Light detecting element and receiving device

Abstract

The light detecting element of the present application includes a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer interposed between the first and second ferromagnetic layers, the first ferromagnetic layer having a first region in contact with the spacer layer and a second region located further from the spacer layer than the first region, the first region being a CoFeB alloy, and the second region being a magnetic body mainly containing Fe and Gd as constituent elements.

Description

Technical Field

[0001] The present invention relates to a light detecting element and a receiving device. Background Art

[0002] With the widespread use of the Internet, communication volume has increased dramatically, and optical communications have become extremely important. Optical communications is a communication method that converts electrical signals into optical signals and uses them for transmission and reception.

[0003] For example, Patent Document 1 describes a receiving device that uses a photodiode to receive light signals. A photodiode is, for example, a PN junction diode using a semiconductor. Furthermore, Patent Document 2 describes a photosensor using a semiconductor PN junction and an image sensor using the photosensor.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-292107

[0007] Patent Document 2: U.S. Patent No. 9,842,874 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] Photodetectors using semiconductor PN junctions are widely used, but further development requires new photodetectors. Photodetectors convert light into electrical signals, and high light detection capabilities with high efficiency are required.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a light detecting element having high light detecting capability.

[0011] Technical solutions to solve problems

[0012] In order to solve the above problems, the following solutions are provided.

[0013] (1) A light detecting element of the first type comprises: a first ferromagnetic layer irradiated with light, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, wherein the first ferromagnetic layer has: a first region relative to the spacer layer, and a second region located further away from the spacer layer than the first region, the first region being a CoFeB alloy, and the second region being a magnetic body mainly containing Fe and Gd as constituent elements.

[0014] (2) The light detecting element of the above aspect may further include an intermediate layer between the first region and the second region, wherein the intermediate layer contains at least one element selected from the group consisting of Mo, Ru, Ta, W, and Pt.

[0015] (3) The light detection element of the above-mentioned method may also be that the second ferromagnetic layer has: a third region connected to the spacer layer, and a fourth region located at a position farther away from the spacer layer than the third region and containing boron, and the third region has a lower boron concentration than the fourth region, or does not contain boron.

[0016] (4) In the light detecting element according to the above aspect, the first region may have a higher boron concentration than the second region.

[0017] (5) In the above-described light detecting element, the third region may contain Fe or a CoFe alloy and have a bcc crystal structure.

[0018] (6) A receiving device according to a second aspect includes a light detecting element according to the above aspect.

[0019] Effects of the Invention

[0020] The light detecting element of the above-described embodiment has high light detecting capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a conceptual diagram of the communication system according to the first embodiment.

[0022] Figure 2 This is a block diagram of the transceiver according to the first embodiment.

[0023] Figure 3 This is a circuit diagram of the transceiver according to the first embodiment.

[0024] Figure 4 It is a cross-sectional view of the receiving device of the first embodiment.

[0025] Figure 5 This is a cross-sectional view of the light detecting element according to the first embodiment.

[0026] Figure 6 This is a schematic diagram for explaining a first mechanism of operation of the light detecting element according to the first embodiment.

[0027] Figure 7 This is a schematic diagram for explaining a second mechanism of the operation of the photodetection element according to the first embodiment.

[0028] Figure 8 This is a schematic diagram for explaining a first mechanism of operation of the photodetection element when the photodetection element according to the first embodiment outputs multiple values.

[0029] Figure 9 This is a schematic diagram for explaining a second mechanism of operation of the photodetection element when the photodetection element according to the first embodiment outputs multiple values.

[0030] Figure 10 This is a conceptual diagram of another example of a communication system.

[0031] Figure 11 This is a conceptual diagram of another example of a communication system.

[0032] Explanation of symbols

[0033] 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…Base layer, 7…Perpendicular magnetization inducing 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…Receiver, 200…Transmitter, 201…Light source, 202…Electrical signal generating element, 203…Optical modulator, 300…Transmitter / receiver, 500…Mobile terminal device, 600…Information processing device, 1000, 1001, 1002…Communication system, FB…Optical 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 wiring DETAILED DESCRIPTION

[0034] The following embodiments are described in detail with reference to the accompanying drawings as appropriate. In the drawings used in the following description, for ease of understanding, sometimes featured portions are enlarged, and the dimensional ratios of various components may differ from actual dimensions. The materials, dimensions, and other aspects illustrated in the following description are merely examples, and the present invention is not limited to these. These embodiments may be modified as appropriate within the scope of achieving the effects of the present invention.

[0035] Define the direction. Let the stacking direction of the light detection element 10 be the z direction, the direction within the plane perpendicular to the z direction be the x direction, and the direction perpendicular to the x and z directions be the y direction. The z direction is an example of a stacking direction. Hereinafter, the +z direction may be represented as "up" and the -z direction as "down." The +z direction is the direction from the substrate Sb toward the light detection element 10. Up and down do not necessarily coincide with the direction in which gravity is applied.

