Optical element

Abstract

The present invention provides a photodetector that can improve heat dissipation and shorten the fall time during photoresponse. [Solution] The photodetector element 100 comprises a magnetic element 10 having a first ferromagnetic layer 1 to which light is irradiated, a second ferromagnetic layer 2, and a spacer layer 3 sandwiched between the first ferromagnetic layer 1 and the second ferromagnetic layer 2; an upper electrode 11 in contact with the upper surface 1a of the first ferromagnetic layer 1 opposite to the spacer layer 3; and a lower electrode 20 in contact with the lower surface 2a of the second ferromagnetic layer 2 opposite to the spacer layer 3. The lower electrode 20 has a narrowed planar shape in the connection region 22 including the portion 20a in contact with the second ferromagnetic layer 2, and includes a heat sink layer 13 of a thickness that functions as a heat sink. The entire magnetic element 10, including the upper electrode 11, is covered with a thermally conductive insulating material 31.

Description

Technical Field

[0001] The present invention relates to a light detection element.

Background Art

[0002] Photoelectric conversion elements such as light detection elements are used in various applications. For example, Patent Document 1 describes a receiving device that receives an optical signal using a photodiode. A photodiode is, for example, a pn junction diode using a semiconductor pn junction, which converts light into an electrical signal.

[0003] Also, for example, Patent Document 2 discloses a light detection element using a magnetic element and a receiving device capable of high-speed optical communication using this light detection element. Patent Document 3 discloses a light detection element using a magnetic element and having excellent heat dissipation, and a receiving device using this light detection element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Figure 10(a) is a cross-sectional view showing the schematic configuration of a photodetector 200 described in Patent Document 3 as an example of a conventional spin photodetector, and Figure 10(b) is a plan view of its lower electrode 120. As shown in Figure 10(a), the photodetector 200 is provided on a substrate 40 in the order of lower electrode 120, magnetic element 10, and upper electrode 11. The magnetic element 10 comprises a first ferromagnetic layer 1, a second ferromagnetic layer 2, a spacer layer 3 sandwiched between the first ferromagnetic layer 1 and the second ferromagnetic layer 2, and a cap layer 4. The sides of the magnetic element 10 are covered with an insulator 25.

[0006] However, the conventional photodetector 200 shown in Figure 10(a) had poor heat dissipation from the top of the photodetector 200 because the air surrounding the upper electrode 11 had very low thermal conductivity.

[0007] Furthermore, in the conventional photodetector 200, as shown in Figure 10(b), the lower electrode 120 receives the entire spot S of light irradiated in a connection region 21 that includes, for example, a portion 120a in contact with the second ferromagnetic layer 2 of the magnetic element 10. The size of the connection region 21 is, for example, 6 μm in width A and 4 μm in height B. The diameter of the light spot S is approximately equal to the wavelength of the irradiated light (500 nm to 1 μm), and the magnetic element 10 (<200 nm) is positioned at the center of the light spot S. The lower electrode 120 has a film thickness of, for example, about 50 nm, and although the lower electrode 120 and the substrate 40 are in contact, a low thermal conductivity alumina layer is actually present, resulting in poor heat dissipation even at the bottom of the photodetector 200.

[0008] Thus, conventional photodetectors have problems such as low thermal conductivity of the material surrounding the magnetic element, and the film thickness of the lower electrode being too thin from the standpoint of heat dissipation, resulting in insufficient heat dissipation overall and a long fall time during the photoresponse.

[0009] This invention has been made in view of the above problems, and aims to provide a photodetector that can improve heat dissipation and shorten the fall time during photoresponse. [Means for solving the problem]

[0010] To achieve the above objective, the photodetector according to the present invention comprises a magnetic element having 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; an upper electrode in contact with the first surface of the first ferromagnetic layer opposite to the spacer layer; and a lower electrode in contact with the second surface of the second ferromagnetic layer opposite to the spacer layer, wherein the lower electrode has a narrowed planar shape in the region including the portion in contact with the second ferromagnetic layer and includes a heat sink layer of a thickness that functions as a heat sink; and the entire magnetic element, including the upper electrode, is covered with a thermally conductive insulating material.

[0011] This configuration allows the photodetector element of the present invention to reduce excess heat generation from the metal portion surrounding the magnetic element by narrowing the lower electrode, thereby improving heat dissipation efficiency. Furthermore, the lower electrode has a heat sink layer, which efficiently dissipates heat accumulated in the magnetic element. In addition, covering the entire magnetic element, including the upper electrode, with a thermally conductive insulating material increases the overall heat dissipation efficiency of the magnetic element. By improving heat dissipation in this way, the photoresponse performance can be improved, and in particular, the fall time during the photoresponse can be shortened.

[0012] In the photodetector according to the present invention, the width of the constriction of the lower electrode may be smaller than the spot diameter of the irradiated light.

[0013] With this configuration, the photodetector element of the present invention can suppress excess heat generation from the lower electrode because, by making the narrowing width of the lower electrode less than or equal to the diameter of the irradiated light spot, a portion of the irradiated light passes through without hitting the lower electrode.

[0014] The photodetector according to the present invention may be configured such that the lower electrode has a substrate on the side opposite to the magnetic element, and a layer containing the same or a different thermally conductive insulating material as the thermally conductive insulating material is provided between the lower electrode and the substrate.

[0015] With this configuration, in the photosensing element of the present invention, since the thermally conductive insulating material exists between the substrate and the lower electrode, effective heat dissipation from the magnetic element can be achieved.

