment by a first mechanism when the photodetector is used to output multiple values. [Figure 11] 6A to 6C are schematic diagrams for explaining the operation of the photodetector according to the first embodiment by a second mechanism when the photodetector is used to output multiple values. [Figure 12]3A to 3C are schematic diagrams illustrating behavior of the light detection element in the first embodiment when an abnormality occurs in the light detection element. [Figure 13] FIG. 13 is a diagram showing simulation results of sensitivity in an example and comparative example 1. [Figure 14] FIG. 13 is a diagram showing simulation results of sensitivity in an example and comparative example 2. [Figure 15] FIG. 11 is a circuit diagram of a transmission / reception device according to a first modified example. [Figure 16] 11 is a cross-sectional view of a light-detecting element according to a second modified example taken along a plane along the z direction. FIG. [Figure 17] 13 is a cross-sectional view of a photodetector according to a second modified example and its periphery taken along an xy plane passing through a first ferromagnetic layer 1. FIG. [Figure 18] 13 is a cross-sectional view of a light-detecting element according to a third modified example taken along a plane along the z-direction. FIG. [Figure 19] FIG. 11 is a cross-sectional view of a receiving device according to a fourth modified example taken along a plane along the z direction. [Figure 20] FIG. 13 is a plan view of a receiving device according to a fourth modified example, seen from the z direction. [Figure 21] FIG. 11 is a cross-sectional view of a receiving device according to a fifth modified example taken along a plane along the z direction. [Figure 22] FIG. 13 is a plan view of a receiving device according to a fifth modified example, seen from the z direction. [Figure 23] FIG. 13 is a cross-sectional view of a receiving device according to a sixth modified example. [Figure 24] FIG. 11 is a diagram for explaining the operation of the receiving device according to the second embodiment. [Diagram 25] FIG. 1 is a conceptual diagram of another example of a communication system. [Figure 26] FIG. 1 is a conceptual diagram of another example of a communication system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 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 parts in an enlarged scale for the sake of convenience in order to make the characteristics 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, and may be appropriately modified and implemented within the scope of the effects of the present invention.

[0029] The directions are defined as follows. The stacking direction of the photodetector element 10 is the z direction, one direction in a plane perpendicular to the z direction is the x direction, and a direction perpendicular to the x and z directions is the y direction. The z direction is an example of a stacking direction. Hereinafter, the +z direction may be expressed as "up" and the -z direction as "down". The +z direction is the direction from the substrate Sb to the photodetector element 10. Up and down do not necessarily coincide with the direction in which gravity is applied.

[0030] "First embodiment" FIG. 1 is a conceptual diagram of a communication system 1000 according to the first embodiment. The communication system 1000 shown in FIG. 1 includes a plurality of transmission / reception devices 300 and a fiber FB connecting the transmission / reception devices 300 to each other. The communication system 1000 can be used for short-distance or medium-distance communication such as within a data center or between data centers, or for long-distance communication such as between cities. The transmission / reception devices 300 are installed, for example, in a data center or in a base station or backbone station of a long-distance communication network. The fiber FB connects, for example, between data centers. The communication system 1000 performs communication between the transmission / reception devices 300, for example, via the fiber FB. The communication system 1000 may perform communication between the transmission / reception devices 300 wirelessly without using the fiber FB.

[0031] 2 is a block diagram of a transmission / reception device 300 according to the first embodiment. The transmission / reception device 300 includes a reception device 100 and a transmission device 200. The reception device 100 receives an optical signal L1, and the transmission device 200 transmits an optical signal L2. 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.

[0032] The receiving device 100 includes, for example, a photodetector element 10 and a signal processor 11. The photodetector element 10 converts the optical signal L1 into an electrical signal. Details of the photodetector element 10 will be described later. The signal processor 11 processes the electrical signal converted by the photodetector element 10. The signal processor 11 receives a signal included in the optical signal L1 by processing the electrical signal generated by the photodetector element 10.

[0033] The transmitting device 200 includes, for example, a light source 201, an electric signal generating element 202, and an optical modulation element 203. The light source 201 is, for example, a laser element. The light source 201 may be located outside the transmitting device 200. The electric signal generating element 202 generates an electric signal based on transmission information. The electric signal generating element 202 may be integrated with a signal conversion element of the signal processing unit 11. The optical modulation element 203 modulates the light output from the light source 201 based on the electric signal generated by the electric signal generating element 202, and outputs an optical signal L2.

[0034] Fig. 3 is a circuit diagram of a transmission / reception device 300 according to the first embodiment. In Fig. 3, the signal processing unit 11 is omitted.

[0035] The receiving device 100 includes, for example, a photodetector element 10, a first electrode 15, a second electrode 16, and an input terminal P in and output terminal P out and the reference potential terminal P G The first electrode 15 and the second electrode 16 sandwich the light detection element 10 in the stacking direction. The first electrode 15 is, for example, an electrode on the side that is irradiated with light including the optical signal L1.

[0036] The first electrode 15 is connected to, for example, an input terminal Pin and an output terminal Pout. The second electrode 16 is connected to, for example, a reference potential terminal PG. The input terminal Pin is connected to a power source PS. The power source PS may be external to the receiving device 100. The power source PS applies a sense current, a reset current, etc. to the photodetector element 10. If there is no need to flow a current from outside to the photodetector element 10, the input terminal Pin and the power source PS may be omitted. The output terminal Pout outputs, for example, a voltage between the first electrode 15 and the second electrode 16 that sandwich the photodetector element 10 in the stacking direction. The resistance value of the photodetector element 10 in the stacking direction can be found from Ohm's law by flowing a sense current in the stacking direction of the photodetector element 10. The output terminal P out is connected to the signal processing unit 11. G is connected to a reference potential and determines the reference potential of the receiving device 100. The reference potential in FIG. 3 is the ground G. The ground G may be provided outside the receiving device 100. The reference potential may be something other than the ground G.

[0037] The receiving device 100 and the transmitting device 200 are connected to, for example, a common reference potential (ground G). The receiving device 100 and the transmitting device 200 may have different reference potentials. If the receiving device 100 and the transmitting device 200 have the same reference potential, it is possible to reduce the generation of noise.

[0038] 4 is a cross-sectional view of the receiving device 100 according to the first embodiment. The receiving device 100 includes, for example, a photodetector element 10, an integrated circuit 20, and an interlayer insulating film 30. The photodetector element 10, the integrated circuit 20, and the interlayer insulating film 30 are formed on, for example, the same substrate Sb.

[0039] The integrated circuit 20 includes a signal processor 11 that processes a signal output from the photodetector element 10. For example, the integrated circuit 20 processes an output voltage from the photodetector element 10 (resistance value of the photodetector element 10 in the z direction) as a first signal (for example, "1") when the output voltage is equal to or greater than a threshold, and as a second signal (for example, "0") when the output voltage is less than the threshold. When the transmitting device 200 is formed on the same substrate Sb, the integrated circuit 20 may include a light source 201, an electric signal generating element 202, and an optical modulation element 203. The integrated circuit 20 and the photodetector element 10 are connected via, for example, a through-wire w that penetrates the interlayer insulating film 30. Instead of the through-wire w, wire bonding may be used to connect them.

[0040] The interlayer insulating film 30 is an insulator that insulates between wirings of a multilayer wiring or between elements. The interlayer insulating film 30 is, for example, an oxide, a nitride, or an oxynitride of Si, Al, or Mg. The interlayer insulating film 30 is, for example, a 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.

[0041] Fig. 5 is a cross-sectional view of the photodetector 10 according to the first embodiment. In Fig. 5, the first electrode 15 and the second electrode 16 are shown together, and the direction of magnetization of the ferromagnetic material in the initial state is indicated by an arrow.

[0042] The photodetector element 10 is a magnetic element having at least 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 photodetector element 10 may further include a third ferromagnetic layer 4, a magnetic coupling layer 5, an underlayer 6, a perpendicular magnetization induction layer 7, a cap layer 8, and a sidewall insulating layer 9.