[0036] "First Implementation Method"

[0037] Figure 1 This is a conceptual diagram of the communication system 1000 according to the first embodiment. Figure 1 The illustrated communication system 1000 includes a plurality of transceivers 300 and an optical fiber FB connecting the transceivers 300. The communication system 1000 can be used, for example, for short- and medium-distance communications within and between data centers, as well as for long-distance communications between cities. The transceivers 300 are, for example, installed within a data center. The optical fiber FB connects, for example, data centers. The communication system 1000 communicates between the transceivers 300, for example, via the optical fiber FB. Alternatively, the communication system 1000 can communicate between the transceivers 300 wirelessly, rather than via the optical fiber FB.

[0038] Figure 2 This is a block diagram of a transceiver 300 according to the first embodiment. Transceiver 300 includes a receiver 100 and a transmitter 200. Receiver 100 receives optical signal L1, and transmitter 200 transmits optical signal L2. The term "light" in this specification is not limited to visible light but also includes infrared light with a longer wavelength than visible light and ultraviolet light with a shorter wavelength than visible light.

[0039] The receiving device 100 includes, for example, a photodetection element 10 and a signal processing unit 11. The photodetection element 10 converts the optical signal L1 into an electrical signal. The photodetection element 10 will be described in detail later. The signal processing unit 11 processes the electrical signal converted by the photodetection element 10. By processing the electrical signal generated by the photodetection element 10, the signal processing unit 11 receives a signal included in the optical signal L1.

[0040] Transmitting device 200 includes, for example, a light source 201, an electrical signal generating element 202, and an optical modulator 203. Light source 201 is, for example, a laser element. Light source 201 may also be external to transmitting device 200. Electrical signal generating element 202 generates an electrical signal based on transmission information. Electrical signal generating element 202 may also be integrated with the signal conversion element of signal processing unit 11. Optical modulator 203 modulates the light output from light source 201 based on the electrical signal generated by electrical signal generating element 202, and outputs optical signal L2.

[0041] Figure 3 FIG. 1 is a circuit diagram of the transceiver 300 according to the first embodiment. Figure 3 , the signal processing unit 11 is omitted.

[0042] The receiving device 100 includes, for example, a light detecting element 10, a first electrode 15, a second electrode 16, an input terminal P in , output terminal P out , and the reference potential terminal P GThe first electrode 15 and the second electrode 16 sandwich the light detecting element 10 in the stacking direction. The first electrode 15 is, for example, the electrode on the side irradiated with light including the light signal L1. The wavelength of the light used for the light signal L1 is, for example, greater than 300 nm and less than 2 μm. The light used for the light signal L1 may be visible light or near-infrared light.

[0043] The first electrode 15 is connected to the input terminal P in And output terminal P out The second electrode 16 is connected to the reference potential terminal P G Connection. Input terminal P in Connected to the power supply PS. The power supply PS can also be located outside the receiving device 100. The power supply PS applies a sensing current to the light detection element 10. If it is not necessary to allow current to flow from the outside to the light detection element 10, the input terminal P can be removed. in And power supply PS. Output terminal P out Outputs the voltage between the first electrode 15 and the second electrode 16 that sandwich the light detection element 10 in the stacking direction. The resistance value of the light detection element 10 in the stacking direction is obtained by flowing a sense current in the stacking direction of the light detection element 10 according to Ohm's law. Output terminal P out Connected to the signal processing unit 11. Reference potential terminal P G It is connected to the reference potential and determines the reference potential of the receiving device 100 . Figure 3 The reference potential in the example is ground G. Ground G may be provided outside the receiving device 100. The reference potential may be other than ground G.

[0044] The receiving device 100 and the transmitting device 200 are connected to a common reference potential (ground G), for example. The reference potentials of the receiving device 100 and the transmitting device 200 may be different. When the reference potentials of the receiving device 100 and the transmitting device 200 are the same, the generation of noise can be reduced.

[0045] Figure 4 1 is a cross-sectional view of a receiving device 100 according to the first embodiment. The receiving device 100 includes, for example, a light detecting element 10, an integrated circuit 20, and an interlayer insulating film 30. The light detecting element 10, the integrated circuit 20, and the interlayer insulating film 30 are formed on, for example, the same substrate Sb.

[0046] The integrated circuit 20 includes a signal processing unit 11 that processes the signal output from the light detection element 10. The integrated circuit 20 processes the case where the output voltage from the light detection element 10 (the resistance value in the z direction of the light detection element 10) is above a threshold value as a first signal (for example, "1"), and the case where it is below the threshold value as a second signal (for example, "0"). In the case where the transmitting device 200 is formed on the same substrate Sb, the integrated circuit 20 may also include a light source 201, an electric signal generating element 202, and a light modulation element 203. The integrated circuit 20 and the light detection element 10 are connected, for example, via a through wiring w that penetrates the interlayer insulating film 30. The through wiring w may also be changed to connect them by wire bonding.

[0047] The interlayer insulating film 30 is an insulator that insulates the wirings and components of the multilayer wiring. 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, 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 )wait.

[0048] Figure 5 : is a cross-sectional view of the light detecting element 10 according to the first embodiment. Figure 5 , the first electrode 15 and the second electrode 16 are shown together, and the magnetization direction of the ferromagnetic body in the initial state is indicated by arrows. In this specification, ferromagnetism includes ferrimagnetism.