[0016] In the photosensing element according to the present invention, the upper electrode may have a light-transmissive configuration.

[0017] With this configuration, in the photosensing element of the present invention, since the upper electrode is transparent to light of the used wavelength, light can be delivered to the magnetic element.

[0018] In the photosensing element according to the present invention, the film thickness of the heat sink layer may be 100 nm or more and 1000 nm or less.

[0019] With this configuration, in the photosensing element of the present invention, the heat sink layer can secure a sufficient heat capacity as a heat bath.

[0020] In the photosensing element according to the present invention, the thermally conductive insulating material may contain either one or both of AlN and AlON.

[0021] With this configuration, in the photosensing element of the present invention, by using an insulating material having high thermal conductivity as the thermally conductive insulating material, the heat dissipation performance can be improved and light transmissivity can be imparted.

[0022] In the photosensing element according to the present invention, the heat sink layer may include either one or both of Ru and Cu layers, or a laminated film of Cu and a metal other than Cu.

[0023] With this configuration, in the photosensing element of the present invention, the heat sink layer can withstand a 400 °C high-temperature annealing for a magnetic element such as a MTJ element.

[0024] In the photosensor element according to the present invention, the lower electrode includes a seed layer on the side in contact with the magnetic element and a heat sink layer in contact with the surface of the seed layer opposite to the magnetic element, and the seed layer may include a layer of either Ru or Cu or both, or a laminated film of Cu and a metal other than Cu.

[0025] With this configuration, the photosensor element of the present invention can withstand a high-temperature annealing at 400°C for the seed layer with respect to a magnetic element such as an MTJ element.

Effect of the Invention

[0026] According to the present invention, it is possible to provide a photosensor element capable of improving heat dissipation and shortening the fall time during light response.

Brief Description of the Drawings

[0027] [Figure 1] It is a cross-sectional view showing the configuration of a photosensor element according to an embodiment of the present invention. [Figure 2] (a) is a plan view of the lower electrode, and (b) is a perspective view thereof. [Figure 3] It is a diagram showing how the direction (tilt angle) of the magnetization M1 of the first ferromagnetic layer of the magnetic element changes in response to a change in the intensity of the irradiated light. [Figure 4] It is a diagram showing the results of simulating the temperature distribution inside the photosensor element for four models with different structures. [Figure 5] It is a graph showing the time change of the temperature in the first ferromagnetic layer of the magnetic element for four models with different structures. [Figure 6] It is a table showing the fall time of the temperature in the first ferromagnetic layer of the magnetic element for four models with different structures. [Figure 7] (a) is a cross-sectional view showing the structure of a model in which the heat sink layer is Ru, and (b) is a graph showing the results of simulating the time change of the temperature in the first ferromagnetic layer of the magnetic element by changing the thickness of the heat sink layer. [Figure 8](a) is a cross-sectional view showing the structure of a model where the heat sink layer is made of Cu, and (b) is a graph showing the results of simulating the time change of temperature in the first ferromagnetic layer of the magnetic element by changing the thickness of the heat sink layer. [Figure 9] This graph compares the time-dependent temperature change at the first ferromagnetic layer of a magnetic element when the heat sink layer is made of Ru and when it is made of Cu. [Figure 10] (a) is a cross-sectional view showing the configuration of a conventional photodetector, and (b) is a plan view of its lower electrode. [Modes for carrying out the invention]

[0028] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for ease of understanding, the scale of the parts in the drawings may differ from the actual scale. In the xyz Cartesian coordinate system set in the drawings, the x-axis and y-axis directions are horizontal, and the z-axis direction is vertical. The positive z-axis direction is also called the upward direction, and the negative z-axis direction is also called the downward direction, but this is unrelated to the direction of gravity. A degree of deviation is permissible in directions such as parallel, perpendicular, orthogonal, horizontal, vertical, up and down, and left and right, as long as it does not impair the effects of the embodiment. Furthermore, the "~" indicating a numerical range means that the values ​​written before and after it are included as the lower and upper limits, respectively.

[0029] [First Embodiment] First, a first embodiment of the present invention will be described.

[0030] (composition) Figure 1 is a cross-sectional view showing the configuration of a photodetector 100 according to a first embodiment of the present invention. As shown in Figure 1, the photodetector 100 comprises a photoreactive magnetic element (hereinafter also referred to as a magnetic element) 10, an upper electrode 11, and a lower electrode 20 on a substrate 40. The magnetic element 10 comprises a first ferromagnetic layer 1 to which light is irradiated, a second ferromagnetic layer 2, and a spacer layer 3 sandwiched between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The upper electrode 11 is provided so as to be in contact with the upper surface 1a of the first ferromagnetic layer 1 opposite to the spacer layer 3. The lower electrode 20 is provided so as to be in contact with the lower surface 2a of the second ferromagnetic layer 2 opposite to the spacer layer 3. The lower electrode 20 has a narrowed planar shape in the connection region 22 including the portion 20a of the magnetic element 10 that is in contact with the second ferromagnetic layer 2, and includes a heat sink layer 13 of a thickness that functions as a heat sink. The entire magnetic element 10, including the upper electrode 11, is covered with a thermally conductive insulating material 31.

[0031] Light incident on the photodetector element 100 is directed onto the magnetic element 10. The magnetic element 10 detects the light directed onto it. The magnetic element 10 converts the light directed onto it into an electrical signal. The photodetector element 100 may include a lens that focuses the light toward the magnetic element 10. If a lens is included, the magnetic element 10 is positioned, for example, at the focal point of the light focused by the lens. The photodetector element 100 may be columnar, for example, prismatic, cylindrical, or the like.

