JP2022070205A - Light detection element and receiving device - Google Patents

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

The present invention relates to a photodetector and a receiver.

With the spread of the Internet, the amount of communication has increased dramatically, and the importance of optical communication has become extremely high. Optical communication is a communication means that converts an electric signal into an optical signal and transmits / receives using the optical signal.

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 pn junction of a semiconductor. Further, for example, Patent Document 2 describes an optical sensor using a pn junction of a semiconductor and an image sensor using this optical sensor.

Japanese Unexamined Patent Publication No. 2001-292107 US Pat. No. 9,842,874

A photodetector using a pn junction of a semiconductor is widely used, but a new photodetector is required for further development. Further, the photodetector element converts light into an electric signal, and is required to have a high efficiency of converting light into an electric signal and a high photodetection ability.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a photodetector element having a high photodetection ability.

The following means are provided to solve the above problems.

(1) The light detection element according to the first aspect is sandwiched between a first ferromagnetic layer to which light is irradiated, a second ferromagnetic layer, and 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 away from the spacer layer from the first region. One region is a CoFeB alloy, and the second region is a magnetic material mainly containing Fe and Gd as constituent elements.

(2) The photodetector according to the above aspect further has an intermediate layer between the first region and the second region, and the intermediate layer is composed of a group consisting of Mo, Ru, Ta, W, and Pt. It may contain any one or more selected elements.

(3) In the photodetecting 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 at a position distant from the spacer layer from the third region. The third region may have a lower concentration of boron than the fourth region, or may not contain boron.

(4) In the photodetector according to the above aspect, the concentration of boron in the first region may be higher than that in the second region.

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

(6) The receiving device according to the second aspect has the photodetector element according to the above aspect.

The photodetector element according to the above aspect has a high photodetection ability.

It is a conceptual diagram of the communication system which concerns on 1st Embodiment. It is a block diagram of the transmission / reception device which concerns on 1st Embodiment. It is a circuit diagram of the transmission / reception device which concerns on 1st Embodiment. It is sectional drawing of the receiving apparatus which concerns on 1st Embodiment. It is sectional drawing of the light detection element which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the 1st mechanism of operation of the photodetector element which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the 2nd mechanism of operation of the photodetector element which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the 1st mechanism of the operation of the photodetector element at the time of outputting a multi-value by using the photodetector element which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the 2nd mechanism of operation of the photodetector element at the time of outputting a multi-value by using the photodetector element which concerns on 1st Embodiment. It is a conceptual diagram of another example of a communication system. It is a conceptual diagram of another example of a communication system.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, the featured portion may be enlarged for convenience in order to make the feature easy to understand, and the dimensional ratio of each component may be different from the actual one. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited thereto, and can be appropriately modified and carried out within the range in which the effects of the present invention are exhibited.

Define the direction. The stacking direction of the light detection elements 10 is the z direction, one direction in the plane orthogonal to the z direction is the x direction, and the x direction and the direction orthogonal to the z direction are the y direction. The z direction is an example of the stacking direction. Hereinafter, the + z direction may be expressed as “up” and the −z direction may be expressed as “down”. The + z direction is the direction from the substrate Sb toward the photodetector element 10. The top and bottom do not always match the direction in which gravity is applied.

"First embodiment"
FIG. 1 is a conceptual diagram of the 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. The communication system 1000 can be used, for example, for short- and medium-distance communication such as within and between data centers, and long-distance communication such as between cities. The transmission / reception device 300 is installed in, for example, a data center. The fiber FB connects, for example, between data centers. The communication system 1000 communicates between the transmission / reception device 300 via, for example, the fiber FB. The communication system 1000 may wirelessly communicate between the transmission / reception devices 300 without going through the fiber FB.

FIG. 2 is a block diagram of the 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 receiving device 100 receives the optical signal L1, and the transmitting device 200 transmits the optical signal L2. The light in the present specification is not limited to visible light, but also includes infrared rays having a wavelength longer than that of visible light and ultraviolet rays having a wavelength shorter than that of visible light.

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

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

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

The receiving device 100 includes, for example, a photodetector 10, a first electrode 15, a second electrode 16, an input terminal P _in , an output terminal P _out , and a 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, an electrode on the side to be irradiated with light including an optical signal L1. The wavelength of the light used for the optical signal L1 is, for example, 300 nm or more and 2 μm or less, and the light used for the optical signal L1 may be visible light or near-infrared light.