[0049] The light detecting element 10 includes 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 layers, the light detecting element 10 may further include a third ferromagnetic layer 4, a magnetic coupling layer 5, a base layer 6, a perpendicular magnetization inducing layer 7, a cap layer 8, and a sidewall insulating layer 9.

[0050] The light detecting 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 light detecting element 10 changes its resistance in the z direction (the resistance when current flows in the z direction) based on the relative angle between the magnetization directions of the first ferromagnetic layer 1 and the second ferromagnetic layer 2. This type of element is also called a magnetoresistive element.

[0051] 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 containing a magnetic body whose magnetization direction changes when a predetermined external force is applied. The predetermined external force is, for example, light irradiated from the outside, a current flowing along the z direction of the light detection element 10, or an external magnetic field. The magnetization of the ferromagnetic body can change direction by following the high-speed change in the intensity of the light irradiated on the ferromagnetic body (high-frequency light signal). Therefore, by using the first ferromagnetic layer 1 as a light detection layer, the receiving device 100 can receive high-frequency light signals, making high-speed optical communication possible.

[0052] 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 is in contact with 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, for example, in the x-direction and the y-direction.

[0053] The first region 1A contains a ferromagnetic material. The first region 1A may also 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 light detecting element 10 becomes larger. Therefore, when the first region 1A in contact with the spacer layer 3 is a CoFeB alloy, the output change of the light detecting element 10 relative to the change in the magnetization state of the first region 1A becomes larger. The composition ratio of the CoFeB alloy can be appropriately changed. For example, under the condition that the total of Co, Fe, and B is 100, the element ratio of the CoFeB alloy is Co:Fe:B = 15 to 55:25 to 65:15 to 25.

[0054] The film thickness of the first region 1A is, for example, Above and The following are preferably Above and The following are more preferably Hereinafter, the film thickness of each layer and the film thickness of each region are defined as the average value of the thickness in the z direction at 10 different points in the xy plane.

[0055] The crystal structure of the CoFeB alloy constituting the first region 1A is, for example, a bcc structure.

[0056] The second region 1B is a magnetic body mainly containing Fe and Gd as constituent elements. The second region 1B is, for example, a GdFe alloy, a GdFeCo alloy, a laminated film of Fe and Gd, or a laminated film of FeCo alloy and Gd. For example, as an example of a GdFe alloy or a GdFeCo alloy, a GdFeCo alloy having Gd x(Fe 1-y Co y ) 1-x Here, x is, for example, greater than or equal to 0.2 and less than or equal to 0.3, and y is, for example, greater than or equal to 0 and less than or equal to 0.2. In addition, as an example of a laminated film, a film having [Fe 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 the layer is, for example, Above and The thickness of each Gd layer is, for example, Above and The second region 1B may be a single alloy or a laminate of multiple layers composed of a single element. The total molar fraction of Fe and Gd in the constituent elements of the second region 1B is, for example, 70% or more.

[0057] The second region 1B is, for example, a perpendicular magnetization film having an easy magnetization axis in the normal direction (z direction) of the film. The film thickness of the second region 1B is, for example, Above and The second region 1B is thicker than the first region 1A.

[0058] The crystal structure of the magnetic material containing Fe and Gd constituting the second region 1B is, for example, a bcc structure.

[0059] The intermediate layer 1C contains at least one element selected from Mo, Ru, Ta, W, and Pt. The intermediate layer 1C is a non-magnetic layer. The intermediate layer 1C is composed of, for example, any one of Mo, Ru, Ta, W, and Pt. The first region 1A and the second region 1B are magnetically coupled by sandwiching the intermediate layer 1C. The thickness of the intermediate layer 1C is, for example, The thickness of the intermediate layer 1C is, for example, Above and the following.

[0060] The overall thickness of the first ferromagnetic layer 1 is, for example, not less than 1 nm and not more than 10 nm. The thickness of the first ferromagnetic layer 1 is preferably, for example, not less than 1 nm and not more than 5 nm. When the first ferromagnetic layer 1 is thin, the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high. Providing the first region 1A in the first ferromagnetic layer 1 improves the MR ratio of the light detecting element 10 even when the first ferromagnetic layer 1 is thin, and also improves the ratio of the output change of the light detecting element 10 to the change in the magnetization state of the first ferromagnetic layer 1.

[0061] When the first ferromagnetic layer 1 includes the intermediate layer 1C, the effect of the difference in crystal structure between the first region 1A and the second region 1B can be mitigated. 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.

[0062] Consider the following: The magnetic moments of the Fe atoms in the second region 1B are ferrimagnetically coupled to the magnetic moments of the Gd atoms. The magnetic moments of the Gd atoms are susceptible to changes in state in response to light. Therefore, the magnetization of the second region 1B is more susceptible to changes in state in response to light than the magnetization of the first region 1A alone, without the second region 1B in the first ferromagnetic layer 1. When the magnetization of the second region 1B changes, the magnetization of the first region 1A, which is magnetically coupled to the second region 1B via the intermediate layer 1C, also changes.

[0063] The second ferromagnetic layer 2 is a fixed magnetization layer. The fixed magnetization layer is composed of a magnetic material whose magnetization direction is less susceptible to change than that of the free magnetization layer when a predetermined external force is applied. The coercive force of the second ferromagnetic layer 2 is, for example, greater than that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 has an easy magnetization axis in the same direction as that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 can be an in-plane magnetization film or a perpendicular magnetization film.