[0043] The light detection element 10 is, for example, a magnetic tunnel junction (MTJ) element in which the spacer layer 3 is made of an insulating material. In this case, the light detection element 10 is an element in which the resistance value in the z direction (the resistance value when a current flows in the z direction) changes according to the change in the relative angle between the magnetization direction of the first ferromagnetic layer 1 and the magnetization direction of the second ferromagnetic layer 2. Such an element is also called a magnetoresistance effect element.

[0044] The first ferromagnetic layer 1 is a light detection layer whose magnetization direction changes when light is irradiated from the outside. The first ferromagnetic layer 1 is also called a magnetization free layer. The magnetization free layer is a layer including a magnetic material whose magnetization direction 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 light detection element 10, or an external magnetic field. Since the magnetization of a ferromagnetic material can change direction following a high-speed change in the intensity of light irradiated to the ferromagnetic material (high-frequency optical signal), by using the first ferromagnetic layer 1 as a light detection layer, the receiving device 100 can receive a high-frequency optical signal, enabling high-speed optical communication.

[0045] The first ferromagnetic layer 1 includes a ferromagnetic material. The first ferromagnetic layer 1 includes at least one of Co, Fe, and Ni, for example. The first ferromagnetic layer 1 includes a magnetic element such as Co, Fe, or Ni, for example. The first ferromagnetic layer 1 may include a nonmagnetic element such as B, Mg, Hf, or Gd, in addition to the magnetic element as described above. The first ferromagnetic layer 1 may be, for example, an alloy including a magnetic element and a nonmagnetic element. The first ferromagnetic layer 1 may be composed of a plurality of layers. The first ferromagnetic layer 1 is, 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.

[0046] 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).

[0047] 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 application effect from the layers above and below the first ferromagnetic layer 1 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer is enhanced. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high, the force that causes the magnetization 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 application effect from the layers above and below the first ferromagnetic layer 1 is relatively weak, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is weakened.

[0048] When the thickness of the first ferromagnetic layer 1 is decreased, the volume of the ferromagnetic body is decreased, and when the thickness is increased, the volume of the ferromagnetic body is increased. The responsiveness of the magnetization of the first ferromagnetic layer 1 when external energy is applied is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and the volume (V) of the first ferromagnetic layer 1. In other words, when the product of the magnetic anisotropy and the volume of the first ferromagnetic layer 1 is decreased, the responsiveness to the optical signal L1 at ultra-high speed is increased. From this viewpoint, as the optical communication becomes ultra-high speed, 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. In other words, it is preferable to reduce the thickness of the first ferromagnetic layer 1 as the communication speed becomes ultra-high.

[0049] When 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 in the first ferromagnetic layer 1. That is, the first ferromagnetic layer 1 may be a laminate in which a ferromagnetic layer, an insertion layer, and a ferromagnetic layer are laminated 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 0.6 nm.

[0050] 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 magnetization direction is less likely to change than that of 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 magnetization axis in the same direction as the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be an in-plane magnetization film or a perpendicular magnetization film.

[0051] 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 laminate in which Co is 0.4 nm to 1.0 nm thick, Mo is 0.1 nm to 0.5 nm thick, a CoFeB alloy is 0.3 nm to 1.0 nm thick, and Fe is 0.3 nm to 1.0 nm thick, laminated in this order.

[0052] The magnetization of the second ferromagnetic layer 2 may be fixed, for example, by magnetic coupling with the third ferromagnetic layer 4 via the magnetic coupling layer 5. In this case, the combination of the second ferromagnetic layer 2, the magnetic coupling layer 5, and the third ferromagnetic layer 4 may be referred to as a magnetization fixed layer.

[0053] The third ferromagnetic layer 4 is magnetically coupled to the second ferromagnetic layer 2, for example. The magnetic coupling is, for example, an antiferromagnetic coupling, which occurs due to RKKY interaction. The material constituting the third ferromagnetic layer 4 is, for example, the same as that of the first ferromagnetic layer 1. The third ferromagnetic layer 4 is, for example, a laminated film in which Co and Pt are alternately laminated, or a laminated film in which Co and Ni are alternately laminated. The magnetic coupling layer 5 is, for example, Ru, Ir, or the like. The film thickness of the magnetic coupling layer 5 is, for example, a film thickness at which the second ferromagnetic layer 2 and the third ferromagnetic layer 4 are antiferromagnetically coupled due to the RKKY interaction.

[0054] The spacer layer 3 is a non-magnetic layer disposed between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The spacer layer 3 is composed of a layer made of a conductor, an insulator, or a semiconductor, or a layer containing a current-carrying point made of a conductor in an insulator. The thickness of the spacer layer 3 can be adjusted according to the orientation directions of the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 in the initial state described later.

[0055] For example, when the spacer layer 3 is made of an insulator, the photodetector element 10 has a magnetic tunnel junction (MTJ) consisting of the first ferromagnetic layer 1, the spacer layer 3, and the second ferromagnetic layer 2. Such an element is called an MTJ element. In this case, the photodetector element 10 can exhibit a tunnel magnetoresistance (TMR) effect. For example, when the spacer layer 3 is made of a metal, the photodetector element 10 can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element. The photodetector element 10 may be called an MTJ element, a GMR element, or the like, depending on the material of the spacer layer 3, but is also collectively called a magnetoresistance effect element.

[0056] 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. These insulating materials may also contain elements such as Al, B, Si, Mg, or magnetic elements such as Co, Fe, Ni. A high magnetoresistance ratio can be obtained by adjusting the thickness of the spacer layer 3 so that a high TMR effect is generated between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. In order to efficiently utilize the TMR effect, the thickness of the spacer layer 3 may be about 0.5 to 5.0 nm, or about 1.0 to 2.5 nm.

[0057] When the spacer layer 3 is made of a nonmagnetic conductive material, a conductive material such as Cu, Ag, Au, Ru, etc. can be used. In order 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.

[0058] When the spacer layer 3 is made of a nonmagnetic semiconductor material, it can be made of a material such as 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.

[0059] When a layer including current-carrying points formed by a conductor in a nonmagnetic insulator is used as the spacer layer 3, the nonmagnetic insulator made of aluminum oxide or magnesium oxide may have a structure including current-carrying points formed by a nonmagnetic conductor such as Cu, Au, or Al. 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 about 1.0 to 2.5 nm. The current-carrying points are, for example, columnar bodies with a diameter of 1 nm or more and 5 nm or less when viewed from a direction perpendicular to the film surface.

[0060] The underlayer 6 shown in FIG. 5 is, for example, on the second electrode 16. The underlayer 6 is a seed layer or a buffer layer. The seed layer enhances the crystallinity of the layer laminated on the seed layer. The seed layer is, for example, Pt, Ru, Hf, Zr, or NiFeCr. The seed layer has a thickness of, for example, 1 nm or more and 5 nm or less. The buffer layer is a layer that relieves lattice mismatch between different crystals. The buffer layer is, for example, Ta, Ti, W, Zr, Hf, or a nitride of these elements. The buffer layer has a thickness of, for example, 1 nm or more and 5 nm or less.

[0061] The perpendicular magnetization induced layer 7 is formed when the first ferromagnetic layer 1 is a perpendicular magnetization film. The perpendicular magnetization induced layer 7 is laminated on the first ferromagnetic layer 1. The perpendicular magnetization induced layer 7 induces perpendicular magnetic anisotropy in the first ferromagnetic layer 1. The perpendicular magnetization induced layer 7 is made of, for example, magnesium oxide, W, Ta, Mo, or the like. When the perpendicular magnetization induced layer 7 is made of magnesium oxide, it is preferable that the magnesium oxide has oxygen deficiency in order to increase the conductivity. The film thickness of the perpendicular magnetization induced layer 7 is, for example, 0.5 nm or more and 2.0 nm or less.

[0062] The cap layer 8 is between the first ferromagnetic layer 1 and the first electrode 15. The cap layer 8 prevents damage to the lower layer during the process and improves the crystallinity of the lower layer during annealing. The thickness of the cap layer 8 is, for example, 3 nm or less so that the first ferromagnetic layer 1 is irradiated with sufficient light.

