Photodetector and receiver

Abstract

To provide a light detection element with high light detection capacity.SOLUTION: A light detection element includes: a first ferromagnetic layer to which light is applied; a second ferromagnetic layer; and a spacer layer between the first ferromagnetic layer and the second ferromagnetic layer, the first ferromagnetic layer having a first region in contact with the spacer layer and a second region more distant from the spacer layer than the first region is, the first region being made of a CoFeB alloy and the second region being made of a magnetic body mainly containing Fe and Gd as component elements.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light-sensing element and a receiving device. [Background technology]

[0002] With the spread of the Internet, communication volume has increased dramatically, making optical communication extremely important. Optical communication is a communication method that converts electrical signals into optical signals and transmits and receives them using optical signals.

[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 using a semiconductor pn junction. Furthermore, for example, Patent Document 2 describes an optical sensor using a semiconductor pn junction and an image sensor using this optical sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-292107 [Patent Document 2] U.S. Patent No. 9,842,874 Summary of the Invention [Problem to be solved by the invention]

[0005] Photodetectors using semiconductor pn junctions are widely used, but new photodetectors are needed for further development. Furthermore, photodetectors convert light into electrical signals, and therefore, there is a demand for highly efficient photodetectors with high photodetection capabilities.

[0006] The present invention has been made in view of the above problems, and has an object to provide a photodetector element with high photodetection capability. [Means for solving the problem]

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

[0008] (1) A photodetector according to a first aspect includes a first ferromagnetic layer to which light is irradiated, a second ferromagnetic layer, and a spacer layer sandwiched between the first and second ferromagnetic layers, wherein the first ferromagnetic layer has a first region in contact with the spacer layer and a second region located farther from the spacer layer than the first region, the first region being a CoFeB alloy, and the second region being a magnetic material mainly containing Fe and Gd as constituent elements.

[0009] (2) The light detection element according to the above aspect may further have an intermediate layer between the first region and the second region, and the intermediate layer may contain one or more elements selected from the group consisting of Mo, Ru, Ta, W, and Pt.

[0010] (3) In the photodetector element according to the above aspect, the second ferromagnetic layer has a third region in contact with the spacer layer and a fourth region containing boron that is located farther from the spacer layer than the third region, and the third region may have a lower boron concentration than the fourth region or may not contain boron.

[0011] (4) In the photodetector according to the above aspect, the first region may have a higher boron concentration than the second region.

[0012] (5) In the photodetector according to the above aspect, the third region may contain Fe or a CoFe alloy and have a bcc crystal structure.

[0013] (6) A receiving device according to a second aspect includes the photodetector element according to the above aspect. [Effects of the Invention]

[0014] The light-detecting element according to the above embodiment has high light-detecting ability. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram of a communication system according to a first embodiment. [Figure 2] 1 is a block diagram of a transmission / reception device according to a first embodiment. [Figure 3] 1 is a circuit diagram of a transmitting / receiving device according to a first embodiment. [Figure 4] FIG. 2 is a cross-sectional view of the receiving device according to the first embodiment. [Figure 5] FIG. 2 is a cross-sectional view of the photodetector according to the first embodiment. [Figure 6] 3A and 3B are schematic diagrams illustrating a first mechanism of operation of the light-detecting element according to the first embodiment. [Figure 7] 5A and 5B are schematic diagrams illustrating a second mechanism of operation of the light-detecting element according to the first embodiment. [Figure 8] 4A and 4B are schematic diagrams illustrating a first mechanism of operation of the photodetector in the case where the photodetector according to the first embodiment is used to output multiple values. [Figure 9] 10A and 10B are schematic diagrams illustrating a second mechanism of operation of the photodetector in the case where the photodetector in accordance with the first embodiment is used to output multiple values. [Figure 10] FIG. 1 is a conceptual diagram of another example of a communication system. [Figure 11] FIG. 1 is a conceptual diagram of another example of a communication system. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate changes can be made within the scope of the effects of the present invention.

[0017] 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 the 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.

[0018] "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 together. The communication system 1000 can be used for short- or medium-distance communication, such as within a data center or between data centers, and for long-distance communication, such as between cities. The transmission / reception devices 300 are installed, for example, within a data center. The fiber FB connects, for example, between data centers. The communication system 1000 performs communication between the transmission / reception devices 300 via, for example, the fiber FB. The communication system 1000 may also perform communication between the transmission / reception devices 300 wirelessly, without using the fiber FB.

[0019] 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.

[0020] The receiving device 100 includes, for example, a photodetector element 10 and a signal processing unit 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 processing unit 11 processes the electrical signal converted by the photodetector element 10. The signal processing unit 11 receives the signal included in the optical signal L1 by processing the electrical signal generated from the photodetector element 10.