[0032] The term "light" as used herein is not limited to visible light, but may also include infrared radiation with a longer wavelength than visible light, or ultraviolet radiation with a shorter wavelength than visible light. The wavelength of visible light is, for example, 380 nm or more and less than 800 nm. The wavelength of infrared radiation is, for example, 800 nm or more and less than 1 mm. The wavelength of ultraviolet radiation is, for example, 200 nm or more and less than 380 nm.

[0033] The following describes each component.

[0034] (Magnetic element) The magnetic element 10 comprises at least a first ferromagnetic layer 1, a second ferromagnetic layer 2, and a spacer layer 3 sandwiched between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. In Figure 1, the second ferromagnetic layer 2, the spacer layer 3, and the first ferromagnetic layer 1 are stacked in this order in the positive z-axis direction to form a laminate 15. The laminate 15 constituting the magnetic element 10 may further include other layers as needed, such as a third ferromagnetic layer, a buffer layer, a seed layer, a magnetic coupling layer, and a perpendicular magnetization induction layer.

[0035] As shown in Figure 1, an upper electrode 11 is formed on the upper part of the laminate 15, and a lower electrode 20 is formed on the lower part of the laminate 15. When referring to the magnetic element 10, the upper electrode 11 and lower electrode 20 may be included in addition to the laminate 15.

[0036] The magnetic 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 magnetic element 10 can exhibit the tunnel magnetoresistance (TMR) effect. The resistance value of the magnetic element 10 changes when light is irradiated from the outside. The resistance value in the z-axis direction (resistance value when current is passed in the z-axis direction) of the magnetic element 10 changes in accordance with the relative change between the magnetization M1 state of the first ferromagnetic layer 1 and the magnetization M2 state of the second ferromagnetic layer 2. For example, the resistance value in the z-axis direction of the magnetic element 10 changes in accordance with the change in the relative angle between the direction of magnetization M1 of the first ferromagnetic layer 1 and the direction of magnetization M2 of the second ferromagnetic layer 2. Also, for example, the resistance value in the z-axis direction of the magnetic element 10 changes in accordance with the change in the magnitude of magnetization M1 of the first ferromagnetic layer 1.

[0037] Furthermore, for example, if the spacer layer 3 is made of metal, the magnetic element 10 can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element. Even when the magnetic element 10 is a GMR element, the resistance value in the z-axis direction (the resistance value when current is passed in the z-axis direction) changes according to the relative change between the magnetization M1 state of the first ferromagnetic layer 1 and the magnetization M2 state of the second ferromagnetic layer 2. Depending on the constituent material of the spacer layer 3, the magnetic element 10 may be called an MTJ element, a GMR element, etc., but it is collectively called a magnetoresistance effect element. The overall thickness of the magnetic element 10 is, for example, 15 nm to 40 nm.

[0038] The magnetic element 10 has to be a ferromagnetic material whose magnetization state changes upon irradiation with light, and whose resistance value changes in accordance with the change in magnetization state. For example, in addition to the MTJ element and GMR element described above, anisotropic magnetoresistance (AMR) effect element, colossal magnetoresistance (CMR) effect element, etc. can be used as the magnetic element 10.

[0039] When light is incident on the photodetector 100 through the lens, the magnetic element 10 is positioned at the focal point of the light in the usable band focused by the lens. Preferably, the focal point of the light in the usable band overlaps with the first ferromagnetic layer 1. For example, when using visible light, the magnetic element 10 is positioned at the focal point of a specific wavelength range within the wavelength range of 380 nm to less than 800 nm. Alternatively, when using infrared light, the magnetic element 10 is positioned at the focal point of a specific wavelength range within the wavelength range of 800 nm to 1 mm. Alternatively, when using ultraviolet light, the magnetic element 10 is positioned at the focal point of a specific wavelength range within the wavelength range of 200 nm to less than 380 nm.

[0040] <First ferromagnetic layer> The first ferromagnetic layer 1 is a photosensitive layer whose magnetization state changes when light is irradiated from the outside. The first ferromagnetic layer 1 is also called the magnetization free layer. The magnetization free layer is a layer containing a magnetic material whose magnetization state changes when a predetermined external energy is applied. The predetermined external energy is, for example, light irradiated from the outside, a current flowing in the z-axis direction of the magnetic element 10, or an external magnetic field. The magnetization M1 of the first ferromagnetic layer 1 changes state according to the intensity of the irradiated light.

[0041] The first ferromagnetic layer 1 contains a ferromagnetic material. The first ferromagnetic layer 1 contains at least one of the magnetic elements such as Co, Fe, or Ni. The first ferromagnetic layer 1 may also contain elements such as B, Mg, Hf, and Gd along with the magnetic elements mentioned above. The first ferromagnetic layer 1 may be an alloy containing a magnetic element and a non-magnetic element, for example. The first ferromagnetic layer 1 may be composed of multiple layers. The first ferromagnetic layer 1 may be, for example, a CoFeB alloy, a laminate in which a CoFeB alloy layer is sandwiched between Fe layers, or a laminate in which a CoFeB alloy layer is sandwiched between CoFe layers. Generally, "ferromagnetism" includes "ferrimagnetism". The first ferromagnetic layer 1 may exhibit ferrimagnetism. Alternatively, the first ferromagnetic layer 1 may exhibit ferromagnetism that is not ferrimagnetism. For example, a CoFeB alloy exhibits ferromagnetism that is not ferrimagnetism.