[0063] The sidewall insulating layer 9 covers the periphery of the stack including the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The sidewall insulating layer 9 is made of the same material as the interlayer insulating film 30, for example.

[0064] The first electrode 15 is transparent to light in the wavelength region used for the optical signal L1, for example. The wavelength region used for the optical signal L1 is, for example, 300 nm or more and 2 μm or less, including the visible light region and the near infrared light region. The first electrode 15 is a transparent electrode including a transparent electrode material of an oxide, such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). The first electrode 15 may be configured to have a plurality of columnar metals in these transparent electrode materials. In this case, the film thickness of the first electrode 15 is, for example, 10 nm to 300 nm. It is not essential to use the above-mentioned transparent electrode material for the first electrode 15, and a metal material such as Au, Cu, or Al may be used with a thin film thickness to allow light from the outside to reach the first ferromagnetic layer 1. When a metal is used as the material for the first electrode 15, the film thickness of the first electrode 15 is, for example, 3 to 10 nm. In particular, Au has a higher transmittance for light with wavelengths near blue than other metal materials. The first electrode 15 may have an anti-reflection film on the irradiation surface onto which light is irradiated.

[0065] The second electrode 16 is made of a material having electrical conductivity. The second electrode 16 is made of, for example, a metal such as Cu, Al, or Au. Ta or Ti may be laminated above and below these metals. A laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN may be used. TiN or TaN may be used as the second electrode 16. The film thickness of the second electrode 16 is, for example, 200 nm to 800 nm. The second electrode 16 may be transparent to light in the wavelength range used by the optical signal L1. As with the first electrode 15, the material of the second electrode 16 may be, for example, a transparent electrode material of an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). Even when light is irradiated from the first electrode 15, the light may reach the second electrode 16 depending on the intensity of the light. In this case, since the second electrode 16 is composed of an oxide transparent electrode material, the reflection of light at the interface between the second electrode 16 and the layer in contact with it can be suppressed compared to when the second electrode 16 is composed of a metal.

[0066] The light detection element 10 is fabricated through a process of stacking each layer, an annealing process, and a processing process. First, the underlayer 6, the third ferromagnetic layer 4, the magnetic coupling layer 5, the second ferromagnetic layer 2, the spacer layer 3, the first ferromagnetic layer 1, the perpendicular magnetization induction layer 7, and the cap layer 8 are stacked in this order on the second electrode 16. Each layer is formed by, for example, sputtering.

[0067] Next, the laminated film is annealed. The annealing temperature is, for example, 250° C. to 450° C. When the laminated film is formed on the same substrate as the semiconductor circuit, it is preferable to anneal the laminated film at 400° C. or higher. Thereafter, the laminated film is processed into a predetermined columnar body by photolithography and etching. The columnar body may be a cylindrical body or a rectangular column. For example, the minimum width of the columnar body as viewed from the z direction may be 10 nm or more and 2000 nm or less, or 30 nm or more and 500 nm or less.

[0068] Next, an insulating layer is formed so as to cover the side surfaces of the pillars. The insulating layer becomes the sidewall insulating layer 9. The sidewall insulating layer 9 may be laminated multiple times. Next, the upper surface of the cap layer 8 is exposed from the sidewall insulating layer 9 by chemical mechanical polishing (CMP), and a first electrode 15 is formed on the cap layer 8. Through the above steps, the photodetector element 10 is obtained.

[0069] Next, the operation of the photodetector 10 according to the first embodiment will be described. The first ferromagnetic layer 1 is irradiated with light including an optical signal L1 having a change in optical intensity. A lens may be disposed on the first ferromagnetic layer 1 side in the stacking direction of the photodetector 10, so that the first ferromagnetic layer 1 is irradiated with concentrated light through the lens. The lens may be formed in a wafer process for forming the photodetector 10. The resistance value in the z direction of the photodetector 10 changes when the first ferromagnetic layer 1 is irradiated with light including the optical signal L1. An example will be described in which the intensity of the light irradiated to the first ferromagnetic layer 1 has two levels, a first intensity and a second intensity. The second intensity is assumed to be greater than the first intensity. The first intensity may be the case where the intensity of the light irradiated to the first ferromagnetic layer 1 is zero.

[0070] The operation of the light detection element 10 according to the first embodiment has two patterns. The first pattern is a case where the output voltage from the light detection element 10 is higher at the second intensity than at the first intensity. The second pattern is a case where the output voltage from the light detection element 10 is higher at the first intensity than at the second intensity.

[0071] 6 and 7 are diagrams for explaining the operation of the first pattern of the photodetector 10 according to the first embodiment. Two mechanisms are considered as the mechanism of operation of the photodetector 10, and FIG. 6 is a diagram for explaining the first mechanism, and FIG. 7 is a diagram for explaining the second mechanism. In the upper graphs of FIG. 6 and FIG. 7, the vertical axis represents the intensity of light irradiated to the first ferromagnetic layer 1, and the horizontal axis represents time. In the lower graphs of FIG. 6 and FIG. 7, the vertical axis represents the resistance value in the z direction of the photodetector 10, and the horizontal axis represents time.

[0072] First, in a state where the first ferromagnetic layer 1 is irradiated with light of a first intensity (hereinafter referred to as an initial state), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are parallel to each other, the resistance value of the photodetector 10 in the z direction indicates a first resistance value R1, and the magnitude of the output voltage from the photodetector 10 indicates a first value. The resistance value of the photodetector 10 in the z direction is calculated from the voltage value generated at both ends of the photodetector 10 in the z direction by passing a sense current Is through the photodetector 10 in the z direction, using Ohm's law. The output voltage from the photodetector 10 is generated between the first electrode 15 and the second electrode 16. In the case of the first pattern shown in FIG. 6, it is preferable to pass the sense current Is from the first ferromagnetic layer 1 to the second ferromagnetic layer 2. By passing the sense current Is in this direction, a spin transfer torque in the same direction as the magnetization M2 of the second ferromagnetic layer 2 acts on the magnetization M1 of the first ferromagnetic layer 1, and the magnetizations M1 and M2 become parallel in the initial state. In addition, by passing the sense current Is in this direction, it is possible to prevent the magnetization M1 of the first ferromagnetic layer 1 from reversing during operation.

[0073] Next, the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity. The second intensity is greater than the first intensity, and the magnetization M1 of the first ferromagnetic layer 1 changes from the initial state due to the external energy caused by the light irradiation. The state of the magnetization M1 is, for example, the tilt angle or magnitude with respect to the z direction. For example, as shown in FIG. 6, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnetization M1 tilts with respect to the z direction. The angle between the direction of the magnetization M1 of the first ferromagnetic layer 1 in a state in which the first ferromagnetic layer 1 is not irradiated with light including the optical signal L1 and the magnetization direction of the first ferromagnetic layer 1 at the second intensity is greater than 0° and smaller than 90°. For example, as shown in FIG. 7, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnitude of the magnetization M1 decreases. When the magnetization M1 of the first ferromagnetic layer 1 changes from the initial state, the resistance value in the z direction of the photodetector element 10 exhibits a second resistance value R2, and the magnitude of the output voltage from the photodetector element 10 exhibits a second value.

[0074] That is, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the resistance value in the z direction of the photodetector element 10 changes from the first resistance value R1 to the second resistance value R2. In other words, the resistance value in the z direction of the photodetector element 10 changes from the first resistance value R1 to the second resistance value R2 in response to the change in the intensity of the light irradiated to the first ferromagnetic layer from the first intensity to the second intensity. The second resistance value R2 is greater than the first resistance value R1, and the second value of the output voltage is greater than the first value. The second resistance value R2 is between the resistance value (first resistance value R1) when the magnetization M1 and the magnetization M2 are parallel and the resistance value when the magnetization M1 and the magnetization M2 are antiparallel. It is preferable that the magnetization M1 of the first ferromagnetic layer 1 is not reversed by irradiation of the first ferromagnetic layer 1 with light including the optical signal L1.