[0021] 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.

[0022] 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.

[0023] 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 photodetector element 10 in the stacking direction. The first electrode 15 is, for example, the electrode on the side that is irradiated with light including the optical signal L1. The wavelength of the light used for the optical signal L1 is, for example, not less than 300 nm and not more than 2 μm, and the light used for the optical signal L1 may be either visible light or near-infrared light.

[0024] The first electrode 15 is, for example, an input terminal P in and output terminal P out The second electrode 16 is connected to, for example, a reference potential terminal P G Connected to input terminal P in is connected to a power supply PS. The power supply PS may be external to the receiving device 100. The power supply PS applies a sense current or the like to the light detecting element 10. When there is no need to apply a current from an external source to the light detecting element 10, the input terminal P in The power supply PS may be omitted. out outputs the 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 calculated from Ohm's law by passing a sense current through the photodetector element 10 in the stacking direction. outis connected to the signal processing unit 11. The reference potential terminal P 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.

[0025] 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.

[0026] 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.

[0027] The integrated circuit 20 includes a signal processing unit 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 (e.g., "1") when it is equal to or greater than a threshold, and as a second signal (e.g., "0") when it 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. Wire bonding may be used instead of the through-wire w to connect them.

[0028] The interlayer insulating film 30 is an insulator that insulates between wirings in a multilayer wiring structure and between elements. The interlayer insulating film 30 is, for example, an oxide, nitride, or 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.

[0029] Fig. 5 is a cross-sectional view of the photodetector element 10 according to the first embodiment. In Fig. 5, the first electrode 15 and the second electrode 16 are both shown, and the direction of magnetization of the ferromagnetic material in its initial state is indicated by an arrow. In this specification, ferromagnetism includes ferrimagnetism.

[0030] The photodetector element 10 has 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. In addition to these, the photodetector element 10 may also have 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.

[0031] The photodetector element 10 is, for example, an MTJ (Magnetic Tunnel Junction) element in which the spacer layer 3 is made of an insulating material. In this case, the photodetector element 10 is an element in which the resistance value in the z direction (the resistance value when a current is passed in the z direction) changes according to a 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.

[0032] The first ferromagnetic layer 1 is a photodetection layer whose magnetization direction changes when irradiated with external light. The first ferromagnetic layer 1 is also called a magnetization free layer. The magnetization free layer is a layer containing a magnetic material whose magnetization direction changes when a predetermined external force is applied. The predetermined external force is, for example, externally irradiated light, a current flowing in the z direction of the photodetector element 10, or an external magnetic field. The magnetization of a ferromagnetic material can change direction in response to high-speed changes in the intensity of light irradiated onto the ferromagnetic material (high-frequency optical signals). Therefore, by using the first ferromagnetic layer 1 as a photodetection layer, the receiving device 100 can receive high-frequency optical signals, enabling high-speed optical communication.

[0033] The first ferromagnetic layer 1 includes, for example, a first region 1A, a second region 1B, and an intermediate layer 1C. The first region 1A contacts the spacer layer 3. The second region 1B is located farther from the spacer layer 3 than the first region 1A. The intermediate layer 1C is located between the first region 1A and the second region 1B. Each of the first region 1A and the second region 1B extends in a layered manner in, for example, the x direction and the y direction.

[0034] The first region 1A includes a ferromagnetic material. The first region 1A may have a higher boron concentration than the second region 1B, for example. The first region 1A is a CoFeB alloy. When the first region 1A in contact with the spacer layer 3 is a CoFeB alloy, the magnetoresistance change rate (MR change rate) of the photodetector element 10 increases. Therefore, when the first region 1A in contact with the spacer layer 3 is a CoFeB alloy, the output change of the photodetector element 10 in response to a change in the magnetization state of the first region 1A increases. The composition ratio of the CoFeB alloy can be changed as appropriate. For example, the element ratio of the CoFeB alloy is Co:Fe:B=15-55:25-65:15-25, where the sum of Co, Fe, and B is 100.

[0035] The film thickness of the first region 1A is, for example, 5 Å to 20 Å, preferably 8 Å to 15 Å, and more preferably 10 Å. Hereinafter, the film thickness of each layer and each region is defined as the average value of the thickness in the z direction at 10 different points in the xy plane.

[0036] The crystal structure of the CoFeB alloy that constitutes the first region 1A is, for example, a bcc structure.