[0042] The first ferromagnetic layer 1 may be an in-plane magnetized film having an easy magnetization axis in the direction within the film plane (any direction in the xy plane), or a perpendicular magnetized film having an easy magnetization axis in the direction perpendicular to the film plane (in the z-axis direction).

[0043] The thickness of the first ferromagnetic layer 1 is, for example, 1 nm to 5 nm. Preferably, the thickness of the first ferromagnetic layer 1 is, for example, 1 nm to 2 nm. When the first ferromagnetic layer 1 is a perpendicular magnetization film, if the thickness of the first ferromagnetic layer 1 is thin, the effect of perpendicular magnetic anisotropy applied from the layers above and below the first ferromagnetic layer 1 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 increases. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high, the force that causes the magnetization M1 to return to the z-axis direction is strengthened. On the other hand, if the thickness of the first ferromagnetic layer 1 is thick, the effect of perpendicular magnetic anisotropy applied from the layers above and below the first ferromagnetic layer 1 is relatively weakened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is weakened.

[0044] When the thickness of the first ferromagnetic layer 1 decreases, its volume as a ferromagnetic material decreases, and when its thickness increases, its volume as a ferromagnetic material increases. The reactivity of the magnetization of the first ferromagnetic layer 1 when external energy is applied is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and volume (V) of the first ferromagnetic layer 1. In other words, when the product of the magnetic anisotropy and volume of the first ferromagnetic layer 1 decreases, its reactivity to light increases. From this viewpoint, in order to increase the reactivity to light, it is preferable to appropriately design the magnetic anisotropy of the first ferromagnetic layer 1 and then reduce the volume of the first ferromagnetic layer 1.

[0045] If the thickness of the first ferromagnetic layer 1 is greater than 2 nm, an insertion layer made of, for example, Mo and W may be provided within the first ferromagnetic layer 1. That is, the first ferromagnetic layer 1 may be a laminate in which a ferromagnetic layer, an insertion layer, and a ferromagnetic layer are stacked in order in the z-axis direction. The interfacial magnetic anisotropy at the interface between the insertion layer and the ferromagnetic layer increases the perpendicular magnetic anisotropy of the entire first ferromagnetic layer 1. The thickness of the insertion layer is, for example, 0.1 nm to 1.0 nm.

[0046] <Second ferromagnetic layer> The second ferromagnetic layer 2 is a magnetization-fixed layer. The magnetization-fixed layer is a layer made of a magnetic material whose magnetization state changes less easily than that of the magnetization-free layer when a predetermined external energy is applied. For example, the magnetization direction of the magnetization-fixed layer changes less easily than that of the magnetization-free layer when a predetermined external energy is applied. Also, for example, the magnitude of magnetization of the magnetization-fixed layer changes less easily than that of the magnetization-free layer when a predetermined external energy is applied. The coercivity of the second ferromagnetic layer 2 is greater than that of the first ferromagnetic layer 1, for example. The second ferromagnetic layer 2 has an easy magnetization axis in the same direction as the first ferromagnetic layer 1, for example. The second ferromagnetic layer 2 may be an in-plane magnetized film or a perpendicular magnetized film.

[0047] The material constituting the second ferromagnetic layer 2 is, for example, the same as that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be a multilayer film in which Co with a thickness of 0.4 nm to 1.0 nm and Pt with a thickness of 0.4 nm to 1.0 nm are alternately stacked several times. The second ferromagnetic layer 2 may also be a laminate in which Co with a thickness of 0.4 nm to 1.0 nm, Mo with a thickness of 0.1 nm to 0.5 nm, a CoFeB alloy with a thickness of 0.3 nm to 1.0 nm, and Fe with a thickness of 0.3 nm to 1.0 nm are stacked in that order.

[0048] <Spacer layer> The spacer layer 3 is a layer placed between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The spacer layer 3 is composed of a conductor, an insulator, or a semiconductor, or a layer containing a current-carrying point composed of a conductor within an insulator. For example, the spacer layer 3 is a non-magnetic layer. The thickness of the spacer layer 3 can be adjusted according to the orientation direction of the magnetization of the first ferromagnetic layer 1 and the magnetization of the second ferromagnetic layer 2 in the initial state described later.

[0049] When the spacer layer 3 is composed of an insulating material, materials containing aluminum oxide, magnesium oxide, titanium oxide, or silicon oxide can be used as the material for the spacer layer 3. These insulating materials may also contain elements such as Al, B, Si, and Mg, or magnetic elements such as Co, Fe, and Ni. A high rate of change in magnetoresistance 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 around 0.5 nm to 5.0 nm, or around 1.0 nm to 2.5 nm.

[0050] When the spacer layer 3 is made of a non-magnetic conductive material, conductive materials 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 around 0.5 nm to 5.0 nm, or around 2.0 nm to 3.0 nm.

[0051] When the spacer layer 3 is made of a non-magnetic semiconductor material, materials such as zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, or indium tin oxide (ITO) can be used. In this case, the film thickness of the spacer layer 3 may be approximately 1.0 nm to 4.0 nm.

[0052] When a layer containing current-carrying points composed of conductors in a non-magnetic insulator is applied as the spacer layer 3, the structure may include current-carrying points composed of non-magnetic conductors such as Cu, Au, and Al in a non-magnetic insulator composed of aluminum oxide or magnesium oxide. Alternatively, the conductors may be composed of magnetic elements such as Co, Fe, and Ni. In this case, the film thickness of the spacer layer 3 may be about 1.0 nm to 2.5 nm. The current-carrying points are, for example, columnar bodies with a diameter of 1 nm to 5 nm when viewed from a direction perpendicular to the film surface.