[0064] The second ferromagnetic layer 2 includes 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. Each of the third region 2A and the fourth region 2B extends in a layered manner, for example, in the x-direction and the y-direction.

[0065] The third region 2A contains a ferromagnetic material. The third region 2A may not contain boron or may have a lower boron concentration than the fourth region 2B. The third region 2A may contain Fe or a CoFe alloy. The third region 2A may also be composed of Fe or a CoFe alloy. The crystal structure of the third region 2A may also be a bcc structure. The film thickness of the third region 2A may be, for example, Above and When the second ferromagnetic layer 2 includes the third region 2A, the MR ratio of the light detecting element 10 is improved.

[0066] The fourth region 2B contains a ferromagnetic material. The fourth region 2B may be a single alloy or a material in which multiple layers composed of a single element are stacked. The boron concentration of the fourth region 2B may be higher than that of the third region 2A, for example. The fourth region 2B may contain a CoFeB alloy, for example. The fourth region 2B may also have a non-magnetic insertion layer composed of, for example, W or Ta inside. The fourth region 2B may also have, for example, a stacked film of Co or CoFe alloy, Co and Pt, an insertion layer composed of Mo and Ta, and a CoFeB alloy in sequence from the side away from the spacer layer 3. The film thickness of the fourth region 2B may be, for example, Above and The following are preferably Above and the following.

[0067] The magnetization of the second ferromagnetic layer 2 may be fixed by magnetic coupling with the third ferromagnetic layer 4 via the magnetic coupling layer 5. In this case, the layer combining the second ferromagnetic layer 2, the magnetic coupling layer 5, and the third ferromagnetic layer 4 is sometimes referred to as a magnetization fixed layer.

[0068] The third ferromagnetic layer 4 is, for example, magnetically coupled to the second ferromagnetic layer 2. This magnetic coupling is, for example, antiferromagnetic and occurs through the RKKY interaction. The third ferromagnetic layer 4 is made of, for example, the same material as the first ferromagnetic layer 1. For example, the third ferromagnetic layer 4 is a laminated film of alternating layers of Co and Pt, or a laminated film of alternating layers of Co and Ni. The magnetic coupling layer 5 is, for example, made of Ru, Ir, or the like. The film thickness of the magnetic coupling layer 5 is, for example, such that the second ferromagnetic layer 2 and the third ferromagnetic layer 4 are antiferromagnetically coupled through the RKKY interaction.

[0069] Spacer layer 3 is a nonmagnetic layer positioned between first ferromagnetic layer 1 and second ferromagnetic layer 2. Spacer layer 3 is composed of a layer made of a conductor, an insulator, or a semiconductor, or a layer containing a conductive point within an insulator. The thickness of spacer layer 3 can be adjusted based on the orientation of the magnetization M1 of first ferromagnetic layer 1 and the magnetization M2 of second ferromagnetic layer 2 in the initial state, as described later.

[0070] For example, when the spacer layer 3 is composed of an insulator, the light detecting element 10 has a magnetic tunnel junction (MTJ) composed of the first ferromagnetic layer 1, the spacer layer 3, and the second ferromagnetic layer. This element is called an MTJ element. In this case, the light detecting element 10 can embody the tunnel magnetoresistance (TMR) effect. For example, when the spacer layer 3 is composed of a metal, the light detecting element 10 can embody the giant magnetoresistance (GMR) effect. This element is called a GMR element. The light detecting element 10 is sometimes called an MTJ element, a GMR element, etc., depending on the constituent material of the spacer layer 3. Although the names are different, they are also collectively referred to as magnetoresistance effect elements.

[0071] When spacer layer 3 is composed of an insulating material, materials such as aluminum oxide, magnesium oxide, titanium oxide, or silicon oxide can be used. By adjusting the thickness of spacer layer 3 to achieve a high TMR effect between first ferromagnetic layer 1 and second ferromagnetic layer 2, a high magnetoresistance change ratio can be achieved. To effectively utilize the TMR effect, the thickness of spacer layer 3 can be set to approximately 0.5 to 10.0 nm.

[0072] When the spacer layer 3 is formed of a non-magnetic conductive material, conductive materials such as Cu, Ag, Au, or Ru can be used. In order to better utilize the GMR effect, the thickness of the spacer layer 3 may be set to about 0.5 to 3.0 nm.

[0073] When the spacer layer 3 is formed of a non-magnetic semiconductor material, materials such as zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, or ITO can be used. In this case, the thickness of the spacer layer 3 can also be set to about 1.0 to 4.0 nm.

[0074] When using a layer containing energization points formed of a conductor within a non-magnetic insulator as spacer layer 3, it is preferable to adopt a structure in which energization points formed of a conductor such as CoFe, CoFeB, CoFeSi, CoMnGe, CoMnSi, CoMnAl, Fe, Co, Au, Cu, Al, or Mg are contained within a non-magnetic insulator formed of aluminum oxide or magnesium oxide. In this case, the film thickness of spacer layer 3 can be set to approximately 0.5 to 2.0 nm. The energization points are, for example, pillars with a diameter of 1 nm to 5 nm.