The first electrode 15 is connected to, for example, an input terminal P _in and an output terminal P _out . The second electrode 16 is connected to, for example, the reference potential terminal _PG . The input terminal _Pin is connected to the power supply PS. The power supply PS may be outside the receiving device 100. The power supply PS applies a sense current or the like to the photodetector element 10. When it is not necessary to pass an external current through the photodetector 10, the input terminal _Pin and the power supply PS may be omitted. The output terminal P _out outputs a voltage between the first electrode 15 and the second electrode 16 that sandwich the photodetector element 10 in the stacking direction. The resistance value in the stacking direction of the photodetector 10 is obtained from Ohm's law by passing a sense current in the stacking direction of the photodetector 10. The output terminal P _out is connected to the signal processing unit 11. The reference potential terminal _PG is connected to the reference potential and determines the reference potential of the receiving device 100. The reference potential in FIG. 3 is ground G. The ground G may be provided outside the receiving device 100. The reference potential may be other than ground G.

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

FIG. 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 10, an integrated circuit 20, and an interlayer insulating film 30. The photodetector 10, the integrated circuit 20, and the interlayer insulating film 30 are formed on, for example, the same substrate Sb.

The integrated circuit 20 includes a signal processing unit 11 that processes a signal output from the photodetector element 10. In the integrated circuit 20, for example, 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 equal to or more than the threshold value is regarded as the first signal (for example, “1”), and the case where the output voltage is less than the threshold value is defined as the first signal. It is processed as a second signal (for example, “0”). When the transmission device 200 is formed on the same substrate Sb, the integrated circuit 20 may include a light source 201, an electric signal generation element 202, and a light modulation element 203. The integrated circuit 20 and the photodetector 10 are connected, for example, via a through wiring w penetrating the interlayer insulating film 30. These may be connected by wire bonding instead of the through wiring w.

The interlayer insulating film 30 is an insulator that insulates between wirings of multilayer wiring and between elements. The interlayer insulating film 30 is, for example, an oxide of Si, Al, or Mg, a nitride, or an oxynitride. The interlayer insulating film 30 is, for example, silicon oxide (SiO _x ), silicon nitride (SiN _x ), silicon carbide (SiC), chromium nitride, silicon carbide (SiCN), silicon oxynitride (SiON), aluminum oxide (Al ₂ ). O ₃ ), zirconium oxide (ZrO _x ) and the like.

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 shown at the same time, and the direction of magnetization in the initial state of the ferromagnet is indicated by an arrow. As used herein, ferromagnetism includes ferrimagnetism.

The photodetection 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 photodetection element 10 may 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 side wall insulating layer 9.

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. Is. In this case, the light detection element 10 has a resistance value in the z direction (current in the z direction) 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. It is an element whose resistance value) changes. Such an element is also called a magnetoresistive effect element.

The first ferromagnetic layer 1 is a photodetection 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 material whose magnetization direction changes when a predetermined external force is applied. The predetermined external force is, for example, light emitted from the outside, a current flowing in the z direction of the photodetector element 10, and an external magnetic field. Since the magnetization of the ferromagnetic material can change its direction following a high-speed change in the intensity of light (high-frequency optical signal) applied to the ferromagnetic material, the first ferromagnetic layer 1 is used as the light detection layer. By using this, the receiving device 100 can receive a high-frequency optical signal, and high-speed optical communication becomes possible.

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 away from the spacer layer 3 from the first region 1A. The intermediate layer 1C is between the first region 1A and the second region 1B. Each of the first region 1A and the second region 1B spreads in layers in, for example, the x direction and the y direction.

The first region 1A contains a ferromagnet. The first region 1A may have a higher concentration of boron 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 rate of change in magnetic resistance (rate of change in MR) of the photodetector element 10 becomes large. 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 becomes large with respect to the change in the magnetization state of the first region 1A. The composition ratio of the CoFeB alloy can be changed as appropriate. The elemental ratio of the CoFeB alloy is, for example, Co: Fe: B = 15 to 55:25 to 65: 15 to 25 under the condition that the sum of Co, Fe, and B is 100.

The film thickness of the first region 1A is, for example, 5 Å or more and 20 Å or less, preferably 8 Å or more and 15 Å or less, and more preferably 10 Å or less. Hereinafter, the film thickness of each layer and the film thickness of each region are taken as the average value of the thicknesses in the z direction at 10 different points in the xy plane.

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

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 a FeCo alloy and Gd are laminated. For example, as an example of a GdFe alloy or a GdFeCo alloy, there is Gd _x (Fe _{1-y Coy} ) _1-x . Here, 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. Further, for example, as an example of the laminated film, there is [Fe _{1-y Coy} / Gd] _z . Here, y is, for example, 0 or more and 0.2 or less, and z is the number of layers, for example, 4 or more and 10 or less. The thickness of each Fe _{1-y Coy} 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 stack of a plurality of layers made of a single element. In the second region 1B, the total molar fraction of Fe and Gd among the constituent elements is, for example, 70% or more.