[0075] 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. Therefore, in the case shown in FIG. 6, the magnetization M1 tries to return to a parallel state with the magnetization M2, and when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the photodetector 10 returns to its initial state. In the case shown in FIG. 7, when the intensity of the light irradiated to the first ferromagnetic layer 1 returns to the first intensity, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 returns to its original value, and the photodetector 10 returns to its initial state. In either case, when the magnetization M1 returns to its initial state, the resistance value in the z direction of the photodetector 10 returns to the first resistance value R1. In other words, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the resistance value in the z direction of the photodetector 10 changes from the second resistance value R2 to the first resistance value R1. In other words, the resistance value in the z-direction of the photodetector element 10 changes from the second resistance value R2 to the first resistance value R1 in response to a change from the second intensity to the first intensity of the light irradiated to the first ferromagnetic layer.

[0076] In either mechanism, when the photodetector 10 according to the first embodiment operates in the first pattern, the resistance value in the stacking direction of the photodetector 10 changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer 1. That is, the output voltage from the photodetector 10 changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer 1. As a result, the photodetector 10 can convert the change in the intensity of the optical signal L1 into a change in the resistance value in the z direction of the photodetector 10, that is, a change in the output voltage from the photodetector 10. In the example shown in FIG. 6 and FIG. 7, the resistance value in the stacking direction of the photodetector 10, that is, the output voltage from the photodetector 10, corresponds to the intensity of the light irradiated to the first ferromagnetic layer 1. The output voltage signal from the photodetector 10, which indicates the resistance value in the z direction of the photodetector 10, is sent to the signal processor 11, and is processed as a first signal (e.g., “1”) when the output voltage from the photodetector 10 (the resistance value in the z direction of the photodetector 10) is equal to or greater than a threshold value, and as a second signal (e.g., “0”) when the output voltage is less than the threshold value. That is, the receiving device 100 receives the optical signal L1 based on the output voltage from the light detecting element 10 (the resistance value of the light detecting element 10 in the z direction).

[0077] 8 and 9 are diagrams for explaining the operation of the second pattern of the photodetector 10 according to the first embodiment. FIG. 8 is a diagram for explaining the first mechanism, and FIG. 9 is a diagram for explaining the second mechanism. In the upper graphs of FIG. 8 and FIG. 9, the vertical axis represents the intensity of light irradiated to the first ferromagnetic layer 1, and the horizontal axis represents time. In the lower graphs of FIG. 8 and FIG. 9, the vertical axis represents the resistance value in the z direction of the photodetector 10, and the horizontal axis represents time.

[0078] The second pattern differs from the first pattern in that in the initial state, the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are antiparallel, and the operating principle is the same as that of the first pattern.

[0079] First, in a state where the first ferromagnetic layer 1 is irradiated with light of a first intensity, the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are in an anti-parallel state, the resistance value in the z direction of the photodetector 10 indicates a first resistance value R1', and the magnitude of the output voltage from the photodetector 10 indicates a first value. In the case of the second pattern shown in FIG. 8 and FIG. 9, it is preferable to flow the sense current Is from the second ferromagnetic layer 2 to the first ferromagnetic layer 1. By flowing the sense current Is in this direction, a spin transfer torque in the opposite direction to the magnetization M2 of the second ferromagnetic layer 2 acts on the magnetization M1 of the first ferromagnetic layer 1, and the magnetization M1 and the magnetization M2 become anti-parallel in the initial state. In the second pattern, the direction of the sense current Is is reversed from that of the first pattern, so that the magnetization direction (stable magnetization direction) of the first ferromagnetic layer 1 in the initial state is reversed.

[0080] Next, the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity. The second intensity is greater than the first intensity, and the magnetization M1 of the first ferromagnetic layer 1 changes from the initial state. For example, as shown in FIG. 8, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnetization M1 tilts with respect to the z direction. Also, for example, as shown in FIG. 9, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnitude of the magnetization M1 decreases. When the magnetization M1 of the first ferromagnetic layer 1 changes, the resistance value in the z direction of the photodetector element 10 indicates a second resistance value R2', and the magnitude of the output voltage from the photodetector element 10 indicates a first value. That is, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the resistance value in the z direction of the photodetector element 10 changes from the first resistance value R1' to the second resistance value R2'. In other words, the resistance value in the z direction of the photodetector element 10 changes from a first resistance value R1' to a second resistance value R2' in response to a change from a first intensity to a second intensity of the light irradiated to the first ferromagnetic layer. The second resistance value R2' is smaller than the first resistance value R1', and the second value of the output voltage is smaller than the first value. The second resistance value R2' is between the resistance value (first resistance value R1') when the magnetization M1 and the magnetization M2 are antiparallel and the resistance value (first resistance value R1 in FIG. 6) when the magnetization M1 and the magnetization M2 are parallel.

[0081] A spin transfer torque in the opposite direction to the magnetization M2 of the second ferromagnetic layer 2 acts on the magnetization M1 of the first ferromagnetic layer 1. Therefore, in the case shown in FIG. 8, the magnetization M1 tilted from the initial state returns to the initial state when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the second intensity to the first intensity. In the case shown in FIG. 9, when the intensity of the light irradiated to the first ferromagnetic layer 1 returns to the first intensity, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 returns to the original value, and the photodetector element 10 returns to the initial state. When the magnetization M1 returns to the initial state, the resistance value in the z direction of the photodetector element 10 returns to the first resistance value R1'. In other words, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the resistance value in the z direction of the photodetector element 10 changes from the second resistance value R2' to the first resistance value R1'. In other words, the resistance value in the z-direction of the photodetector element 10 changes from the second resistance value R2' to the first resistance value R1' in response to a change from the second intensity to the first intensity of light irradiating the first ferromagnetic layer.

[0082] In either mechanism, when the photodetector 10 according to the first embodiment operates in the second pattern, the resistance value in the stacking direction of the photodetector 10 changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer 1. That is, the output voltage from the photodetector 10 changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer 1. As a result, the photodetector 10 can convert the change in the intensity of the optical signal L1 into a change in the resistance value in the z direction of the photodetector 10, that is, a change in the output voltage from the photodetector 10. In the example shown in FIG. 8 and FIG. 9, the resistance value in the stacking direction of the photodetector 10, that is, the output voltage from the photodetector 10, corresponds to the intensity of the light irradiated to the first ferromagnetic layer 1. The output voltage signal from the photodetector 10, which indicates the resistance value in the z direction of the photodetector 10, is sent to the signal processor 11, and is processed as a first signal (e.g., “1”) when the output voltage from the photodetector 10 (the resistance value in the z direction of the photodetector 10) is equal to or greater than a threshold value, and as a second signal (e.g., “0”) when the output voltage is less than the threshold value. That is, the receiving device 100 receives the optical signal L1 based on the output voltage from the light detecting element 10 (the resistance value of the light detecting element 10 in the z direction).

[0083] In this way, by applying a bias to the magnetization M1 of the first ferromagnetic layer 1, which acts to orient the magnetization M1 in a direction parallel or anti-parallel to the direction of the magnetization M2, the resistance value of the photodetector 10, i.e., the output voltage from the photodetector 10, can be changed in response to a change in the intensity of the light irradiated to the first ferromagnetic layer 1. In the examples of the first and second patterns described above, the application effect of the spin transfer torque by the sense current Is is used as the bias application effect. The bias application effect is not limited to the application effect of the spin transfer torque by the sense current Is, and for example, another bias application effect as shown in the second to fourth modified examples described later may be used.

[0084] Here, the orientation directions of the magnetization M1 and the magnetization M2 in the initial state may not be oriented in the correct direction due to external factors such as an external magnetic field, heat, etc. For this reason, a reset current may be applied in the z direction of the photodetector element 10 before operating the photodetector element 10 according to the first embodiment.