[0053] <Top electrode> The upper electrode 11 is positioned, for example, so as to be in contact with the upper surface 1a of the first ferromagnetic layer 1 opposite to the spacer layer 3. Incident light is irradiated onto the magnetic element 10 from the upper electrode 11 side and irradiates at least the first ferromagnetic layer 1. The upper electrode 11 is made of a conductive material. The upper electrode 11 is, for example, a transparent electrode that is transparent to light in the wavelength range used. Preferably, the upper electrode 11 transmits 80% or more of the light in the wavelength range used. The upper electrode 11 is an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). The upper electrode 11 may have a configuration in which a plurality of columnar metals are contained within the transparent electrode material of these oxides.

[0054] It is not essential to use a transparent electrode material as the upper electrode 11; a thin film of a metallic material such as Au, Cu, or Al may be used to allow the irradiated light to reach the first ferromagnetic layer 1. When a metal is used as the material for the upper electrode 11, the film thickness of the upper electrode 11 is, for example, 3 nm to 10 nm. The upper electrode 11 may also have an anti-reflective coating on the irradiated surface to which light is irradiated.

[0055] <Lower electrode> The lower electrode 20 includes a seed layer (also called the lower electrode layer) 12 on the side in contact with the magnetic element 10, and a heat sink layer 13 in contact with the lower surface 12a of the seed layer 12 on the side opposite to the magnetic element 10. The seed layer 12 of the lower electrode 20 is arranged, for example, to be in contact with the lower surface 2a of the second ferromagnetic layer 2 on the side opposite to the spacer layer 3. The seed layer 12 is made of a conductive material. The seed layer 12 includes, for example, a layer of either Ru or Cu, or both, or a laminated film of Cu and a metal other than Cu. Furthermore, the seed layer 12 may be, for example, a multilayer film of Ru and Cu and Ru and Cu and Ru, a multilayer film of Ru and Cu and Cu and Ru, a multilayer film of Cu having a face-centered cubic (fcc) structure and Co having a body-centered cubic (bcc) structure, a multilayer film of Cu having an fcc structure and Mo or W having a bcc structure, a multilayer film of Cu and Mo, a multilayer film of Cu and Co and Mo, or a multilayer film of Cu and Co and Mo having a bcc structure. The multilayer film of Ru and Cu and Ru may, in terms of thickness, be, for example, a multilayer film of Ru (7.5 nm), Cu (7.5 nm), Cu (7.5 nm), and Ru (7.5 nm) (total thickness 30 nm); the multilayer film of Cu and Mo may, in terms of thickness, be a multilayer film of Cu (15 nm) and Mo (5 nm); and the multilayer film of Cu, Co, and Mo having a bcc structure may, in terms of thickness, be a multilayer film of Cu (20 nm), Co (5 nm), and Mo having a bcc structure (5 nm). Furthermore, the seed layer 12 may consist of layers of Ta or Ti above and below these metallic Ru and Cu. In addition, multilayer films of Cu and Ta, Ta, Cu, and Ti, and Ta, Cu, and TaN may be used. Furthermore, TiN or TaN may be used as the seed layer 12. The seed layer 12 is, for example, Ru with a thickness of 50 nm (500 Å).

[0056] Figure 2(a) is a plan view of the lower electrode 20, and Figure 2(b) is a perspective view thereof. As shown in Figure 2, the lower electrode 20 has a narrowed plan view shape in the connection region 22, which includes, for example, a portion 20a that contacts the second ferromagnetic layer 2 of the magnetic element 10. The width SW of the narrowing of the lower electrode 20 is smaller than the diameter of the spot S of the irradiated light L. In the connection region 22 of the lower electrode 20, the portion 20a that contacts the second ferromagnetic layer 2 of the magnetic element 10 is located, for example, in the center of the narrowing width and also in the center of the spot S of the irradiated light L.

[0057] The lower electrode 20 includes, for example, a heat sink layer 13 of a thickness that functions as a heat sink. The heat sink layer 13 includes, for example, a layer of either Ru, Cu, or both, or a laminated film of Cu and a metal other than Cu. The material constituting the heat sink layer 13 may be the same as or different from that of the seed layer 12. The heat sink layer 13 may be, for example, a laminated film of Ru and Cu and Ru and Cu and Ru, a laminated film of Cu having an fcc structure and Co having a bcc structure, a laminated film of Cu and Mo or W having a bcc structure, a laminated film of Cu and Mo, a laminated film of Cu, Co and Mo, or a laminated film of Cu, Co and Mo having a bcc structure. The laminated film of Ru and Cu and Cu and Ru may be a laminated film of Ru (7.5 nm), Cu (7.5 nm), Cu (7.5 nm), and Ru (7.5 nm) with a total film thickness of 30 nm, the laminated film of Cu and Mo may be a laminated film of Cu (15 nm) and Mo (5 nm) with a film thickness, and the laminated film of Cu, Co, and Mo having a bcc structure may be a laminated film of Cu (20 nm), Co (5 nm), and Mo having a bcc structure (5 nm) with a film thickness. In addition, the heat sink layer 13 may have Ta or Ti laminated above and below these metallic Ru and Cu. Alternatively, a laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN may be used. Additionally, TiN or TaN may be used as the seed layer 12. The film thickness of the heat sink layer 13 is, for example, 100 nm to 1000 nm.