The second region 1B is, for example, a perpendicular magnetization film having an easy magnetization axis in the direct direction (z direction) of the film surface. 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.

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

The intermediate layer 1C contains any 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 composed 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 interposed therebetween. The film thickness of the intermediate layer 1C is, for example, 10 Å or less. The film thickness of the intermediate layer 1C is, for example, 1 Å or more and 10 Å or less.

The total film thickness of the first ferromagnetic layer 1 is, for example, 1 nm or more and 10 nm or less. The film thickness of the first ferromagnetic layer 1 is preferably 1 nm or more and 5 nm or less, for example. When the film thickness of the first ferromagnetic layer 1 is thin, the vertical magnetic anisotropy of the first ferromagnetic layer 1 increases. By providing the first region 1A in the first ferromagnetic layer 1, the MR ratio of the light detection element 10 is improved even when the first ferromagnetic layer 1 is thin, and the change in the magnetization state of the first ferromagnetic layer 1 The ratio of the output change of the light detection element 10 to the light detection element 10 is improved.

When the first ferromagnetic layer 1 has the intermediate layer 1C, the influence of the difference in the crystal structure between the first region 1A and the second region 1B can be mitigated. By reducing the difference in crystal structure between the first region 1A and the second region 1B by the intermediate layer 1C, the crystallinity of the second region 1B formed on the intermediate layer 1C is improved.

In the second region 1B, it is considered that the magnetic moment of the Fe atom and the magnetic moment of the Gd atom are ferrimagnetically bonded. The magnetic moment of the Gd atom tends to change its state with respect to the irradiation of light. Therefore, the magnetization of the second region 1B is more likely to change with light irradiation as compared with the magnetization of the first region 1A in the case where the second region 1B does not exist in the first ferromagnetic layer 1. .. When the magnetization state of the second region 1B changes, the magnetization state of the first region 1A that magnetically couples with the second region 1B across the intermediate layer 1C also changes.

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 than the magnetization free layer when a predetermined external force is applied. The coercive force of the second ferromagnetic layer 2 is, for example, larger than the coercive force of the first ferromagnetic layer 1. The second ferromagnetic layer 2 has an easy magnetization axis in the same direction as the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be an in-plane magnetizing film or a perpendicular magnetization film.

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 away from the spacer layer 3 from the third region 2A. Each of the third region 2A and the fourth region 2B spreads in layers in, for example, the x direction and the y direction.

The third region 2A contains a ferromagnet. The third region 2A may contain no boron or may have a lower boron concentration than the fourth region 2B, for example. The third region 2A contains, for example, an Fe or CoFe alloy. The third region 2A may be made of Fe or 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 has the third region 2A, the MR ratio of the photodetector 10 is improved.

The fourth region 2B contains a ferromagnet. The fourth region 2B may be a single alloy or may be a stack of a plurality of 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 contains, for example, a CoFeB alloy. The fourth region 2B may have a non-magnetic insertion layer made of, for example, W and Ta inside. The fourth region 2B may have, for example, a Co or CoFe alloy, a laminated film of Co and Pt, an insertion layer composed of Mo and Ta, and a CoFeB alloy in order from the side far from the spacer layer 3. The film thickness of the fourth region 2B is, for example, 30 Å or more and 100 Å or less, preferably 50 Å or more and 70 Å or less.

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.

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

The spacer layer 3 is a non-magnetic layer arranged 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 an energizing point made of a conductor in the insulator. The film thickness of the spacer layer 3 can be adjusted according to the orientation direction of the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 in the initial state described later.

For example, when the spacer layer 3 is made of an insulator, the light detection element 10 has a magnetic tunnel junction (MTJ: Magnetic Tunnel Junction) including a first ferromagnetic layer 1, a spacer layer 3, and a second ferromagnetic layer. .. Such an element is called an MTJ element. In this case, the photodetector element 10 can exhibit a tunnel magnetoresistive (TMR) effect. For example, when the spacer layer 3 is made of metal, the photodetector element 10 can exhibit a giant magnetoresistive (GMR) effect. Such an element is called a GMR element. The photodetection element 10 may be referred to as an MTJ element, a GMR element, or the like depending on the constituent material of the spacer layer 3, but is also collectively referred to as a magnetoresistive effect element.

When the spacer layer 3 is made of an insulating material, a material such as aluminum oxide, magnesium oxide, titanium oxide or silicon oxide can be used. A high rate of change in magnetic resistance can be obtained by adjusting the film 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. In order to efficiently utilize the TMR effect, the film thickness of the spacer layer 3 may be about 0.5 to 10.0 nm.