[0037] The second region 1B is a magnetic material mainly containing Fe and Gd as constituent elements. The second region 1B is, for example, a GdFe alloy, a GdFeCo alloy, a laminated film in which Fe and Gd are laminated, or a laminated film in which an FeCo alloy and Gd are laminated. For example, an example of a GdFe alloy or a GdFeCo alloy is Gd x (Fe 1-y Co y ) 1-xHere, x is, for example, 0.2 or more and 0.3 or less, and y is, for example, 0 or more and 0.2 or less. 1-y Co y / Gd] z Here, y is, for example, 0 or more and 0.2 or less, and z is the number of stacking layers, for example, 4 or more and 10 or less. 1-y Co y The thickness of each layer is, for example, 3.0 Å or more and 8.0 Å or less. The thickness of each Gd layer is, for example, 0.5 Å or more and 3.0 Å or less. The second region 1B may be a single alloy, or may be a laminate of multiple layers made of a single element. The second region 1B has, for example, a total molar fraction of Fe and Gd among its constituent elements of 70% or more.

[0038] The second region 1B is, for example, a perpendicular magnetization film having an easy axis of magnetization in the direction perpendicular to the film surface (z direction). The film thickness of the second region 1B is, for example, 10 Å or more and 200 Å or less. The thickness of the second region 1B may be thicker than that of the first region 1A.

[0039] The crystal structure of the magnetic material containing Fe and Gd that constitutes the second region 1B is, for example, a bcc structure.

[0040] The intermediate layer 1C contains one or more elements selected from the group consisting of Mo, Ru, Ta, W, and Pt. The intermediate layer 1C is a non-magnetic layer. The intermediate layer 1C is made of, for example, Mo, Ru, Ta, W, or Pt. The first region 1A and the second region 1B are magnetically coupled with the intermediate layer 1C sandwiched therebetween. The thickness of the intermediate layer 1C is, for example, 10 Å or less. The thickness of the intermediate layer 1C is, for example, 1 Å or more and 10 Å or less.

[0041] The total thickness of the first ferromagnetic layer 1 is, for example, 1 nm or more and 10 nm or less. The thickness of the first ferromagnetic layer 1 is preferably, for example, 1 nm or more and 5 nm or less. When the thickness of the first ferromagnetic layer 1 is thin, the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is enhanced. By providing the first region 1A in the first ferromagnetic layer 1, even when the first ferromagnetic layer 1 is thin, the MR ratio of the photodetector 10 is improved, and the rate of change in output of the photodetector 10 relative to a change in the magnetization state of the first ferromagnetic layer 1 is improved.

[0042] When the first ferromagnetic layer 1 has the intermediate layer 1C, it is possible to mitigate the influence of the difference in crystal structure between the first region 1A and the second region 1B. The intermediate layer 1C mitigates the difference in crystal structure between the first region 1A and the second region 1B, thereby improving the crystallinity of the second region 1B formed on the intermediate layer 1C.

[0043] In the second region 1B, the magnetic moment of the Fe atom and the magnetic moment of the Gd atom are considered to be ferrimagnetically coupled. The magnetic moment of the Gd atom is easily changed in state by irradiation with light. Therefore, the magnetization of the second region 1B is more easily changed in state by irradiation with light than the magnetization of the first region 1A when the second region 1B is not present alone in the first ferromagnetic layer 1. When the magnetization state of the second region 1B changes, the magnetization state of the first region 1A, which is magnetically coupled to the second region 1B across the intermediate layer 1C, also changes.

[0044] The second ferromagnetic layer 2 is a magnetization fixed layer. The magnetization fixed layer is a layer made of a magnetic material whose magnetization direction is less likely to change when a predetermined external force is applied than the magnetization free layer. The coercive force of the second ferromagnetic layer 2 is, for example, greater than the coercive force of the first ferromagnetic layer 1. The second ferromagnetic layer 2 has an easy axis of magnetization in the same direction as the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be an in-plane magnetization film or a perpendicular magnetization film.

[0045] The second ferromagnetic layer 2 has a third region 2A and a fourth region 2B. The third region 2A is in contact with the spacer layer 3. The fourth region 2B is located farther from the spacer layer 3 than the third region 2A. The third region 2A and the fourth region 2B each extend in a layered shape in the x and y directions, for example.

[0046] The third region 2A includes a ferromagnetic material. The third region 2A may, for example, not include boron or have a lower boron concentration than the fourth region 2B. The third region 2A includes, for example, Fe or a CoFe alloy. The third region 2A may be made of Fe or a CoFe alloy. The crystal structure of the third region 2A may be, for example, a bcc structure. The film thickness of the third region 2A is, for example, 5 Å or more and 10 Å or less. When the second ferromagnetic layer 2 includes the third region 2A, the MR ratio of the photodetector element 10 is improved.