[0085] The reset current has a current density sufficient to sufficiently reverse the magnetization M1 of the first ferromagnetic layer 1. In the first pattern, the reset current is passed from the first ferromagnetic layer 1 to the second ferromagnetic layer 2. In the second pattern, the reset current is passed from the second ferromagnetic layer 2 to the first ferromagnetic layer 1. When the reset current is passed in the z direction of the photodetector element 10, a spin transfer torque (STT) is applied to the magnetization M1, and the magnetization M1 of the first ferromagnetic layer 1 is aligned in the correct direction. In each pattern, the value of the reset current is greater than the value of the sense current.

[0086] Up to this point, we have explained an example in which the light irradiated to the first ferromagnetic layer 1 has two levels of intensity, a first intensity and a second intensity. However, the photodetector 10 of the first embodiment can also read multi-value information from the optical signal L1 by increasing the intensity of the light irradiated to the first ferromagnetic layer 1 to more than two levels.

[0087] 10 and 11 show the behavior of the photodetector 10 according to the first embodiment when multiple values ​​are output. FIG. 10 is a diagram for explaining the first mechanism, and FIG. 11 is a diagram for explaining the second mechanism. FIG. 10 and FIG. 11 show the magnetization state and the resistance value in the z direction of the photodetector 10 at the first intensity, the second intensity, the third intensity, and the fourth intensity, respectively, from the left. The intensities of the light irradiated to the first ferromagnetic layer 1 are stronger in the order of the fourth intensity, the third intensity, the second intensity, and the first intensity. At the first intensity, the intensity of the irradiated light may be zero.

[0088] As shown in FIG. 10, when the magnetization M1 is tilted according to the intensity of the irradiated light, the angle change of the magnetization M1 from the initial state becomes larger as the intensity of the light irradiated to the first ferromagnetic layer 1 becomes larger. The angles between the direction of the magnetization M1 of the first ferromagnetic layer 1 in a state where the first ferromagnetic layer 1 is not irradiated with light including the optical signal L1 and the direction of the magnetization M1 at the second intensity, the third intensity, and the fourth intensity are all greater than 0° and smaller than 90°. The change in the resistance value in the z direction of the photodetector 10 from the initial state becomes larger as the angle change of the magnetization M1 from the initial state becomes larger. In the example shown in FIG. 10, the resistance value in the z direction of the photodetector 10 becomes larger as the angle change of the magnetization M1 from the initial state becomes larger. Therefore, the resistance value in the z direction of the photodetector 10 is different for each of the first intensity, the second intensity, the third intensity, and the fourth intensity. The photodetector 10 according to the first embodiment can read out information of four values, for example, "0", "1", "2", and "3", by defining the output voltage threshold (resistance threshold) in multiple stages. Although the case where four values ​​are read out is shown as an example here, the number of values ​​to be read out can be freely designed by setting the output voltage threshold (resistance threshold). It is preferable that the magnetization M1 of the first ferromagnetic layer 1 is not reversed by irradiation of the first ferromagnetic layer 1 with light including the optical signal L1.

[0089] 11, when the intensity of the light irradiated to the first ferromagnetic layer 1 increases, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 decreases from the initial state due to the external energy caused by the light irradiation. When the magnetization M1 of the first ferromagnetic layer 1 decreases from the initial state, the resistance value in the z direction of the photodetector element 10 changes. For example, the resistance value in the z direction of the photodetector element 10 changes to a second resistance value R2, a third resistance value R3, and a fourth resistance value R4 according to the magnitude of the magnetization M1 of the first ferromagnetic layer 1. Therefore, similar to the case of FIG. 10, the difference in the output voltage from the photodetector element 10 can be output as multi-value or analog data.

[0090] In addition, although the magnetization M1 and magnetization M2 are parallel in the initial state, the magnetization M1 and magnetization M2 may be antiparallel in the initial state. As in Fig. 10, when the magnetization M1 tilts according to the intensity of the irradiated light, the resistance value in the z direction of the light detection element 10 decreases as the angle change of the magnetization M1 from the initial state increases.

[0091] Next, the operation when an abnormality occurs in the photodetector 10 will be described. Fig. 12 shows the behavior of the photodetector 10 according to the first embodiment when an abnormality occurs in the photodetector 10. In the upper graph of Fig. 12, the vertical axis represents the intensity of light irradiated to the first ferromagnetic layer 1, and the horizontal axis represents time. In the lower graph of Fig. 12, the vertical axis represents the resistance value in the z direction of the photodetector 10, and the horizontal axis represents time.

[0092] 12 shows an example of an abnormality that occurs when the light detection element 10 is operating in the first pattern. As an example of an abnormality, a case is shown where the intensity of a part of the optical signal L1 irradiated to the first ferromagnetic layer 1 becomes abnormally strong. The abnormality is not limited to an excessive optical intensity, but may be, for example, a change in the operating temperature or a change in the intensity of the applied external magnetic field. When the operating temperature or the external magnetic field changes, the stability of the magnetization M1 also changes.

[0093] When the photodetector element 10 operates normally in the first pattern, the resistance value in the z direction of the photodetector element 10 changes between the first resistance value R1 and the second resistance value R2. On the other hand, when the first ferromagnetic layer 1 is irradiated with excessive light, the magnetization M1 may be significantly tilted from the initial state and the magnetization M1 may be reversed. In this case, the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 become antiparallel, and the resistance value becomes the third resistance value R3 (same as the first resistance value R1' of the second pattern). The third resistance value R3 is larger than the first resistance value R1 and the second resistance value R2, and an abnormality is detected.

[0094] If an abnormality occurs in the photodetector element 10, the above-mentioned reset current is applied. By applying the reset current, the magnetization M1 of the first ferromagnetic layer 1 returns to the correct direction, and the photodetector element 10 can be used normally again. Here, the first mechanism is explained, but the same principle also applies to the second mechanism. In the case of the second mechanism, when the first ferromagnetic layer 1 is irradiated with excessive light, the magnetization M1 is significantly reduced from the initial state, and the magnetization M1 may be reversed.

[0095] As described above, the transmitting / receiving device 300 and the receiving device 100 according to the first embodiment receive an optical signal based on the output voltage from the optical detection element 10 (the resistance value of the optical detection element 10). Furthermore, the optical detection element 10 according to the first embodiment can convert a change in the intensity of the optical signal L1 into a change in the output voltage from the optical detection element 10 (a change in the resistance value of the optical detection element 10 in the z direction), and can support high-speed communication.

[0096] As described above, the smaller the volume of the first ferromagnetic layer 1, the easier it is to tilt the magnetization M1 of the first ferromagnetic layer 1. In other words, by reducing the volume of the first ferromagnetic layer 1, the magnetization M1 can be tilted even with a small amount of light. That is, the photodetector 10 according to the first embodiment can receive the optical signal L1 with high sensitivity.

[0097] More precisely, the tendency of the magnetization M1 to tilt is determined by the magnitude of the product (KuV) of the magnetic anisotropy (Ku) and the volume (V) of the first ferromagnetic layer 1. The smaller the KuV, the smaller the amount of light required to tilt the magnetization, and the larger the KuV, the larger the amount of light required to tilt the magnetization. In other words, the KuV of the first ferromagnetic layer 1 is designed according to the amount of light irradiated from the outside used in the application. In the case of extremely minute amounts of light, such as photon detection, the KuV of the first ferromagnetic layer can be reduced to detect these minute amounts of light. This is a great advantage, as conventional light detection elements cannot detect such minute amounts of light. In other words, in order to reduce the KuV, the volume of the first ferromagnetic layer 1 can be reduced, that is, the element area can be reduced, or the film thickness of the first ferromagnetic layer 1 can be reduced, thereby making it possible to detect photons.

[0098] Furthermore, the photodetector 10 according to the first embodiment can receive the optical signal L1 regardless of the wavelength range of the irradiated light. For semiconductor photodetectors using a pn junction, the appropriate semiconductor material varies depending on the wavelength of the irradiated light. For example, InGaAs or the like is used to detect near-infrared light with a wavelength of 1.3 μm or more and 1.5 μm or less. For example, silicon is used to detect visible light with a wavelength of 400 nm or more and 800 nm or less.