[0075] Figure 5The base layer 6 shown is, for example, located on the second electrode 16. The base layer 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 thickness of the seed layer is, for example, greater than 1 nm and less than 5 nm. The buffer layer is a layer that alleviates the lattice mismatch between different crystals. The buffer layer is, for example, Ta, Ti, W, Zr, Hf, or nitrides of these elements. The thickness of the buffer layer is, for example, greater than 1 nm and less than 5 nm.

[0076] 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 also include a perpendicular magnetization inducing layer 7 stacked on the first ferromagnetic layer 1 and in contact with the first ferromagnetic layer 1. The perpendicular magnetization inducing layer 7 induces perpendicular magnetic anisotropy in the first ferromagnetic layer 1. The perpendicular magnetization inducing layer 7 may be made of, for example, magnesium oxide, W, Ta, Mo, or the like. When the perpendicular magnetization inducing layer 7 is magnesium oxide, it is preferably oxygen-deficient to improve conductivity. The film thickness of the perpendicular magnetization inducing layer 7 is, for example, not less than 0.5 nm and not more than 5.0 nm. As an example, the second region 1B of the first ferromagnetic layer 1 is located between a Mo layer and an intermediate layer 1C. The Mo layer is part of the cap layer 8 and in contact with the second region 1B. In this case, the thickness of the intermediate layer 1C is preferably thinner than the thickness of the Mo layer, which is part of the cap layer 8 and in contact with the second region 1B.

[0077] The cap layer 8 prevents damage to the underlying layer during processing and improves the crystallinity of the underlying 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.

[0078] The sidewall insulating layer 9 covers the periphery of the stacked body including the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The sidewall insulating layer 9 is made of the same material as that of the interlayer insulating film 30, for example.

[0079] The first electrode 15 is, for example, transparent to light in the wavelength range used by the optical signal L1. The wavelength range used by the optical signal L1 is, for example, greater than 300 nm and less than 2 μm, including the visible light range and the near-infrared light range. The first electrode 15 is, for example, a transparent electrode such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). The first electrode 15 may also be configured to include a plurality of columnar metals within a transparent electrode material. Furthermore, the first electrode 15 may include an antireflection film on the surface irradiated with light.

[0080] The second electrode 16 is made of a conductive material and is, for example, a stacked film of Ta, Ru, and Ta, a stacked film of Ta, Cu, and Ta, a stacked film of Ta, Cu, and Ti, or a stacked film of Ta, Cu, and TaN.

[0081] The light detecting element 10 is manufactured through a process of laminating, annealing, and processing each layer. First, the base layer 6, third ferromagnetic layer 4, magnetic coupling layer 5, second ferromagnetic layer 2, spacer layer 3, first ferromagnetic layer 1, perpendicular magnetization inducing layer 7, and cap layer 8 are sequentially laminated on the second electrode 16. Each layer is deposited, for example, by sputtering.

[0082] Next, the laminated film is annealed. The annealing temperature is, for example, 250°C to 400°C. The laminated film is then processed into a predetermined columnar shape by photolithography and etching. The columnar shape can be either a cylinder or a prism. For example, the shortest width of the columnar shape when viewed in the z-direction is 10 nm to 1000 nm.

[0083] Next, an insulating layer is formed to cover the sides of the columnar body. This insulating layer becomes the sidewall insulating layer 9. Sidewall insulating layer 9 can also be laminated multiple times. Next, chemical mechanical polishing is performed to expose the upper surface of cap layer 8 from sidewall insulating layer 9, and first electrode 15 is formed on cap layer 8. Through the above steps, light detecting element 10 is obtained.

[0084] Next, an example of the operation of the light detection element 10 according to the first embodiment will be described. Light containing a light signal L1 with varying light intensity is irradiated onto the first ferromagnetic layer 1. The z-direction output voltage from the light detection element 10 changes in response to the irradiation of the first ferromagnetic layer 1 with the light containing the light signal L1. An example is given in which the intensity of the light irradiating the first ferromagnetic layer 1 is in two stages: a first intensity and a second intensity. The second intensity is set to be greater than the first intensity. Alternatively, the first intensity may be zero.

[0085] Figure 6 and Figure 7 1 is a diagram for explaining an example of the operation of the light detecting element 10 of the first embodiment. As the mechanism of the operation of the light detecting element 10, two mechanisms are considered. Figure 6 is a diagram for explaining the first mechanism, Figure 7 It is a diagram for explaining the second mechanism. Figure 6 and Figure 7 The vertical axis of the upper graph represents the intensity of light irradiating the first ferromagnetic layer 1 , and the horizontal axis represents time. Figure 6 and Figure 7 In the lower graph, the vertical axis represents the resistance value of the light detection element 10 in the z direction, and the horizontal axis represents time.