[0047] The fourth region 2B includes a ferromagnetic material. The fourth region 2B may be a single alloy or may be a stack of multiple layers made of a single element. The fourth region 2B may have a higher boron concentration than the third region 2A, for example. The fourth region 2B includes, for example, a CoFeB alloy. The fourth region 2B may have a nonmagnetic insertion layer made of, for example, W or Ta inside. The fourth region 2B may include, for example, Co or a CoFe alloy, a stacked film of Co and Pt, an insertion layer made of Mo or Ta, and a CoFeB alloy, in that order from the side farthest from the spacer layer 3. The film thickness of the fourth region 2B is, for example, 30 Å to 100 Å, and preferably 50 Å to 70 Å.

[0048] 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.

[0049] The third ferromagnetic layer 4 is magnetically coupled to, for example, the second ferromagnetic layer 2. The magnetic coupling is, for example, 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 stacked, or a laminated film in which Co and Ni are alternately stacked. 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 RKKY interaction.

[0050] 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 current-carrying points made of a conductor in an insulator. The thickness of the spacer layer 3 can be adjusted depending on 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, which will be described later.

[0051] For example, if 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. Such an element is called an MTJ element. In this case, the photodetector element 10 can exhibit a tunnel magnetoresistance (TMR) effect. For example, if 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 other names depending on the material of the spacer layer 3, but is also collectively called a magnetoresistance effect element.

[0052] When the spacer layer 3 is made of an insulating material, materials such as aluminum oxide, magnesium oxide, titanium oxide, or silicon oxide can be used. A high magnetoresistance ratio can be obtained by adjusting the thickness of the spacer layer 3 so that a high TMR effect is exhibited between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. To efficiently utilize the TMR effect, the thickness of the spacer layer 3 may be approximately 0.5 to 10.0 nm.

[0053] When the spacer layer 3 is made of a nonmagnetic conductive material, conductive materials 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 3.0 nm.

[0054] When the spacer layer 3 is made of a non-magnetic semiconductor material, it can be made of zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, ITO, etc. In this case, the thickness of the spacer layer 3 may be about 1.0 to 4.0 nm.

[0055] When a layer including current-carrying points formed by a conductor in a nonmagnetic insulator is used as the spacer layer 3, it is preferable to use a structure in which current-carrying points formed by a conductor such as CoFe, CoFeB, CoFeSi, CoMnGe, CoMnSi, CoMnAl, Fe, Co, Au, Cu, Al, or Mg are included in a nonmagnetic insulator made of aluminum oxide or magnesium oxide. In this case, the thickness of the spacer layer 3 may be approximately 0.5 to 2.0 nm. The current-carrying points are, for example, columnar bodies with a diameter of 1 nm to 5 nm.

[0056] 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 improves the crystallinity of the layer stacked 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 alleviates lattice mismatch between different crystals. The buffer layer is, for example, Ta, Ti, W, Zr, Hf, or nitrides of these elements. The buffer layer has a thickness of, for example, 1 nm or more and 5 nm or less.

[0057] The cap layer 8 is located between the first ferromagnetic layer 1 and the first electrode 15 (between the second region 1B and the first electrode 15). The cap layer 8 may include a perpendicular magnetization induction layer 7 stacked on the first ferromagnetic layer 1 and in contact with the first ferromagnetic layer 1. The perpendicular magnetization induction layer 7 induces perpendicular magnetic anisotropy in the first ferromagnetic layer 1. The perpendicular magnetization induction layer 7 is made of, for example, magnesium oxide, W, Ta, or Mo. When the perpendicular magnetization induction layer 7 is made of magnesium oxide, it is preferable that the magnesium oxide has oxygen deficiency to increase conductivity. The film thickness of the perpendicular magnetization induction layer 7 is, for example, 0.5 nm to 5.0 nm. For example, the second region 1B of the first ferromagnetic layer 1 is located between the Mo layer and the intermediate layer 1C. The Mo layer is part of the cap layer 8 and is in contact with the second region 1B. In this case, it is preferable that the thickness of the intermediate layer 1C is thinner than the thickness of the Mo layer that is part of the cap layer 8 and in contact with the second region 1B.

[0058] 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, 10 nm or less so that the first ferromagnetic layer 1 is irradiated with sufficient light.

[0059] 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.

[0060] The first electrode 15 is transparent to light in the wavelength range used by the optical signal L1, for example. The wavelength range used by the light used in the optical signal L1 is, for example, 300 nm or more and 2 μm or less, including the visible light range and the near-infrared light range. The first electrode 15 is a transparent electrode made of, for example, indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium gallium zinc oxide (IGZO), or the like. The first electrode 15 may be configured to have a plurality of metal pillars in a transparent electrode material. The first electrode 15 may also have an anti-reflection film on the irradiation surface onto which light is irradiated.

[0061] The second electrode 16 is made of a conductive material and is, for example, a laminated film of Ta, Ru, and Ta, a laminated film of Ta, Cu, and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN.