[0099] Fig. 13 is a diagram showing a simulation result of the sensitivity of the photodetector 10 (Example) according to the first embodiment when the wavelength of the irradiated light is 1.5 μm (near-infrared light), and a curve (an approximation curve of the sensitivity data of several known examples) showing the characteristic level of a conventional semiconductor photodiode using InGaAs (Comparative Example 1). Fig. 14 is a diagram showing a simulation result of the sensitivity of the photodetector 10 (Example) according to the first embodiment when the wavelength of the irradiated light is 520 nm (visible light), and a curve (an approximation curve of the sensitivity data of several known examples) showing the characteristic level of a conventional semiconductor photodiode using silicon (Comparative Example 2).

[0100] The conditions for the simulation of the embodiment were set as follows: The photodetector element 10 has a square planar shape with a side length of 200 nm and an area resistance (RA) of 5 Ωμm. 2 The magnetoresistance change rate (MR change rate) was set to 65%. The second ferromagnetic layer 2 (magnetization fixed layer) was an alloy layer containing CoFeB with a thickness of 2 nm, the spacer layer 3 was made of MgO, and the first ferromagnetic layer 1 was an alloy layer containing CoFeB with a thickness of 1.2 nm. The spot diameter of the light irradiated to the light detection element 10 was set to 900 nmφ. The sensitivity on the vertical axis of the graph is the output current amount per unit light irradiation amount. In the embodiment, the output voltage, which is the potential difference between the first electrode 15 and the second electrode 16, was divided by the minimum resistance value of the light detection element 10 (in the case of the first mechanism, the resistance value when the magnetization M1 and the magnetization M2 are parallel) to convert the output current amount.

[0101] Considering practical constraints (optical signal strength, matching with peripheral circuits), a sensitivity of 0.5 A / W or more is often required. As shown in FIG. 13, even Comparative Example 1 using InGaAs suitable for near-infrared light cannot receive high-speed optical signals exceeding 40 GHz with good sensitivity. In contrast, the photodetector 10 according to the embodiment can receive high-speed signals exceeding 100 GHz with good sensitivity. Also, as shown in FIG. 14, Comparative Example 2 using silicon suitable for visible light can only receive optical signals below 3 GHz with good sensitivity, and cannot handle high-speed signals. In contrast, the photodetector 10 according to the embodiment can receive high-speed signals exceeding 100 GHz with good sensitivity, as in the case of near-infrared light.

[0102] That is, the photodetector 10 according to the first embodiment can receive high-speed optical signals with good sensitivity regardless of whether the signal is visible light or near-infrared light. Although examples of visible light and near-infrared light are shown here, the present invention is not limited to these examples, and the photodetector 10 can also respond quickly to, for example, ultraviolet light having a wavelength of 200 nm or more and less than 400 nm.

[0103] Although the first embodiment has been described in detail above with reference to the drawings, the first embodiment is not limited to this example.

[0104] (First Modification) Fig. 15 is a circuit diagram of a transmission / reception device 301 according to a first modified example. The transmission / reception device 301 according to the first modified example differs from the transmission / reception device 300 in that the reception device 101 has an analog-digital converter AD. The same components as those in Fig. 3 are denoted by the same reference numerals and will not be described.

[0105] The analog-to-digital converter AD is connected to the first electrode 15 and the output terminal P out and . The analog-to-digital converter AD converts the output voltage from the photodetection element 10 (the resistance value of the photodetection element 10 in the z direction) into digital data. In other words, the transceiver 301 according to the first modified example is less susceptible to the effects of noise and the like. The transceiver 301 according to the first modified example can be particularly suitably used when the photodetection element 10 outputs multiple values.

[0106] (Second Modification) Fig. 16 is a cross-sectional view of the photodetector according to the second modification and its periphery taken along a plane along the z direction. Fig. 17 is a cross-sectional view of the photodetector according to the second modification and its periphery taken along an xy plane passing through the first ferromagnetic layer 1. The receiving device according to the second modification further includes a hard bias layer 40 that applies a bias magnetic field to the first ferromagnetic layer 1. The same components as those in Fig. 5 are denoted by the same reference numerals and will not be described.

[0107] The hard bias layer 40 is located at a position overlapping the first ferromagnetic layer 1 when viewed from any direction perpendicular to the z direction. A sidewall insulating layer 9 is provided between the hard bias layer 40 and the first ferromagnetic layer 1. As shown in FIG. 17 , the hard bias layer 40, for example, surrounds the periphery of the first ferromagnetic layer 1. There may be a plurality of hard bias layers 40, for example, sandwiching the first ferromagnetic layer 1 in any direction in the xy plane.

[0108] The hard bias layer 40 is a hard magnetic material. The hard bias layer 40 is, for example, a CoPt alloy, a CoPtCr alloy, an FePt alloy, or a laminated film in which Co layers and Pt layers are alternately laminated. The film thickness of the hard bias layer 40 is, for example, 2 nm or more and 30 nm or less. The shortest width of the hard bias layer 40 in the xy plane is, for example, 10 nm or more and 500 nm or less.

[0109] The hard bias layer 40 has an easy axis of magnetization in the same direction as the first ferromagnetic layer 1. The magnetization direction of the magnetization M40 of the hard bias layer 40 is opposite to the magnetization direction of the magnetization M1 of the first ferromagnetic layer 1 in a state where no light is irradiated. The hard bias layer 40 may be an in-plane magnetization film or a perpendicular magnetization film.

[0110] The fringing magnetic field generated from the hard bias layer 40 acts on the magnetization M1 as a bias magnetic field applied to the first ferromagnetic layer 1, and in the case of the first pattern described above, the magnetization M1 and the magnetization M2 are parallel in the initial state, and in the case of the second pattern described above, the magnetization M1 and the magnetization M2 are antiparallel in the initial state. The fringing magnetic field generated from the hard bias layer 40 also prevents the magnetization M1 of the first ferromagnetic layer 1 from reversing during operation. In other words, the application of the fringing magnetic field generated from the hard bias layer 40 to the first ferromagnetic layer 1 produces a bias application effect on the magnetization M1 of the first ferromagnetic layer 1.

[0111] (Third Modification) 18 is a cross-sectional view of a photodetector according to a third modified example taken along a plane along the z-direction. The photodetector according to the third modified example further includes a wiring layer 50. The same components as those in FIG. 5 are denoted by the same reference numerals and will not be described.

[0112] The wiring layer 50 is located between the first electrode 15 and the first ferromagnetic layer 1. The wiring layer 50 extends in any direction within the xy plane.

[0113] When a current flows along the wiring layer 50, a spin current is generated by the spin Hall effect, and spins are injected into the first ferromagnetic layer 1. The spins injected into the first ferromagnetic layer 1 apply a spin-orbit torque (SOT) to the magnetization M1 of the first ferromagnetic layer 1.

[0114] The wiring layer 50 includes, for example, a non-magnetic heavy metal as a main element. The main element is the element that has the highest ratio among the elements that constitute the wiring layer 50. The wiring layer 50 includes, for example, a heavy metal having a specific gravity equal to or greater than yttrium (Y). The non-magnetic heavy metal has a large atomic number of 39 or more and has d electrons or f electrons in the outermost shell, so that strong spin-orbit interaction occurs. The wiring layer 50 includes, for example, any one selected from the group consisting of Pt, W, Ta, Au, Hf, and Mo. In particular, Pt, W, Ta, and the like are more preferable elements. W and Ta preferably use a β-phase crystal structure in order to increase the spin-orbit interaction effect. The thickness of the wiring layer 50 is preferably 1 to 10 nm, more preferably 1 to 5 nm.