[0058] (Thermal conductive insulating layer) The thermally conductive insulating layer 31 is provided to cover the entire magnetic element 10, including the upper electrode 11. A substrate 40 is provided on the side of the lower electrode 20 opposite to the magnetic element 10, and a thermally conductive insulating layer 32, made of the same or different material as the thermally conductive insulating layer 31, is provided between the lower electrode 20 and the substrate 40. The thermally conductive insulating layers 31 and 32 are, for example, insulators. The thermally conductive insulating layers 31 and 32 include, for example, AlN, AlON, or both. The thermally conductive insulating layers 31 and 32 have, for example, a higher thermal conductivity than the magnetic element 10. The thermally conductive insulating layers 31 and 32 have, for example, a higher thermal conductivity than the upper electrode 11. The thermally conductive insulating layers 31 and 32 have, for example, a higher thermal conductivity than the lower electrode 20. The thermal conductivity of the thermally conductive insulating layers 31 and 32 is, for example, greater than 40 W / m·K. A portion of the heat generated in the magnetic element 10, the upper electrode 11, and the lower electrode 20 is dissipated through the thermally conductive insulating layers 31 and 32.

[0059] The thermally conductive insulating layer 31 transmits light in the operating wavelength range. Preferably, the thermally conductive insulating layer 31 transmits 80% or more of the light in the operating wavelength range.

[0060] As described above, the photodetector 100 according to the first embodiment can convert light into an electrical signal by replacing the light irradiated onto the magnetic element 10 with an output voltage from the magnetic element 10. Furthermore, the presence of highly thermally conductive insulating layers 31 and 32 on the outside of the magnetic element 10, which generates heat when irradiated with light, promotes heat dissipation from the magnetic element 10. In other words, after the irradiation of the first ferromagnetic layer 1 with light stops, the magnetic element 10 cools down quickly, and the recovery to the initial state of magnetization M1 is rapid. A faster return of the magnetization M1 of the first ferromagnetic layer 1 to the initial state improves the response characteristics of the photodetector 100 to light. In other words, the response of the photodetector 100 to light becomes faster.

[0061] (Heat dissipation performance) Figure 4 shows the results of simulating the temperature distribution inside the photodetector element 100 at a predetermined time after irradiation with short-pulse light for four different structural models. (1) Model 1 is a conventional example and has a structure that sequentially includes an insulating layer 14 (k-Al2O3, thermal conductivity 6.9 W / m·K), a lower electrode layer 12 (Ru, thickness 50 nm), a magnetic element 10, and an upper electrode 11 in the positive z-axis direction. The area around the magnetic element 10 is filled with the insulating layer 14. (2) Model 2 has a structure that sequentially includes a thermally conductive insulating layer 32 (AlN, thermal conductivity 46.5 W / m·K), a lower electrode layer 12 (Ru, thickness 50 nm), a magnetic element 10, and an upper electrode 11 in the positive z-axis direction. The area around the magnetic element 10 is filled with an insulating layer 14. (3) Model 3 has a structure that sequentially includes a thermally conductive insulating layer 32 (AlN, thermal conductivity 46.5 W / m·K), a heat sink layer 13 (Ru, thickness 200 nm), a lower electrode layer 12 (Ru, thickness 50 nm), a magnetic element 10, and an upper electrode 11 in the positive z-axis direction. The area around the magnetic element 10 is filled with an insulating layer 14. (4) Model 4 includes, in the positive z-axis direction, a thermally conductive insulating layer 32 (AlN, thermal conductivity 46.5 W / m·K), a heat sink layer 13 (Ru, thickness 200 nm), a lower electrode layer 12 (Ru, thickness 50 nm), a magnetic element 10, and an upper electrode 11 in that order, and the lower electrode 20, which consists of the lower electrode layer 12 and the heat sink layer 13, has a constricted portion 23. The area around the magnetic element 10 is filled with an insulating layer 14.

[0062] As can be seen from Figure 4, the temperature around the magnetic element 10 decreases and the temperature rise range narrows in the following order: Model 1, a conventional example; Model 2, which has an AlN thermal conductive insulating layer 32; Model 3, which has an AlN thermal conductive insulating layer 32 and a heat sink layer 13; and Model 4, which has an AlN thermal conductive insulating layer 32 and a heat sink layer 13 and a constricted portion 23 in the lower electrode 20. In other words, in terms of heat dissipation, Model 4 is the best, followed by Model 3, then Model 2, and Model 1 is the worst.

[0063] Figure 5 shows the results of a simulation of the time change in temperature of the first ferromagnetic layer 1 of the magnetic element 10 when irradiated with short-pulse light for five different structural models. Models 1 to 4 are the same as in Figure 4. Model 5 is the same as Model 4, but the Ru heat sink layer 13 is replaced with a Cu heat sink layer 13. That is, Model 5 sequentially includes a thermally conductive insulating layer 32 (AlN, thermal conductivity 46.5 W / m·K), a heat sink layer 13 (Cu, thickness 200 nm), a lower electrode layer 12 (Ru, thickness 50 nm), a magnetic element 10, and an upper electrode 11 in the positive z-axis direction, and the lower electrode 20, consisting of the lower electrode layer 12 and the heat sink layer 13, has a constricted portion 23.

[0064] Figure 6 is a table showing the fall time for each model in Figure 5, from the state where the temperature rises due to irradiation with short-pulse light until it drops to half its original temperature.