[0062] The photodetector 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.

[0063] Next, the laminated film is annealed. The annealing temperature is, for example, 250°C or higher and 400°C or lower. The laminated film is then processed into a predetermined columnar shape by photolithography and etching. The columnar shape may be a circular column or a rectangular column. For example, the minimum width of the columnar shape when viewed from the z direction is 10 nm or higher and 1000 nm or lower.

[0064] Next, an insulating layer is formed to cover the side surfaces of the pillars. This insulating layer becomes the sidewall insulating layer 9. The sidewall insulating layer 9 may be stacked multiple times. Next, the upper surface of the cap layer 8 is exposed from the sidewall insulating layer 9 by chemical mechanical polishing, and a first electrode 15 is formed on the cap layer 8. Through the above process, the photodetector element 10 is obtained.

[0065] Next, an example of the operation of the photodetector 10 according to the first embodiment will be described. The first ferromagnetic layer 1 is irradiated with light containing an optical signal L1 having a change in optical intensity. The output voltage from the photodetector 10 in the z direction changes when the first ferromagnetic layer 1 is irradiated with light containing 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 intensity of the light with the second intensity is assumed to be greater than the intensity of the light with the first intensity. The first intensity may be zero when the intensity of the light irradiated to the first ferromagnetic layer 1 is zero.

[0066] 6 and 7 are diagrams illustrating an example of the operation 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 illustrating the first mechanism, and FIG. 7 is a diagram illustrating the second mechanism. In the upper graphs of FIGS. 6 and 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 FIGS. 6 and 7, the vertical axis represents the resistance value of the photodetector 10 in the z direction, and the horizontal axis represents time.

[0067] First, in a state where the first ferromagnetic layer 1 is irradiated with light of a first intensity (hereinafter referred to as the initial state), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are parallel, the resistance value of the photodetector element 10 in the z direction exhibits a first resistance value R1, and the magnitude of the output voltage from the photodetector element 10 exhibits a first value. The resistance value of the photodetector element 10 in the z direction is calculated using Ohm's law by flowing a sense current Is in the z direction of the photodetector element 10, generating a voltage across both ends of the photodetector element 10 in the z direction. The output voltage from the photodetector element 10 is generated between the first electrode 15 and the second electrode 16. In the example shown in FIG. 6, the sense current Is is flowed 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 acts on the magnetization M1 of the first ferromagnetic layer 1 in the same direction as the magnetization M2 of the second ferromagnetic layer 2, and the magnetizations M1 and M2 become parallel in the initial state. Also, 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.

[0068] 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 its initial state. The state of the magnetization M1 refers to, 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 when 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 less 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 its 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. The second resistance value R2 is greater than the first resistance value R1. 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.

[0069] The magnetization M1 of the first ferromagnetic layer 1 is subjected to a spin transfer torque 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, which is tilted from the initial state, attempts to return to a state parallel to the magnetization M2. When the intensity of the light irradiating the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the photodetector element 10 returns to its initial state. In the case shown in FIG. 7, when the intensity of the light irradiating 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 element 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 element 10 returns to the first resistance value R1. In other words, when the intensity of the light irradiating 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.

[0070] In either mechanism, the resistance value in the stacking direction of the photodetector element 10 changes in response to changes in the intensity of light irradiated onto the first ferromagnetic layer 1, and changes in the intensity of the optical signal L1 can be converted into changes in the resistance value in the z direction of the photodetector element 10. Furthermore, the output voltage from the photodetector element 10 changes in response to changes in the intensity of light irradiated onto the first ferromagnetic layer 1, and changes in the intensity of the optical signal L1 can be converted into changes in the output voltage from the photodetector element 10. The output from the photodetector element 10 is sent to a signal processing unit 11, which processes the output as a first signal (e.g., "1") if it is equal to or greater than a threshold, or as a second signal (e.g., "0") if it is less than the threshold.

[0071] 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 element 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.

[0072] 8 and 9 show the behavior of the photodetector 10 according to the first embodiment when it outputs multiple values. FIG. 8 is a diagram illustrating the first mechanism, and FIG. 9 is a diagram illustrating the second mechanism. FIGS. 8 and 9 show the magnetization states and resistance values ​​in the z direction of the photodetector 10 at first, second, third, and fourth intensities, respectively, from left to right. The intensities of light irradiated onto the first ferromagnetic layer 1 increase in order from the fourth intensity to the third intensity, the second intensity, and the first intensity.