[0115] By passing a current through the wiring layer 50, spins are injected from the wiring layer 50 into the first ferromagnetic layer 1, and a bias effect is generated on the magnetization M1 of the first ferromagnetic layer 1. By changing the direction of the current passed through the wiring layer 50, the direction of the spins injected from the wiring layer 50 into the first ferromagnetic layer 1 can be changed, and the direction of the magnetization M1 of the first ferromagnetic layer 1 in the initial state (the stable magnetization direction of the magnetization M1) can be changed. Depending on the direction of the spins injected from the wiring layer 50 into the first ferromagnetic layer 1, the magnetization M1 and the magnetization M2 can be controlled to be parallel in the initial state in the case of the first pattern described above, and the magnetization M1 and the magnetization M2 can be controlled to be antiparallel in the initial state in the case of the second pattern described above. In addition, the spins injected from the wiring layer 50 into the first ferromagnetic layer 1 prevent the magnetization M1 of the first ferromagnetic layer 1 from being reversed during operation. The direction of the spins injected from the wiring layer 50 into the first ferromagnetic layer 1 can be freely controlled by the direction of the current flowing along the wiring layer 50.

[0116] (Fourth Modification) Fig. 19 is a cross-sectional view of receiving device 102 according to the fourth modified example taken along a plane along the z direction. Fig. 20 is a plan view of receiving device 102 according to the fourth modified example seen from the z direction. Receiving device 102 according to the fourth modified example further includes a soft magnetic material 60. The same components as those in Fig. 4 are denoted by the same reference numerals and will not be described.

[0117] The soft magnetic body 60 is a magnetic shield. When viewed from the z direction, the soft magnetic body 60 covers at least a part of the outer periphery of the photodetector element 10 from the outside. When viewed from any direction in the xy plane, the soft magnetic body 60 overlaps with at least a part of the first ferromagnetic layer 1. When viewed from the z direction of the photodetector element, for example, the soft magnetic body 60 covers the entire outer periphery of the photodetector element 10. When viewed from any direction in the xy plane, the soft magnetic body 60 overlaps with the entire outer periphery of the first ferromagnetic layer 1 in the z direction.

[0118] The soft magnetic body 60 is, for example, a metal or alloy containing at least one of Fe, Ni, and Co. The soft magnetic body 60 is, for example, a NiFe alloy. The soft magnetic body 60 may be a magnetic body having insulating properties. The soft magnetic body 60 is, for example, a ceramic such as ferrite. The soft magnetic body 60 is, for example, a rare earth iron garnet (RIG). Yttrium iron garnet (YIG) is an example of a rare earth iron garnet (RIG).

[0119] The soft magnetic material 60 can prevent an external magnetic field from being applied to the first ferromagnetic layer 1, and can prevent the first ferromagnetic layer 1 from exhibiting unexpected behavior.

[0120] (Fifth Modification) Fig. 21 is a cross-sectional view of receiving device 103 according to the fifth modified example taken along a plane along the z direction. Fig. 22 is a plan view of receiving device 103 according to the fifth modified example seen from the z direction. Receiving device 103 according to the fifth modified example further includes soft magnetic material 61. The same components as those in Fig. 4 are denoted by the same reference numerals and will not be described.

[0121] The soft magnetic body 61 is a magnetic shield. The soft magnetic body 61 differs from the soft magnetic body 60 in that the soft magnetic body 61 is also above and below the light detecting element 10. The soft magnetic body 61 surrounds the light detecting element 10 except for the opening 62. The soft magnetic body 61 can be made of the same material as the soft magnetic body 60.

[0122] The soft magnetic body 61 has an opening 62 on the upper side, which is the side on which light is incident to the photodetector element 10. The opening 62 is formed on the first ferromagnetic layer 1 side of the soft magnetic bodies 61 located above and below the photodetector element 10. In the opening 62, there is a mesh-shaped magnetic net 63 connected to the soft magnetic body 61. The magnetic net 63 includes a magnetic body, for example, includes the same material as the soft magnetic body 61.

[0123] The wiring connected to the first electrode 15 and the second electrode 16 is connected to an external contact provided outside the soft magnetic body 61 with an insulating layer 64 sandwiched therebetween.

[0124] The magnetic shielding effect is further enhanced by providing the soft magnetic material 61 above and below the photodetector element 10. Furthermore, by providing an opening 62 in the soft magnetic material 61, light having an optical signal L1 can be efficiently irradiated to the first ferromagnetic layer 1. Furthermore, by providing a magnetic mesh 63 in the opening 62, intrusion of an external magnetic field from the opening 62 can be suppressed.

[0125] (Sixth Modification) Fig. 23 is a cross-sectional view of a receiving device 104 according to a sixth modified example. The same components as those in Fig. 4 are given the same reference numerals and the description thereof will be omitted.

[0126] In the receiving device 104 according to the sixth modification, the photodetector element 10 is formed on a substrate Sb. In the receiving device 104 according to the sixth modification, the integrated circuit 20 may be formed in a peripheral portion of the substrate Sb where the photodetector element 10 is not formed, or may be formed outside the substrate. The integrated circuit 20 is connected to the photodetector element 10 via wiring.

[0127] "Second embodiment" The receiving device according to the second embodiment differs from the receiving device 100 according to the first embodiment in the operation of the photodetecting element. The element configuration of the receiving device according to the second embodiment is similar to that of the receiving device according to the first embodiment.

[0128] 24 is a diagram for explaining the operation of the receiving device according to the second embodiment. The receiving device according to the second embodiment processes a change in the output voltage from the photodetecting element 10 (resistance value in the z direction of the photodetecting element 10) within a predetermined time as a first signal (e.g., "1"), and a lack of change in the output voltage from the photodetecting element 10 (resistance value in the z direction of the photodetecting element 10) within a predetermined time as a second signal (e.g., "0"). The predetermined time is determined by the modulation frequency of the optical signal.

[0129] Hereinafter, the operation of the receiving device according to the second embodiment will be specifically described based on the example shown in FIG. 24. First, the optical signal irradiated to the photodetector 10 is defined. The optical signal is defined as "1" when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from a first intensity to a second intensity, and as "0" when the intensity of the light irradiated to the first ferromagnetic layer 1 is maintained at the first intensity for a predetermined time. The intensity of the light that has changed from the first intensity to the second intensity returns to the first intensity after a certain time has passed.

[0130] The optical signal is irradiated onto the first ferromagnetic layer 1 of the photodetector 10. When the intensity of the light irradiated onto the first ferromagnetic layer 1 changes from a first intensity to a second intensity, the magnetization M1 of the first ferromagnetic layer 1 is reversed. Note that when the intensity of the light irradiated onto the first ferromagnetic layer 1 returns from the second intensity to the first intensity, the magnetization M1 of the first ferromagnetic layer 1 is not reversed. The resistance value in the z direction of the photodetector changes from a low resistance R L From high resistance R H Or high resistance R H From low resistance R LIn other words, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, regardless of whether the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are parallel or antiparallel, the resistance value of the photodetection element 10, i.e., the output voltage from the photodetection element 10 changes when information of "1" is input as an optical signal. By defining a change in the output voltage from the photodetection element 10 (resistance value of the photodetection element 10 in the z direction) within a predetermined time as "1," the receiving device according to the second embodiment can receive an optical signal of "1" as a signal of "1" based on the output voltage from the photodetection element 10 (resistance value of the photodetection element 10).

[0131] On the other hand, when the first ferromagnetic layer 1 of the photodetector 10 is not irradiated with light or the intensity of the irradiated light is low, the magnetization M1 of the first ferromagnetic layer 1 maintains its state. Therefore, when the intensity of the light irradiated to the first ferromagnetic layer 1 is maintained at the first intensity for a predetermined time, the resistance value in the z direction of the photodetector 10, i.e., the output voltage from the photodetector 10 does not change. In other words, when information of "0" is input as an optical signal, the output voltage from the photodetector 10 (resistance value of the photodetector) does not change. By defining the absence of change in the output voltage from the photodetector 10 (resistance value of the photodetector 10 in the z direction) within a predetermined time as "0", the receiving device according to the second embodiment can receive the optical signal of "0" as a signal of "0" based on the output voltage from the photodetector 10 (resistance value of the photodetector 10).

[0132] As described above, the receiving device according to the second embodiment can receive an optical signal as the presence or absence of a change in the output voltage from the photodetector 10 within a predetermined time (a change in the resistance value of the photodetector in the z direction). The photodetector according to the second embodiment detects a change in resistance between when the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are parallel and when they are antiparallel, and the amount of change in the output voltage is large.