[0065] As can be seen from Figures 5 and 6, the temperature fall-down time decreases in the following order: Model 1 (conventional example), Model 2 (AlN thermal conductive insulating layer 32), Model 3 (AlN thermal conductive insulating layer 32 and heat sink layer 13), Model 4 (AlN thermal conductive insulating layer 32 and Ru heat sink layer 13 with a constricted portion 23 on the lower electrode 20), and Model 5 (AlN thermal conductive insulating layer 32 and Cu heat sink layer 13 with a constricted portion 23 on the lower electrode 20). In other words, in terms of heat dissipation, Model 5 is the best, followed by Model 4, then Model 3, then Model 2, and Model 1 is the worst.

[0066] Figure 7(a) is a cross-sectional view showing the structure of Model 6, in which the heat sink layer 13-1 is made of Ru, and Figure 7(b) is a graph showing the results of simulating the time change in temperature of the first ferromagnetic layer 1 of the magnetic element 10 by changing the thickness of the heat sink layer 13-1 of Model 6. As shown in Figure 7(a), in Model 6, a Ru heat sink layer 13-1, a 50 nm thick lower electrode layer 12 made of Ru, a magnetic element 10, an upper electrode 11 made of ITO, and an Al2O3 insulating layer 14 are stacked in order in the positive z-axis direction, and an Al2O3 insulating layer 14 is also embedded around the magnetic element 10.

[0067] As shown in Figure 7(b), the temperature fall time decreases as the thickness of the heat sink layer 13-1 increases compared to the case without a heat sink layer (solid line). However, when the thickness of the heat sink layer 13-1 exceeds 300 nm, the heat sink effect appears to saturate. When there is a Ru heat sink layer 13-1, the fall rate (based on -50%) is 150 ps. The film thickness of the heat sink layer 13-1 may be between 100 nm and 1000 nm, and preferably 200 nm.

[0068] Figure 8(a) is a cross-sectional view showing the structure of Model 7, in which the heat sink layer 13-2 is made of Cu, and Figure 8(b) is a graph showing the results of simulating the time change in temperature of the first ferromagnetic layer 1 of the magnetic element 10 by changing the thickness of the heat sink layer 13-2 of Model 7. As shown in Figure 8(a), Model 7 is the same as Model 6 in Figure 7(a), but with the Ru heat sink layer 13-1 replaced by the Cu heat sink layer 13-2.

[0069] As shown in Figure 8(b), the temperature fall time decreases as the thickness of the heat sink layer 13-2 increases compared to the case without a heat sink layer (solid line). However, similar to Model 7 for the Ru heat sink layer 13-1, the heat sink effect appears to saturate when the thickness of the Cu heat sink layer 13-2 exceeds 300 nm. When the heat sink layer 13-2 is Cu, the fall time (-50% reference) is 100 ps, ​​which is faster than when the heat sink layer 13-1 is Ru. The film thickness of the heat sink layer 13-2 may be between 100 nm and 1000 nm, and preferably 200 nm.

[0070] Figure 9 is a graph comparing the time-dependent temperature change at the magnetic element 10 when the heat sink layer 13 (film thickness 200 nm) is made of Ru and when it is made of Cu. For comparison, the case without a heat sink layer (solid line) is also shown. The fall rate is faster when the heat sink layer 13 is made of Cu than when it is made of Ru. Therefore, if the magnetic element 10 can withstand annealing at 400°C, the Cu heat sink layer 13 is preferable.

[0071] (Manufacturing process) The photodetector element 100 is obtained by sequentially fabricating a thermally conductive insulating layer 32, a heat sink layer 13, a lower electrode layer (seed layer) 12, a magnetic element 10, an upper electrode 11, and a thermally conductive insulating layer 31 on a substrate 40.

[0072] The magnetic element 10 is manufactured by processes such as lamination, annealing, and processing of each layer. First, a thermally conductive insulating layer 32, a heat sink layer 13, a lower electrode layer 12, a second ferromagnetic layer 2, a spacer layer 3, and a first ferromagnetic layer 1 are laminated on a Si substrate 40 in that order. Each layer is deposited, for example, by sputtering.

[0073] Next, the laminated film is annealed. The annealing temperature is, for example, 250°C to 400°C. After that, the laminated film is processed into a columnar laminate 15 by photolithography and etching (ion milling, etc.). The laminate 15, or each layer, may be mesa-shaped, cylindrical, prismatic, frustoconical, or truncated pyramidal. The shortest width of the laminate 15 when viewed from the z-axis direction is, for example, 10 nm to 1000 nm.

[0074] Next, a thermally conductive insulating layer 31 is formed to cover the sides of the laminate 15. The thermally conductive insulating layer 31 may be laminated multiple times. Then, the upper surface 1a of the first ferromagnetic layer 1 is exposed from the thermally conductive insulating layer 31 by chemical mechanical polishing, and an upper electrode layer is deposited on the first ferromagnetic layer 1 and the thermally conductive insulating layer 31 by sputtering. The upper electrode layer is processed into a columnar or plate-shaped upper electrode 11, such as a cylindrical, prismatic, frustoconical, or pyramidal shape, by photolithography and etching. Then, the thermally conductive insulating layer 31 is embedded around and above the upper electrode 11. A photodetector element 100 is obtained by the above process. In this way, the photodetector element 100 can be continuously formed by a vacuum deposition process.

[0075] (Operation instructions) Next, the operation of the photodetector 100 according to the first embodiment will be described.