When the spacer layer 3 is made of a non-magnetic conductive material, a conductive material such as Cu, Ag, Au or Ru can be used. In order to efficiently utilize the GMR effect, the film thickness of the spacer layer 3 may be about 0.5 to 3.0 nm.

When the spacer layer 3 is made of a non-magnetic semiconductor material, a material such as zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide or ITO can be used. In this case, the film thickness of the spacer layer 3 may be about 1.0 to 4.0 nm.

When a layer including a current-carrying point composed of a conductor in a non-magnetic insulator is applied as the spacer layer 3, CoFe, CoFeB, CoFeSi, CoMnGe, and CoMnSi are contained in the non-magnetic insulator composed of aluminum oxide or magnesium oxide. , ComnAl, Fe, Co, Au, Cu, Al or Mg, it is preferable to have a structure including a current-carrying point composed of a conductor. In this case, the film thickness of the spacer layer 3 may be about 0.5 to 2.0 nm. The energizing point is, for example, a columnar body having a diameter of 1 nm or more and 5 nm or less.

The base layer 6 shown in FIG. 5 is, for example, on the second electrode 16. The base layer 6 is a seed layer or a buffer layer. The seed layer enhances the crystallinity of the layer laminated on the seed layer. The seed layer is, for example, Pt, Ru, Hf, Zr, NiFeCr. The film thickness of the seed layer is, 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 a nitride of these elements. The film thickness of the buffer layer is, for example, 1 nm or more and 5 nm or less.

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 induced layer 7 laminated on the first ferromagnetic layer 1 and in contact with the first ferromagnetic layer 1. The perpendicular magnetization-inducing layer 7 induces the perpendicular magnetic anisotropy of the first ferromagnetic layer 1. The perpendicular magnetization induced layer 7 is, for example, magnesium oxide, W, Ta, Mo or the like. When the perpendicular magnetization induced layer 7 is magnesium oxide, it is preferable that magnesium oxide is oxygen-deficient in order to enhance conductivity. The film thickness of the perpendicular magnetization induced layer 7 is, for example, 0.5 nm or more and 5.0 nm or less. As an example, the second region 1B of the first ferromagnetic layer 1 is between the Mo layer and the intermediate layer 1C. The Mo layer is a part of the cap layer 8 and is 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 a part of the cap layer 8 and is in contact with the second region 1B.

The cap layer 8 prevents damage to the lower layer during the process and enhances the crystallinity of the lower layer at the time of annealing. The film 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.

The side wall insulating layer 9 covers the periphery of the laminate including the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The side wall insulating layer 9 is made of, for example, the same material as the interlayer insulating film 30.

The first electrode 15 has, for example, transparency with respect to light in the wavelength range used for the optical signal L1. The wavelength range of the light used for the optical signal L1 is, for example, 300 nm or more and 2 μm or less, and includes a visible light range and a near infrared light range. The first electrode 15 is a transparent electrode such as indium tin oxide (ITO), zinc oxide (IZO), zinc oxide (ZnO), and indium gallium oxide zinc (IGZO). The first electrode 15 may be configured to have a plurality of columnar metals in the transparent electrode material. Further, the first electrode 15 may have an antireflection film on the irradiation surface irradiated with light.

The second electrode 16 is made of a conductive material. The second electrode 16 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, and a laminated film of Ta, Cu and TaN.

The photodetector element 10 is manufactured by a laminating step, an annealing step, and a processing step of each layer. First, on the second electrode 16, the base layer 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 vertical magnetization induced layer 7, and the cap. Layers 8 are laminated in this order. Each layer is formed by, for example, sputtering.

Then, the laminated film is annealed. The annealing temperature is, for example, 250 ° C. or higher and 400 ° C. or lower. After that, the laminated film is processed into a predetermined columnar body by photolithography and etching. The columnar body may be a cylinder or a prism. For example, the shortest width when the columnar body is viewed from the z direction is 10 nm or more and 1000 nm or less.

Next, an insulating layer is formed so as to cover the side surface of the columnar body. The insulating layer is the side wall insulating layer 9. The side wall insulating layer 9 may be laminated a plurality of times. Next, the upper surface of the cap layer 8 is exposed from the side wall insulating layer 9 by chemical mechanical polishing, and the first electrode 15 is manufactured on the cap layer 8. By the above steps, the photodetector element 10 is obtained.

Next, an example of the operation of the photodetector element 10 according to the first embodiment will be described. The first ferromagnetic layer 1 is irradiated with light including an optical signal L1 having a change in light intensity. The output voltage of the photodetector 10 from the z direction changes due to irradiation of the first ferromagnetic layer 1 with light including the optical signal L1. A case where the intensity of the light applied to the first ferromagnetic layer 1 has two stages of the first intensity and the second intensity will be described as an example. The intensity of the light of the second intensity shall be larger than the intensity of the light of the first intensity. The first intensity may be a case where the intensity of the light applied to the first ferromagnetic layer 1 is zero.