[0073] As shown in FIG. 8 , when the magnetization M1 tilts depending on the intensity of the irradiated light, the angle change of the magnetization M1 from the initial state increases as the intensity of the light irradiated to the first ferromagnetic layer 1 increases. When the first ferromagnetic layer 1 is not irradiated with light including the optical signal L1, the angle change of each of the second intensity, third intensity, and fourth intensity with respect to the direction of the magnetization M1 of the first ferromagnetic layer 1 is greater than 0° and less than 90°. The change in the resistance value of the photodetector 10 in the z direction from the initial state increases as the angle change of the magnetization M1 from the initial state increases. Therefore, the resistance value of the photodetector 10 in the z direction differs for each of the first intensity, second intensity, third intensity, and fourth intensity. The photodetector 10 according to the first embodiment can read out four values ​​of information, for example, “0,” “1,” “2,” and “3,” by defining the threshold value of the output voltage (resistance threshold value) in multiple stages. Here, an example is shown in which four values ​​are read out, but the number of values ​​to be read out can be freely designed by setting the threshold value of the output voltage (threshold value of the resistance).

[0074] 9, as the intensity of light irradiated onto the first ferromagnetic layer 1 increases, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 decreases from its initial state due to external energy from the light irradiation. When the magnetization M1 of the first ferromagnetic layer 1 decreases from its initial state, the resistance value in the z direction of the photodetector element 10 changes. For example, depending on the magnitude of the magnetization M1 of the first ferromagnetic layer 1, 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. Therefore, as in the case of FIG. 8, the difference in output voltage from the photodetector element 10 can be output as multi-value or analog data.

[0075] As described above, the photodetector 10 according to the first embodiment converts an optical signal into an electrical signal.

[0076] The photodetector element 10 has a large magnetoresistance change rate (MR change rate) because the first region 1A in contact with the spacer layer 3 is a CoFeB alloy. Therefore, the photodetector element 10 has a large change in output in response to a change in the magnetization state of the first region 1A.

[0077] Furthermore, since the photodetector element 10 has a second region 1B that is a magnetic material containing Fe and Gd, the magnetization state of the second region 1B changes even when irradiated with a small amount of light, and the magnetization state of the first region 1A that is magnetically coupled to the second region 1B also changes.

[0078] Therefore, the output of the photodetector 10 changes greatly in response to changes in the amount of light irradiated thereto. As such, the photodetector 10 according to the first embodiment has a high efficiency in converting optical signals into electrical signals and a high light detection capability.

[0079] In the first embodiment, the first ferromagnetic layer 1 includes the first region 1A, thereby improving the MR ratio of the photodetector 10. Furthermore, the second ferromagnetic layer 2 includes the third region 2A, thereby improving the MR ratio of the photodetector 10. While there is a demand for a thinner first ferromagnetic layer 1 to improve the response characteristics of the photodetector 10 to light, the MR ratio of the photodetector 10 can be increased even within these constraints by including the first region 1A and the third region 2A in the photodetector 10. As a result, the change in the resistance value of the photodetector 10 (the change in the voltage output from the photodetector 10) in response to a change in the light intensity of the optical signal L1 can be increased. This increases the sensitivity of the photodetector 10, allowing the photodetector 10 to be used in a receiving device 100 that enables high-speed communication.

[0080] Although the example in which the transmitting / receiving device is applied to the communication system 1000 shown in FIG. 1 has been shown up to this point, the communication system is not limited to this case.

[0081] For example, Fig. 10 is a conceptual diagram of another example of a communication system. A communication system 1001 shown in Fig. 10 is communication between two mobile terminal devices 500. The mobile terminal devices 500 are, for example, smartphones, tablets, etc.

[0082] 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. The light used for transmission and reception between the mobile terminal devices 500 is, for example, visible light. The above-described photodetector element is applied as the photodetector element 10 of each receiving device 100.

[0083] 11 is a conceptual diagram of another example of a communication system. A communication system 1002 shown in Fig. 11 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.

[0084] 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. The light used for transmission and reception between the mobile terminal device 500 and the information processing device 600 is, for example, visible light. The above-described photodetector element is applied as the photodetector element 10 of each receiving device 100.

[0085] As described above, the present invention is not limited to the above-described embodiments and modifications, and various modifications and changes are possible within the scope of the gist of the present invention as defined in the claims.

[0086] Although the photodetector element according to the present invention is used in a receiving device, the present invention is not limited to this example. For example, the photodetector element according to the present invention can be used in place of various semiconductor photodetectors such as an image sensor. [Example]

[0087] Example 1 The second electrode, underlayer, and second ferromagnetic layer were deposited on the substrate in this order using targets of each material. The second electrode consisted of, from the substrate side, 50 Å thick Ta, 600 Å thick Ru, and 100 Å thick Ta. The underlayer consisted of, from the substrate side, 20 Å thick Ta and 20 Å thick Pt. The second ferromagnetic layer consisted of, from the substrate side, a laminated film consisting of 5 Å thick Co and 4 Å thick Pt alternately stacked four times, 6 Å thick Co, 8 Å thick Ru, 6 Å thick Co, 4 Å thick Pt and 5 Å thick Co alternately stacked three times, 4 Å thick Mo, 6 Å thick CoFeB, and 5 Å thick Fe.