[0133] In the second embodiment, the direction of the sense current passed through the photodetector may be from the first ferromagnetic layer 1 to the second ferromagnetic layer 2, or from the second ferromagnetic layer 2 to the first ferromagnetic layer 1. In the third embodiment, the value of the sense current is preferably small so that the spin transfer torque caused by the sense current does not become too large. In the second embodiment, it does not matter whether the initial state is a state in which the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are parallel or antiparallel, so there is no need to apply a reset current.

[0134] Although the second embodiment has been described above in detail with reference to the drawings, the second embodiment is not limited to this example. For example, the first, fourth, fifth, and sixth modifications shown in the first embodiment can be applied.

[0135] Further, up to this point, the first and second embodiments have been described as examples in which the transmitting / receiving device is applied to the communication system 1000 shown in FIG. 1, but the communication system is not limited to this case.

[0136] For example, Fig. 25 is a conceptual diagram of another example of a communication system. A communication system 1001 shown in Fig. 25 is communication between two mobile terminal devices 500. The mobile terminal devices 500 are, for example, a smartphone, a tablet, or the like.

[0137] Each of the mobile terminal devices 500 includes a receiving device 100 and a transmitting device 200. An optical signal transmitted from the transmitting device 200 of one mobile terminal device 500 is received by the receiving device 100 of the other mobile terminal device 500. Light used for transmission and reception between the mobile terminal devices 500 is, for example, visible light. As the photodetector element 10 of each receiving device 100, either the photodetector element according to the first embodiment or the photodetector element according to the second embodiment is applied.

[0138] Further, for example, Fig. 26 is a conceptual diagram of another example of a communication system. A communication system 1002 shown in Fig. 26 is for communication between a mobile terminal device 500 and an information processing device 600. The information processing device 600 is, for example, a personal computer.

[0139] The mobile terminal device 500 includes a transmitting device 200, and the information processing device 600 includes a receiving device 100. An optical signal transmitted from the transmitting device 200 of the mobile terminal device 500 is received by the receiving device 100 of the information processing device 600. Light used for transmission and reception between the mobile terminal device 500 and the information processing device 600 is, for example, visible light. As the photodetector element 10 of each receiving device 100, any of the photodetector elements according to the first to third embodiments is applied.

[0140] As described above, the present invention is not limited to the above-described embodiment and modified examples, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0141] 1...first ferromagnetic layer, 2...second ferromagnetic layer, 3...spacer layer, 4...third ferromagnetic layer, 5...magnetic coupling layer, 6...underlayer, 7...perpendicular magnetization induction layer, 8...cap layer, 9...sidewall insulating layer, 10...photodetector element, 11...signal processing unit, 15...first electrode, 16...second electrode, 20...integrated circuit, 30...interlayer insulating film, 40...hard bias layer, 50...wiring layer, 60, 61...soft magnetic material, 62...opening, 63...magnetic mesh, 64...insulating layer, 100, 101, 102, 103...receiving device, 200...transmitting device, 201...light source, 202...electrical signal generating element, 203...light modulation element, 300, 301...transmitting / receiving device, 500...portable terminal device, 600...information processing device, 1000, 1001, 1002...communication system, AD...analog-to-digital converter, FB...fiber, G...ground, Is...sense current, M1, M2, M40...magnetization, P G ...Reference potential terminal, P in …Input terminal, P out …Output terminal, PS…Power supply, w…Through-through wiring

Claims

1. a magnetic element including a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; receiving the optical signal based on an output voltage from the magnetic element; an output voltage from the magnetic element changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer; A receiving device, wherein the angle between the magnetization direction of the first ferromagnetic layer when the light is not irradiated to the first ferromagnetic layer and the magnetization direction of the first ferromagnetic layer when the light is irradiated to the first ferromagnetic layer is greater than 0° and smaller than 90°.

2. A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; receiving the optical signal based on an output voltage from the magnetic element; an output voltage from the magnetic element changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer; The optical signal has at least two levels of intensity; a magnitude of an output voltage from the magnetic element exhibits a first value when the intensity of the light irradiated to the first ferromagnetic layer is a first intensity, and exhibits a second value when the intensity of the light irradiated to the first ferromagnetic layer is a second intensity, the second intensity being greater than the first intensity, If the second value is greater than the first value, a current is caused to flow from the first ferromagnetic layer to the second ferromagnetic layer; When the second value is smaller than the first value, a current is caused to flow from the second ferromagnetic layer to the first ferromagnetic layer.

3. A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; receiving the optical signal based on an output voltage from the magnetic element; a hard bias layer for applying a bias magnetic field to the first ferromagnetic layer; the hard bias layer is located so as to overlap the first ferromagnetic layer when viewed from any direction perpendicular to the stacking direction of the magnetic element; A receiving device, wherein the magnetization direction of the hard bias layer is opposite to the magnetization direction of the first ferromagnetic layer in the absence of light irradiation.

4. the magnetic element further includes a first electrode connected to the first ferromagnetic layer and a second electrode connected to the second ferromagnetic layer; 4. The receiving device according to claim 1, wherein the first electrode is transparent to light in a wavelength range used by the optical signal.

5. A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; receiving the optical signal based on an output voltage from the magnetic element; Further comprising a soft magnetic material; A receiving device, wherein the soft magnetic material covers at least a portion of the outer periphery of the magnetic element from the outside when viewed in a plan view from a stacking direction of the magnetic element.

6. The soft magnetic material is also present above and below the magnetic element in the lamination direction, The receiving device according to claim 5 , wherein the soft magnetic material on the first ferromagnetic layer side out of the soft magnetic materials above and below the magnetic element has an opening.

7. 7. The receiving device of claim 6, wherein the opening has a mesh-like magnetic net connected to the soft magnetic material.

8. 8. The receiving device according to claim 1, wherein when the output voltage from the magnetic element is equal to or greater than a threshold, it is processed as a first signal, and when it is less than the threshold, it is processed as a second signal.

9. A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; receiving the optical signal based on an output voltage from the magnetic element; A receiving device that processes a change in the output voltage from the magnetic element within a predetermined time as a first signal, and a failure of the output voltage from the magnetic element to change within the predetermined time as a second signal.

10. A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; receiving the optical signal based on an output voltage from the magnetic element; Further comprising an integrated circuit; the magnetic element and the integrated circuit are formed on the same substrate with an interlayer insulating film interposed therebetween; the integrated circuit and the magnetic element are connected via a through-wire that penetrates the interlayer insulating film.

11. A receiving device according to any one of claims 1 to 10, A transmitting device that transmits an optical signal.

12. A communication system comprising a plurality of transmitting / receiving devices according to claim 11.

13. A magnetic element comprising a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, light including an optical signal having a change in optical intensity is irradiated onto the first ferromagnetic layer; A portable terminal device having a receiving device that receives the optical signal based on an output voltage from the magnetic element.

14. a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; an output voltage changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer; A light detection element, wherein an angle between the magnetization direction of the first ferromagnetic layer when the first ferromagnetic layer is not irradiated with light and the magnetization direction of the first ferromagnetic layer when the first ferromagnetic layer is irradiated with light is greater than 0° and less than 90°.

15. A magnetic recording medium comprising: a first ferromagnetic layer; a second ferromagnetic layer; and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; an output voltage changes in response to a change in the intensity of the light irradiated to the first ferromagnetic layer; A light signal having at least two levels of intensity is irradiated; When the intensity of the light irradiated to the first ferromagnetic layer is a first intensity, the magnitude of the output voltage has a first value, and when the intensity of the light irradiated to the first ferromagnetic layer is a second intensity, the magnitude of the output voltage has a second value, and the second intensity is greater than the first intensity, when the second value is greater than the first value, a current flows from the first ferromagnetic layer to the second ferromagnetic layer; A photo-sensing element, wherein a current flows from the second ferromagnetic layer to the first ferromagnetic layer when the second value is less than the first value.

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