6 and 7 are diagrams for explaining an example of the operation of the photodetector element 10 according to the first embodiment. Two mechanisms are considered as the mechanism of operation of the photodetector 10, FIG. 6 is a diagram for explaining the first mechanism, and FIG. 7 is a diagram for explaining the second mechanism. In the upper graphs of FIGS. 6 and 7, the vertical axis is the intensity of light irradiating the first ferromagnetic layer 1, and the horizontal axis is time. In the graphs in the lower part of FIGS. 6 and 7, the vertical axis is the resistance value of the photodetector 10 in the z direction, and the horizontal axis is time.

First, in a state where the first ferromagnetic layer 1 is irradiated with light of the first intensity (hereinafter referred to as an initial state), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are parallel to each other. The resistance value of the light detection element 10 in the z direction indicates the first resistance value R ₁ , and the magnitude of the output voltage from the light detection element 10 indicates the first value. The resistance value of the photodetector 10 in the z direction is such that a voltage is generated at both ends of the photodetector 10 in the z direction by passing a sense current Is in the z direction of the photodetector 10, and Ohm's law is derived from the voltage value. Is obtained using. The output voltage from the photodetector 10 is generated between the first electrode 15 and the second electrode 16. In the case of the example shown in FIG. 6, the sense current Is is passed from the first ferromagnetic layer 1 to the second ferromagnetic layer 2. By passing the sense current Is in this direction, the spin transfer torque in the same direction as the magnetization M2 of the second ferromagnetic layer 2 acts on the magnetization M1 of the first ferromagnetic layer 1, and in the initial state, the magnetization M1 and It becomes parallel to the magnetization M2. Further, by passing the sense current Is in this direction, it is possible to prevent the magnetization M1 of the first ferromagnetic layer 1 from being inverted during operation.

Next, the intensity of the light applied to the first ferromagnetic layer 1 changes from the first intensity to the second intensity. The second intensity is larger 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, a tilt angle, a magnitude, or the like with respect to the z direction. For example, as shown in FIG. 6, when the intensity of the light applied to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnetization M1 is tilted in the z direction. The angle between the direction of the magnetization M1 of the first ferromagnetic layer 1 in the state where the first ferromagnetic layer 1 is not irradiated with the 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 °. Further, for example, as shown in FIG. 7, when the intensity of the light applied to the first ferromagnetic layer 1 changes from the first intensity to the second intensity, the magnitude of the magnetization M1 becomes smaller. When the magnetization M1 of the first ferromagnetic layer 1 changes from the initial state, the resistance value in the z direction of the photodetector 10 shows the _second resistance value R2, and the magnitude of the output voltage from the photodetector 10 is the second. Indicates the value of. The second resistance value R ₂ is larger than the first resistance value R ₁ . The second resistance value R ₂ is between the resistance value when the magnetization M1 and the magnetization M2 are parallel (the first resistance value R ₁ ) and the resistance value when the magnetization M1 and the magnetization M2 are antiparallel. Is.

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. Therefore, in the case shown in FIG. 6, the magnetization M1 tilted from the initial state tries to return to the state parallel to the magnetization M2, and the intensity of the light applied to the first ferromagnetic layer 1 changes from the second intensity to the first intensity. , The light detection element 10 returns to the initial state. In the case shown in FIG. 7, when the intensity of the light applied to the first ferromagnetic layer 1 returns to the first intensity, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 returns to the original size, and the light detection element 10 is used. Return to the initial state. In either case, when the magnetization M1 returns to the initial state, the resistance value of the photodetector 10 in the z direction returns to the _first resistance value R1. That is, when the intensity of the light applied to the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the resistance value of the light detection element 10 in the z direction changes from the second resistance value _R2 to the first. The resistance value changes to _R1 .

In either mechanism, the resistance value in the stacking direction of the photodetector 10 changes in response to the change in the intensity of the light applied to the first ferromagnetic layer 1, and the change in the intensity of the optical signal L1 is detected. It can be converted into a change in the resistance value of the element 10 in the z direction. Further, the output voltage from the photodetector 10 changes in response to the change in the intensity of the light applied to the first ferromagnetic layer 1, and the change in the intensity of the optical signal L1 is the output voltage from the photodetector 10. Can be transformed into change. The output from the photodetector 10 is sent to the signal processing unit 11, and if the output is equal to or greater than the threshold value, the first signal (for example, “1”) is sent, and if the output is less than the threshold value, the second signal (for example, “0”). Is processed as.