[0086] First, in a state where light of a first intensity is irradiated on the first ferromagnetic layer 1 (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 in a parallel relationship, the resistance value in the z direction of the light detection element 10 represents the first resistance value R1, and the magnitude of the output voltage from the light detection element 10 represents the first value. The resistance value in the z direction of the light detection element 10 is obtained using Ohm's law based on the voltage value generated at both ends of the light detection element 10 in the z direction by flowing the sense current Is in the z direction of the light detection element 10. The output voltage from the light detection element 10 is generated between the first electrode 15 and the second electrode 16. Figure 6 In the example shown, a sense current Is is directed from the first ferromagnetic layer 1 toward the second ferromagnetic layer 2. By directing 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, initially aligning the magnetizations M1 and M2. Furthermore, by directing the sense current Is in this direction, the magnetization M1 of the first ferromagnetic layer 1 is prevented from reversing during operation.

[0087] Next, the intensity of the light irradiating 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. The state of the magnetization M1 is, for example, the tilt angle relative to the z direction, the size, etc. For example, Figure 6 As shown in FIG. 1 , when the intensity of light irradiating the first ferromagnetic layer 1 changes from a first intensity to a second intensity, the magnetization M1 tilts relative 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 containing 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 Figure 7 As shown, when the intensity of light irradiating the first ferromagnetic layer 1 changes from a first intensity to a 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 z-direction resistance value of the light detecting element 10 indicates a second resistance value R2, and the magnitude of the output voltage from the light detecting element 10 indicates the second value. The second resistance value R2 is greater than the first resistance value R1. The second resistance value R2 lies between the resistance value when the magnetizations M1 and M2 are parallel (the first resistance value R1) and the resistance value when the magnetizations M1 and M2 are antiparallel.

[0088] The magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 act in the same direction as the spin transfer torque. Figure 6In the case shown, the magnetization M1 tilted from the initial state tries 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 light detecting element 10 returns to the initial state. Figure 7 In the case shown, when the intensity of the light irradiating the first ferromagnetic layer 1 returns to the first intensity, the magnetization M1 of the first ferromagnetic layer 1 returns to its original magnitude, and the light detecting element 10 returns to its initial state. In either case, when the magnetization M1 returns to its initial state, the z-direction resistance of the light detecting element 10 returns to the first resistance value R1. Specifically, when the intensity of the light irradiating the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the z-direction resistance of the light detecting element 10 changes from the second resistance value R2 to the first resistance value R1.

[0089] Under either mechanism, the resistance value of the light detecting element 10 in the stacking direction can change in response to changes in the intensity of light irradiating the first ferromagnetic layer 1. Changes in the intensity of the light signal L1 can be converted into changes in the z-direction resistance value of the light detecting element 10. Furthermore, the output voltage from the light detecting element 10 can change in response to changes in the intensity of light irradiating the first ferromagnetic layer 1. Changes in the intensity of the light signal L1 can be converted into changes in the output voltage from the light detecting element 10. The output from the light detecting element 10 is transmitted to the signal processing unit 11. If the output is above a threshold, it is processed as a first signal (e.g., "1"). If it is below the threshold, it is processed as a second signal (e.g., "0").

[0090] So far, an example has been given of a case where the light irradiating the first ferromagnetic layer 1 has two stages of first intensity and second intensity. The light detection element 10 of the first embodiment can also read multi-value information from the optical signal L1 by making the intensity of the light irradiating the first ferromagnetic layer 1 more than two stages.

[0091] Figure 8 and Figure 9 The behavior of the photodetection element 10 when the photodetection element 10 according to the first embodiment outputs multiple values ​​will be described. Figure 8 is a diagram for explaining the first mechanism, Figure 9 It is a diagram for explaining the second mechanism. Figure 8 and Figure 9 The magnetization state and z-direction resistance of the light detecting element 10 are shown from left to right at the first, second, third, and fourth intensities. The intensity of light irradiating the first ferromagnetic layer 1 increases in order from the fourth intensity to the third intensity, then to the second intensity, and finally to the first intensity.

[0092] like Figure 8As shown, when magnetization M1 tilts according to the intensity of irradiated light, the angular change of magnetization M1 from its initial state increases as the intensity of light irradiating the first ferromagnetic layer 1 increases. The angular change of magnetization M1 at each of the second, third, and fourth intensities relative to the orientation of magnetization M1 in the first ferromagnetic layer 1 when the first ferromagnetic layer 1 is not irradiated with light containing the optical signal L1 is greater than 0° and less than 90°. The change in the z-direction resistance of the photodetector element 10 from its initial state increases as the angular change of magnetization M1 from its initial state increases. Therefore, the z-direction resistance of the photodetector element 10 differs at each of the first, second, third, and fourth intensities. The photodetector element 10 of the first embodiment defines the output voltage threshold (resistance threshold) in multiple stages, enabling it to read out four values ​​of information: "0," "1," "2," and "3." While four values ​​are read out as an example, the number of values ​​that can be read out can be freely designed by setting the output voltage threshold (resistance threshold).

[0093] in addition, Figure 9 Similarly, when the intensity of light irradiating the first ferromagnetic layer 1 increases, the magnetization M1 of the first ferromagnetic layer 1 decreases from its initial state due to the external energy from the irradiation of light. When the magnetization M1 of the first ferromagnetic layer 1 decreases from its initial state, the resistance value in the z direction of the light detection 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 light detection element 10 changes to the second resistance value R2, the third resistance value R3, and the fourth resistance value R4. Therefore, Figure 8 Similarly to the case of , the difference in output voltage from the photodetection element 10 can be output as multi-valued or analog data.