[0088] Next, a Mg film was formed, and then an oxidation treatment was performed in an oxidation chamber to form a spacer layer of MgO with a thickness of 12 Å. 0.65 B 0.35 Target and Fe 0.65 B 0.35 Co-sputtering (two-target simultaneous sputtering) was performed using a Gd target and an Fe target, and the first region of the first ferromagnetic layer was deposited to a thickness of 10 Å. Next, a Mo film was deposited to a thickness of 5 Å as the intermediate layer. Next, co-sputtering (two-target simultaneous sputtering) was performed on the intermediate layer using a Gd target and an Fe target, and the second region of the first ferromagnetic layer was deposited to a thickness of 25 Å.

[0089] A cap layer was then formed on the first ferromagnetic layer. The cap layers were, in order from the substrate side, 20 Å thick Mo, 20 Å thick Ta, and 20 Å thick Ru. Annealing was then performed in vacuum at 400°C for 30 minutes. A first electrode was then formed on the annealed stack and processed into a cylindrical shape with a diameter of 300 nm to produce a photodetector. The first electrode was made of indium tin oxide (ITO) with a thickness of 500 Å. Each layer was formed using a DC magnetron sputtering device.

[0090] The element configuration of the photodetector element fabricated in Example 1 is summarized below. 2nd electrode: Ta(50Å) / Ru(600Å) / Ta(100Å) Base layer: Ta(20Å) / Pt(20Å) Second ferromagnetic layer: [Co(5Å) / Pt(4Å)]4 / Co(6Å) / Ru(8Å) / Co(6Å) / [Pt(4Å) / Co(5Å)]3 / Mo(4Å) / CoFeB(6Å) / Fe(5Å) Spacer layer: MgO (12 Å) First ferromagnetic layer: Co 0.24 Fe 0.56 B 0.20 (10Å) / Mo(5Å) / Gd 0.26 Fe 0.74 (25Å) Capping layer: Mo (20 Å) / Ta (20 Å) / Ru (20 Å) 1st electrode: ITO (500Å)

[0091] The fabricated photodetector was irradiated with pulsed light from the first electrode side. A 50 mW short-pulse laser (wavelength 800 nm) was used as the light source. The light pulse width was 50 fsec, the light spot diameter was 2 mm, and the intensity of the 50 mW pulsed light was reduced to 1 / 1000 before irradiating the photodetector. A direct current of 0.25 mA was applied to the photodetector. Then, the change in output voltage from the photodetector caused by irradiating the photodetector with pulsed light was measured using a high-speed oscilloscope. The change in output voltage from the photodetector according to Example 1 before and after irradiation with pulsed light was 5.0 mV.

[0092] Example 2 Example 2 differs from Example 1 in that the configuration of the second region of the first ferromagnetic layer was changed. In Example 2, co-sputtering (three-target simultaneous sputtering) was performed on the intermediate layer using a Gd target, an Fe target, and a Co target to form the second region of the first ferromagnetic layer to a thickness of 25 Å.

[0093] The layer structure of the first ferromagnetic layer in Example 2 is as follows, and the structures of the other layers are the same as those in Example 1. First ferromagnetic layer: Co 0.24 Fe 0.56 B 0.20 (10Å) / Mo(5Å) / Gd 0.26 (Fe 0.90 Co 0.10 ) 0.74 (25Å)

[0094] In Example 2, pulsed light was irradiated and the change in output voltage before and after irradiation was measured in the same manner as in Example 1. The change in output voltage before and after pulsed light irradiation in the photodetector according to Example 2 was 4.8 mV.

[0095] Example 3 Example 3 differs from Example 1 in that the configuration of the second region of the first ferromagnetic layer was changed. In Example 3, the second region of the first ferromagnetic layer was formed by alternately stacking five layers of Fe with a thickness of 3.7 Å and five layers of Gd with a thickness of 1.3 Å on the intermediate layer.

[0096] The layer structure of the first ferromagnetic layer in Example 3 is as follows, and the structures of the other layers are the same as those in Example 1. First ferromagnetic layer: Co 0.24 Fe 0.56 B 0.20 (10Å) / Mo(5Å) / [Fe(3.7Å) / Gd(1.3Å)]5

[0097] In Example 3, pulsed light was irradiated and the change in output voltage before and after irradiation was measured in the same manner as in Example 1. The change in output voltage before and after pulsed light irradiation in the photodetector according to Example 3 was 9.8 mV.