Up to this point, the case where the light irradiated to the first ferromagnetic layer 1 has two stages of the first intensity and the second intensity has been described as an example, but the light detection element 10 according to the first embodiment is the first. By increasing the intensity of the light applied to the ferromagnetic layer 1 to more than two steps, it is possible to read out multi-valued information from the optical signal L1.

8 and 9 show the behavior of the photodetector 10 when the photodetector 10 according to the first embodiment is used to output multiple values. FIG. 8 is a diagram for explaining the first mechanism, and FIG. 9 is a diagram for explaining the second mechanism. 8 and 9 show the magnetization state of the photodetector 10 and the resistance value in the z direction at each of the first intensity, the second intensity, the third intensity, and the fourth intensity in order from the left. The intensity of the light applied to the first ferromagnetic layer 1 is stronger in the order of the fourth intensity, the third intensity, the second intensity, and the first intensity.

As shown in FIG. 8, when the magnetization M1 is tilted according to the intensity of the irradiated light, the angle change from the initial state of the magnetization M1 increases as the intensity of the light irradiated to the first ferromagnetic layer 1 increases. Become. The angular changes of the second intensity, the third intensity, and the fourth intensity with respect to the direction of the magnetization M1 of the first ferromagnetic layer 1 in the state where the first ferromagnetic layer 1 is not irradiated with the light including the optical signal L1 are , Both are greater than 0 ° and less than 90 °. The change in the resistance value of the photodetector 10 in the z direction with respect to the initial state becomes larger as the angle change from the initial state of the magnetization M1 becomes larger. Therefore, the resistance value of the photodetector 10 in the z direction differs depending on each of the first intensity, the second intensity, the third intensity, and the fourth intensity. The photodetector 10 according to the first embodiment defines, for example, "0", "1", "2", "3" by defining the threshold value of the output voltage (threshold value of the resistance value) in a plurality of stages. The four-valued information of "" can be read out. Here, the case of reading out four values is shown as an example, 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 value).

Similarly, in the case of FIG. 9, when the intensity of the light irradiated to the first ferromagnetic layer 1 increases, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 becomes the initial state due to the external energy generated by the irradiation of the light. Becomes smaller from. When the magnetization M1 of the first ferromagnetic layer 1 becomes smaller than the initial state, the resistance value of the photodetector 10 in the z direction changes. For example, depending on the magnitude of the magnetization M1 of the first ferromagnetic layer 1, the resistance values of the light detection element 10 in the z direction are the second resistance value R ₂ , the third resistance value R ₃ , and the fourth resistance value R ₄ . It changes with. Therefore, as in the case of FIG. 8, the difference in the output voltage from the photodetector element 10 can be output as multi-valued or analog data.

As described above, the photodetector element 10 according to the first embodiment converts an optical signal into an electric signal.

In the photodetector element 10, since the first region 1A in contact with the spacer layer 3 is a CoFeB alloy, the rate of change in magnetic resistance (rate of change in MR) is large. Therefore, in the photodetector element 10, the output change of the photodetector element 10 is large with respect to the change in the magnetization state of the first region 1A.

Further, since the photodetector 10 has a second region 1B which is a magnetic material containing Fe and Gd, the state of magnetization of the second region 1B changes even when irradiated with a small amount of light, and magnetically couples with the second region 1B. The state of magnetization of the first region 1A also changes.

Therefore, the output of the photodetector element 10 changes greatly with respect to the change in the amount of emitted light. As described above, the photodetector element 10 according to the first embodiment has a high conversion efficiency of an optical signal into an electric signal and a high photodetection ability.

Further, in the first embodiment, the MR ratio of the photodetector element 10 is improved by having the first ferromagnetic layer 1 having the first region 1A. Further, when the second ferromagnetic layer 2 has the third region 2A, the MR ratio of the photodetector 10 is improved. There is a desire to reduce the thickness of the first ferromagnetic layer 1 in order to enhance the response characteristics of the photodetector element 10 to light, but the photodetector element 10 has a first region 1A and a third region 2A. Even within these restrictions, the MR ratio of the photodetector 10 can be increased. As a result, the amount of change in the resistance value of the photodetector element 10 (the amount of change in the voltage output from the photodetector element 10) with respect to the change in the light intensity of the optical signal L1 can be increased. As a result, the sensitivity of the photodetector element 10 can be increased, and the photodetector element 10 can be used for the receiving device 100 that enables high-speed communication.

Further, although an example of applying the transmission / reception device to the communication system 1000 shown in FIG. 1 has been shown so far, the communication system is not limited to this case.

For example, FIG. 10 is a conceptual diagram of another example of a communication system. The communication system 1001 shown in FIG. 10 is a communication between two mobile terminal devices 500. The mobile terminal device 500 is, for example, a smartphone, a tablet, or the like.