[0094] As described above, the light detection element 10 of the first embodiment converts an optical signal into an electrical signal.

[0095] The photodetector 10 has a large magnetoresistance change rate (MR change rate) because the first region 1A in contact with the spacer layer 3 is made of CoFeB alloy. Therefore, the output of the photodetector 10 changes significantly with changes in the magnetization state of the first region 1A.

[0096] Furthermore, the photodetection element 10 includes the second region 1B which is a magnetic body containing Fe and Gd. Therefore, even when irradiated with a small amount of light, the magnetization state of the second region 1B changes, and the magnetization state of the first region 1A magnetically coupled to the second region 1B also changes.

[0097] Therefore, the output of the light detecting element 10 changes greatly with changes in the amount of irradiated light. As described above, the light detecting element 10 of the first embodiment has high efficiency in converting optical signals into electrical signals and high light detection capability.

[0098] Furthermore, in the first embodiment, the first ferromagnetic layer 1 includes the first region 1A, thereby improving the MR ratio of the light detecting element 10. Furthermore, the second ferromagnetic layer 2 includes the third region 2A, further improving the MR ratio of the light detecting element 10. While it is desirable to reduce the thickness of the first ferromagnetic layer 1 to improve the light response characteristics of the light detecting element 10, the inclusion of the first region 1A or the third region 2A in the light detecting element 10 improves the MR ratio of the light detecting element 10 even within these constraints. Consequently, the amount of change in the resistance value of the light detecting element 10 (the amount of change in the voltage output from the light detecting element 10) in response to changes in the intensity of the light signal L1 can be increased. This increases the sensitivity of the light detecting element 10, enabling its use in a receiving device 100 capable of high-speed communication.

[0099] In addition, so far, the application of the transceiver device to Figure 1 The communication system 1000 is shown as an example, but the communication system is not limited to this case.

[0100] For example, Figure 10 This is a conceptual diagram of another example of a communication system. Figure 10 The communication system 1001 shown is a communication between two mobile terminal devices 500. The mobile terminal devices 500 are, for example, smartphones, tablets, and the like.

[0101] Each mobile terminal device 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 another mobile terminal device 500. The light used for transmission and reception between the mobile terminal devices 500 is, for example, visible light. The aforementioned light detection element is employed as the light detection element 10 of each receiving device 100.

[0102] In addition, for example, Figure 11 This is a conceptual diagram of another example of a communication system. Figure 11 The communication system 1002 shown is a communication between a mobile terminal device 500 and an information processing device 600. The information processing device 600 is, for example, a personal computer.

[0103] Mobile terminal device 500 includes a transmitter 200, and information processing device 600 includes a receiver 100. An optical signal transmitted from transmitter 200 of mobile terminal device 500 is received by receiver 100 of information processing device 600. The light used for transmission and reception between mobile terminal device 500 and information processing device 600 is, for example, visible light. The aforementioned light detection elements are employed as the light detection elements 10 of each receiver 100.

[0104] As mentioned above, the present invention is not limited to the above-described embodiment and modified examples, and various modifications and changes can be made within the scope of the gist of the present invention described in the scope of the claims.

[0105] Here, the case where the light detecting element is used in the receiving device is exemplified, but the present invention is not limited to this case. For example, the light detecting element of the present invention can be substituted for various semiconductor light detecting elements such as image sensors.

[0106] Example

[0107] (Example 1)

[0108] The second electrode, the base layer, and the second ferromagnetic layer are sequentially formed on the substrate using targets of respective materials. The second electrode is sequentially formed to a thickness of 100 nm from the substrate side. Ta, thickness Ru, thickness The base layer is set to a thickness of Ta from the substrate side. Ta, thickness The second ferromagnetic layer is configured as follows: Co and thickness The Pt layer is alternately stacked 4 times; the thickness Co, thickness Ru, thickness Co, thickness Pt and thickness Co is alternately stacked three times; thickness Mo; thickness CoFeB; Fe.

[0109] Next, after forming the Mg film, an oxidation treatment is performed in an oxidation chamber to produce a thickness of Next, a Co 0.65 B 0.35 Target and Fe 0.65 B 0.35 The first region of the first ferromagnetic layer is formed by co-sputtering (two-dimensional simultaneous sputtering) of the target material. Next, as an intermediate layer, a film with a thickness of Next, co-sputtering (two-dimensional simultaneous sputtering) using a Gd target and an Fe target is performed on the intermediate layer to deposit the second region of the first ferromagnetic layer with The thickness of the film is formed.

[0110] Then, a cap layer is formed on the first ferromagnetic layer. The cap layer is formed to a thickness of Mo, thickness Ta, thickness Thereafter, annealing treatment was performed in vacuum at 400°C for 30 minutes. Then, a first electrode was formed on the annealed laminate and processed into a cylindrical shape with a diameter of 300 nm to produce a light detection element. The first electrode was set to a thickness of The film formation of each layer is carried out by a DC magnetron sputtering device.

[0111] The element structure of the light detection element produced in Example 1 is summarized below.