[0098] Example 4 Example 4 differs from Example 1 in that the configuration of the second region of the first ferromagnetic layer was changed. In Example 4, the second region of the first ferromagnetic layer was formed by alternately stacking five layers of an FeCo alloy film with a thickness of 3.7 Å and a Gd film with a thickness of 1.3 Å on the intermediate layer. The FeCo alloy film was formed by co-sputtering (two-target simultaneous sputtering) using an Fe target and a Co target.

[0099] The layer structure of the first ferromagnetic layer in Example 4 is as follows, and the structures of the other layers are the same as those in Example 1. First ferromagnetic layer: Co 0.24 Fe 0.56 B 0.20 (10Å) / Mo(5Å) / [Fe 0.90 Co 0.10(3.7Å) / Gd(1.3Å)]5

[0100] In Example 4, pulsed light was irradiated and the change in output voltage before and after irradiation was measured in the same manner as in Example 1. The change in output voltage before and after pulsed light irradiation in the photodetector according to Example 4 was 10.0 mV.

[0101] (Comparative Example 1) Comparative Example 1 differs from Example 1 in that the configuration of the first ferromagnetic layer was changed. In Comparative Example 1, unlike Example 1, the intermediate layer and second region of the first ferromagnetic layer 1 were not formed.

[0102] The layer structure of the first ferromagnetic layer in Comparative Example 1 is as follows, and the structures of the other layers were the same as those in Example 1. First ferromagnetic layer: Co 0.24 Fe 0.56 B 0.20 (10Å)

[0103] In Comparative Example 1, pulsed light was irradiated and the change in output voltage before and after irradiation was measured in the same manner as in Example 1. The change in output voltage before and after pulsed light irradiation in the photodetector of Comparative Example 1 was 2.5 mV.

[0104] The results of Examples 1 to 4 and Comparative Example 1 are summarized in the table below. As shown in Table 1, the photodetectors of Examples 1 to 4 had higher efficiency of converting optical signals into electrical signals than the photodetector of Comparative Example 1.

[0105] [Table 1] [Explanation of symbols]

[0106] 1...first ferromagnetic layer, 1A...first region, 1B...second region, 1C...intermediate layer, 2...second ferromagnetic layer, 2A...third region, 2B...fourth region, 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, 11...signal processing unit, 15...first electrode, 16...second electrode, 20...integrated circuit, 30...interlayer insulating film, 100...receiving device, 200...transmitting device, 201...light source, 202...electrical signal generating element, 203...light modulation element, 300...transmitting / receiving device, 500...portable terminal device, 600...information processing device, 1000, 1001, 1002...communication system, FB...fiber, G...ground, Is...sense current, M1, M2...magnetization, P G ...Reference potential terminal, P in …input terminal, P out ...Output terminal, PS...Power supply, w...Through-through wiring

Claims

1. a first ferromagnetic layer to be irradiated with light, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; the first ferromagnetic layer has a first region in contact with the spacer layer and a second region located farther from the spacer layer than the first region; the first region is a CoFeB alloy, and the second region is a magnetic material containing mainly Fe and Gd as constituent elements, with the total molar fraction of Fe and Gd being 70% or more; the second ferromagnetic layer is a magnetization fixed layer having a coercive force greater than that of the first ferromagnetic layer, A light-sensing element, wherein an output voltage changes in response to a change in the intensity of light irradiated onto a first ferromagnetic layer when the first ferromagnetic layer is irradiated with light.

2. further comprising an intermediate layer between the first region and the second region; The light-sensing element according to claim 1 , wherein the intermediate layer contains at least one element selected from the group consisting of Mo, Ru, Ta, W, and Pt.

3. the second ferromagnetic layer has a third region in contact with the spacer layer and a fourth region containing boron and located farther from the spacer layer than the third region; 3. The light-detecting element according to claim 1, wherein the third region has a lower concentration of boron than the fourth region, or does not contain boron.

4. 4. The light-detecting element according to claim 1, wherein the first region has a higher concentration of boron than the second region.

5. The photo-sensing element according to claim 3 , wherein the third region contains Fe or a CoFe alloy and has a bcc crystal structure.

6. When the magnetization of the first ferromagnetic layer and the magnetization of the second ferromagnetic layer are parallel in a state where no light is irradiated, a sense current is caused to flow from the first ferromagnetic layer to the second ferromagnetic layer; A light-sensing element according to any one of claims 1 to 5, configured to flow a sense current from the second ferromagnetic layer toward the first ferromagnetic layer when the magnetization of the first ferromagnetic layer and the magnetization of the second ferromagnetic layer are antiparallel in the absence of light irradiation.

7. A receiving device comprising a photodetector element according to any one of claims 1 to 6.

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