Each of the mobile terminal devices 500 includes a receiving device 100 and a transmitting device 200. The 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 / reception between the mobile terminal devices 500 is, for example, visible light. The above-mentioned photodetector is applied as the photodetector 10 of each receiver 100.

Also, for example, FIG. 11 is a conceptual diagram of another example of a communication system. The communication system 1002 shown in FIG. 11 is communication between the mobile terminal device 500 and the information processing device 600. The information processing device 600 is, for example, a personal computer.

The mobile terminal device 500 includes a transmitting device 200, and the information processing device 600 includes a receiving device 100. The 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 / reception between the mobile terminal device 500 and the information processing device 600 is, for example, visible light. The above-mentioned photodetector is applied as the photodetector 10 of each receiver 100.

As described above, the present invention is not limited to the above-described embodiments and modifications, and various modifications and modifications can be made within the scope of the gist of the present invention described within the scope of claims.

Here, the case where the photodetector is used for the receiving device is illustrated, but the case is not limited to this case. For example, the photodetector according to the present invention can be replaced with various semiconductor photodetectors such as image sensors.

(Example 1)
A second electrode, a base layer, and a second ferromagnetic layer were formed on the substrate in this order using targets of each material. The second electrode was Ta with a thickness of 50 Å, Ru with a thickness of 600 Å, and Ta with a thickness of 100 Å in order from the substrate side. The base layer was Ta with a thickness of 20 Å and Pt with a thickness of 20 Å in order from the substrate side. The second ferromagnetic layer is a laminated film in which Co with a thickness of 5 Å and Pt with a thickness of 4 Å are alternately laminated four times in order from the substrate side, Co with a thickness of 6 Å, Ru with a thickness of 8 Å, and 6 Å with a thickness. Co, Pt having a thickness of 4 Å and Co having a thickness of 5 Å were alternately laminated three times to form a laminated film, Mo having a thickness of 4 Å, CoFeB having a thickness of 6 Å, and Fe having a thickness of 5 Å.

Next, after forming Mg into a film, an oxidation treatment was performed in an oxidation chamber to prepare a spacer layer of MgO having a thickness of 12 Å. Next, co-sputtering (binary simultaneous sputtering) using a target of Co _0.65 B _0.35 and a target of Fe _0.65 B _0.35 was performed on the spacer layer, and the first ferromagnetic layer was first. One region was formed with a thickness of 10 Å. Next, Mo having a thickness of 5 Å was formed as an intermediate layer. Then, co-sputtering (binary simultaneous sputtering) using a Gd target and a Fe target was performed on the intermediate layer to form a second region of the first ferromagnetic layer with a thickness of 25 Å.

Then, a cap layer was formed on the first ferromagnetic layer. The cap layer was Mo having a thickness of 20 Å, Ta having a thickness of 20 Å, and Ru having a thickness of 20 Å in order from the substrate side. Then, it was annealed at 400 ° C. for 30 minutes in vacuum. Then, a first electrode was formed on the laminated body after the annealing treatment, and processed into a columnar shape having a diameter of 300 nm to produce a photodetector. The first electrode was indium tin oxide (ITO) having a thickness of 500 Å. The film formation of each layer was performed by a DC magnetron sputtering apparatus.

The element configuration of the photodetector element produced in Example 1 is summarized below.
Second electrode: Ta (50 Å) / Ru (600 Å) / Ta (100 Å)
Underlayer: Ta (20 Å) / Pt (20 Å)
Second ferromagnetic layer: [Co (5 Å) / Pt (4 Å)] ₄ / Co (6 Å) / Ru (8 Å) / Co (6 Å) / [Pt (4 Å) / Co (5 Å)] ₃ / Mo (4 Å) ) / CoFeB (6 Å) / Fe (5 Å)
Spacer layer: MgO (12Å)
First ferromagnetic layer: Co _0.24 Fe _0.56 B _0.20 (10 Å) / Mo (5 Å) / Gd _0.26 Fe _0.74 (25 Å)
Cap layer: Mo (20 Å) / Ta (20 Å) / Ru (20 Å)
First electrode: ITO (500 Å)

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

(Example 2)
Example 2 is different from Example 1 in that the configuration of the second region of the first ferromagnetic layer is changed. In Example 2, co-sputtering (ternary simultaneous sputtering) using a Gd target, an Fe target, and a Co target is performed on the intermediate layer, and the second region of the first ferromagnetic layer is formed with a thickness of 25 Å. Membrane.