[0112] Second electrode:

[0113] Basal layer:

[0114] Second ferromagnetic layer:

[0115] Spacer layer:

[0116] First ferromagnetic layer:

[0117] Covering layer:

[0118] First electrode:

[0119] The manufactured light detection element is irradiated with pulse light from the first electrode side. A 50mW short pulse laser (wavelength 800nm) is used as the light source. The light pulse width is set to 50fsec, the light spot diameter is set to 2mm, and the intensity of the 50mW pulse light is reduced to 1 / 1000 before irradiating the light detection element. A DC current of 0.25mA is applied to the light detection element. Then, the change in the output voltage from the light detection element caused by irradiating the light detection element with pulse light is measured by a high-speed oscilloscope. For the light detection element of Example 1, the change in the output voltage before and after irradiation with pulse light is 5.0mV.

[0120] (Example 2)

[0121] In Example 2, the structure of the second region of the first ferromagnetic layer is changed from that of Example 1. In Example 2, co-sputtering (three-dimensional simultaneous sputtering) using a Gd target, an Fe target, and a Co target is performed on the intermediate layer to form the second region of the first ferromagnetic layer. The film is formed into a thickness of .

[0122] 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.

[0123] First ferromagnetic layer:

[0124] In Example 2, pulse light was irradiated in the same manner as in Example 1, and the change in output voltage before and after irradiation was measured. The change in output voltage before and after irradiation of the light detection element in Example 2 was 4.8 mV.

[0125] (Example 3)

[0126] Example 3 is different from Example 1 in that the structure of the second region of the first ferromagnetic layer is changed. In Example 3, the thickness of the intermediate layer is increased. Fe, and thickness Gd is alternately stacked five times to form the second region of the first ferromagnetic layer.

[0127] 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.

[0128] First ferromagnetic layer:

[0129] In Example 3, pulse light was irradiated in the same manner as in Example 1, and the change in output voltage before and after irradiation was measured. In the light detection element of Example 3, the change in output voltage before and after irradiation with pulse light was 9.8 mV.

[0130] (Example 4)

[0131] Example 4 is different from Example 1 in that the structure of the second region of the first ferromagnetic layer is changed. In Example 4, the thickness of the intermediate layer is increased. FeCo alloy film and thickness The FeCo alloy film was formed by co-sputtering (two-dimensional simultaneous sputtering) using an Fe target and a Co target.

[0132] 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.

[0133] First ferromagnetic layer:

[0134] In Example 4, pulse light was irradiated in the same manner as in Example 1, and the change in output voltage before and after irradiation was measured. In the light detection element of Example 4, the change in output voltage before and after irradiation with pulse light was 10.0 mV.

[0135] (Comparative Example 1)

[0136] Comparative Example 1 differs from Example 1 in that the structure of the first ferromagnetic layer is changed. In Comparative Example 1, unlike Example 1, the intermediate layer and the second region of the first ferromagnetic layer 1 are not formed.

[0137] The layer structure of the first ferromagnetic layer in Comparative Example 1 is as follows, and the structures of the other layers are the same as those in Example 1.

[0138] First ferromagnetic layer:

[0139] In Comparative Example 1, pulse 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 irradiation of the light detection element in Comparative Example 1 was 2.5 mV.

[0140] The results of Examples 1 to 4 and Comparative Example 1 are summarized in the following table. As shown in Table 1, the photodetection elements of Examples 1 to 4 have higher efficiency in converting optical signals into electrical signals than the photodetection element of Comparative Example 1.

[0141]

Table 1

[0142] Output voltage change before and after pulse light irradiation (mV) Example 1 5.0 Example 2 4.8 Example 3 9.8 Example 4 10.0 Comparative Example 1 2.5

Claims

1. A light detecting element, wherein: The invention comprises: a first ferromagnetic layer 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 includes 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 body mainly containing Fe and Gd as constituent elements. The total molar fraction of Fe and Gd in the constituent elements of the second region is 70% or more.

2. The light detecting element according to claim 1, wherein The second region is a laminated film in which Fe and Gd are laminated, or a laminated film in which an FeCo alloy and Gd are laminated.

3. The light detecting element according to claim 1, wherein There is also an intermediate layer between the first region and the second region, The intermediate layer contains at least one element selected from the group consisting of Mo, Ru, Ta, W, and Pt.

4. The light detecting element according to claim 2, wherein There is also an intermediate layer between the first region and the second region, The intermediate layer contains at least one element selected from the group consisting of Mo, Ru, Ta, W, and Pt.

5. The light detecting element according to any one of claims 1 to 4, wherein The second ferromagnetic layer includes a third region in contact with the spacer layer and a fourth region located farther from the spacer layer than the third region and containing boron. Compared with the fourth region, the third region has a lower boron concentration or contains no boron.

6. The light detection element according to any one of claims 1 to 4, wherein The first region has a higher boron concentration than the second region.

7. The light detecting element according to claim 5, wherein The first region has a higher boron concentration than the second region.

8. The light detecting element according to claim 5, wherein The third region contains Fe or CoFe alloy, and has a bcc crystal structure.

9. A receiving device, wherein: A light detecting element according to any one of claims 1 to 8.

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