The layer structure of the first ferromagnetic layer in Example 2 is as follows, and the structure of the other layers is the same as that in Example 1.
First ferromagnetic layer: Co _0.24 Fe _0.56 B _0.20 (10 Å) / Mo (5 Å) / Gd _0.26 (Fe _0.90 Co _0.10 ) _0.74 (25 Å)

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

(Example 3)
Example 3 is different from Example 1 in that the configuration of the second region of the first ferromagnetic layer is changed. In Example 3, Fe having a thickness of 3.7 Å and Gd having a thickness of 1.3 Å were alternately laminated five times on the intermediate layer to form a second region of the first ferromagnetic layer.

The layer structure of the first ferromagnetic layer in Example 3 is as follows, and the structure of the other layers is the same as that of Example 1.
First ferromagnetic layer: Co _0.24 Fe _0.56 B _0.20 (10 Å) / Mo (5 Å) / [Fe (3.7 Å) / Gd (1.3 Å)] ₅

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

(Example 4)
Example 4 is different from Example 1 in that the configuration of the second region of the first ferromagnetic layer is changed. In Example 4, a FeCo alloy film having a thickness of 3.7 Å and Gd having a thickness of 1.3 Å are alternately laminated five times on the intermediate layer to form a second region of the first ferromagnetic layer. bottom. The FeCo alloy film was formed by co-sputtering (binary simultaneous sputtering) using a Fe target and a Co target.

The layer structure of the first ferromagnetic layer in Example 4 is as follows, and the structure of the other layers is the same as that of Example 1.
First ferromagnetic layer: Co _0.24 Fe _0.56 B _0.20 (10 Å) / Mo (5 Å) / [Fe _0.90 Co _0.10 (3.7 Å) / Gd (1.3 Å)] ₅

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

(Comparative Example 1)
Comparative Example 1 is different from Example 1 in that the configuration of the first ferromagnetic layer is changed. In Comparative Example 1, the intermediate layer and the second region of the first ferromagnetic layer 1 were not formed with respect to Example 1.

The layer structure of the first ferromagnetic layer in Comparative Example 1 is as follows, and the structure of the other layers is the same as that of Example 1.
First ferromagnetic layer: Co _0.24 Fe _0.56 B _0.20 (10 Å)

In Comparative Example 1, the pulsed light was irradiated in the same manner as in Example 1, and the change in the output voltage before and after the irradiation was measured. In the photodetector element according to Comparative Example 1, the change in output voltage before and after irradiation with pulsed light was 2.5 mV.

The results of Examples 1 to 4 and Comparative Example 1 are summarized in the table below. As shown in Table 1, the photodetector elements of Examples 1 to 4 had higher efficiency of converting an optical signal into an electric signal than the photodetector element of Comparative Example 1.

1 ... 1st ferromagnetic layer, 1A ... 1st region, 1B ... 2nd region, 1C ... intermediate layer, 2 ... 2nd ferromagnetic layer, 2A ... 3rd region, 2B ... 4th region, 3 ... spacer layer, 4 ... Third ferromagnetic layer, 5 ... Magnetic coupling layer, 6 ... Underlayer layer, 7 ... Vertical magnetization induced layer, 8 ... Cap layer, 9 ... Side wall insulating layer, 10 ... Optical detection element, 11 ... Signal processing unit, 15 ... 1st electrode, 16 ... 2nd electrode, 20 ... integrated circuit, 30 ... interlayer insulating film, 100 ... receiver, 200 ... transmitter, 201 ... light source, 202 ... electrical signal generation element, 203 ... optical modulation element, 300 ... Transmission / reception device, 500 ... Portable terminal device, 600 ... Information processing device, 1000, 1001, 1002 ... Communication system, FB ... Fiber, _G ... Ground, Is ... Sense current, M1, M2 ... Magnetization, PG ... Reference potential terminal , _Pin ... input terminal, P _out ... output terminal, PS ... power supply, w ... through wiring

Claims (6)

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 are provided.
The first ferromagnetic layer has a first region in contact with the spacer layer and a second region located away from the spacer layer from the first region.
The first region is a CoFeB alloy, and the second region is a photodetector which is a magnetic material mainly containing Fe and Gd as constituent elements. Further having an intermediate layer between the first region and the second region
The photodetector according to claim 1, wherein the intermediate layer contains any one or more elements selected from the group consisting of Mo, Ru, Ta, W, and Pt. The second ferromagnetic layer has a third region in contact with the spacer layer and a fourth region located away from the spacer layer from the third region and containing boron.
The photodetector according to claim 1 or 2, wherein the third region has a lower concentration of boron than the fourth region or does not contain boron. The photodetector according to any one of claims 1 to 3, wherein the first region has a higher concentration of boron than the second region. The photodetector according to claim 3, wherein the third region contains an Fe or CoFe alloy and the crystal structure is a bcc structure. A receiving device having the photodetector according to any one of claims 1 to 5.

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