[0076] Figure 3 shows how the direction (tilt angle) of the magnetization M1 of the first ferromagnetic layer 1 of the magnetic element 10 changes in response to changes in the intensity of the irradiated light. In Figure 3, (a) shows the magnetization state of the magnetic element 10 in its initial state, and (b) shows the magnetization state of the magnetic element 10 when light L is incident on the photodetector 100. As shown in Figure 3(a), in the initial state, for example, the magnetization M1 of the first ferromagnetic layer 1 is upward, and the magnetization M2 of the second ferromagnetic layer 2 is downward, and the two are antiparallel. As shown in Figure 3(b), when light L is irradiated onto the magnetic element 10, for example, the direction of the magnetization M1 of the first ferromagnetic layer 1 tilts, and the electrical resistance value in the vertical direction of the magnetic element 10 changes. This is detected as a change in voltage between the upper electrode 11 and the lower electrode 20.

[0077] In detail, light focused through a lens (not shown) forms a light spot S at the focal point of the lens and irradiates the magnetic element 10 of the photodetector element 100. The focal point of the lens is located at the magnetic element 10, preferably the first ferromagnetic layer 1.

[0078] When the intensity of light irradiated onto the first ferromagnetic layer 1 changes, the state of magnetization M1 of the first ferromagnetic layer 1 changes. The state of magnetization M1 refers to, for example, the tilt angle of magnetization M1 with respect to the z-axis direction, the magnitude of magnetization M1, etc.

[0079] For example, when the intensity of light irradiated onto the first ferromagnetic layer 1 increases, the magnetization M1 of the first ferromagnetic layer 1 tilts from its initial state due to the external energy from the light irradiation. The angle between the direction of the magnetization M1 of the first ferromagnetic layer 1 when it is not irradiated with light and the direction of the magnetization M1 when it is irradiated with light is, for example, greater than 0° and less than 90°. Alternatively, for example, when the intensity of light irradiated onto the first ferromagnetic layer 1 increases, the magnitude of the magnetization M1 decreases.

[0080] When the magnetization M1 state of the first ferromagnetic layer 1 changes, the resistance value of the magnetic element 10 in the z-axis direction changes due to the magnetoresistance effect. When a constant current (sense current) is passed through the magnetic element 10 in the positive or negative z-axis direction using the upper electrode 11 and the lower electrode 20, an output voltage is obtained from the magnetic element 10. In other words, when the magnetization M1 state of the first ferromagnetic layer 1 changes, the output voltage from the magnetic element 10 also changes.

[0081] The intensity of light irradiated onto the first ferromagnetic layer 1 may take two values, for example, a first intensity and a second intensity. The first intensity may also be zero when the intensity of light irradiated onto the first ferromagnetic layer 1 is zero. Furthermore, the intensity of light irradiated onto the first ferromagnetic layer 1 may take multiple values, or it may change in an analog manner. If the intensity of the incident light takes multiple values, the output voltage of the magnetic element 10 may also take multiple values, and if the intensity of the light changes in an analog manner, the output voltage of the magnetic element 10 may also change in an analog manner. The photodetector element 100 can read out the differences in these output voltages (resistance values) as binary, multi-level, or analog data.

[0082] In the state in which the first ferromagnetic layer 1 is irradiated with light of a first intensity (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 may be in a parallel or antiparallel relationship, and the magnetizations M1 and M2 may be orthogonal.

[0083] If magnetizations M1 and M2 are parallel in the initial state, a sense current is passed from the first ferromagnetic layer 1 towards the second ferromagnetic layer 2. By passing the sense current in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the same direction as the magnetization M2 of the second ferromagnetic layer 2, causing magnetizations M1 and M2 to be parallel in the initial state. Furthermore, by passing the sense current in this direction, it is possible to prevent the magnetization M1 of the first ferromagnetic layer 1 from reversing during operation.

[0084] If magnetizations M1 and M2 are antiparallel in the initial state, it is preferable to flow the sense current from the second ferromagnetic layer 2 towards the first ferromagnetic layer 1. By flowing the sense current in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the opposite direction to that of the magnetization M2 of the second ferromagnetic layer 2, causing magnetizations M1 and M2 to become antiparallel in the initial state.

[0085] As described above, as shown in Figure 3(a), when the intensity of light irradiated onto the first ferromagnetic layer 1 is the first intensity (zero in this example), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are antiparallel and in their initial state. Next, as shown in Figure 3(b), when the intensity of light irradiated onto the first ferromagnetic layer 1 changes to the second intensity, the magnetization M1 of the first ferromagnetic layer 1 tilts from its initial state. Next, as shown in Figure 3(c), when the intensity of light irradiated onto the first ferromagnetic layer 1 returns to the first intensity (zero), the spin transfer torque acts due to the sense current, or the magnetization M1 of the first ferromagnetic layer 1 returns to its original state due to the effect of magnetic anisotropy, and the magnetic element 10 returns to its initial state.

[0086] In this way, the photodetector 100 according to the first embodiment can focus light with a lens to form a small-diameter light spot and irradiate the magnetic element 10, and convert the change in the intensity of the irradiated light into a change in the output voltage from the magnetic element 10. In other words, the photodetector 100 can convert light into an electrical signal.

[0087] Furthermore, electron heating by light irradiation is a very fast phenomenon, and this can be used to rapidly change magnetization. For example, when a short-pulse light (e.g., a laser beam with FWHM: 50 fs) is irradiated onto the magnetic element 10, the heating of electrons, which have a low specific heat, occurs very quickly, and the magnetization M1 of the first ferromagnetic layer 1, which is caused by the electron spin, also changes very quickly. As a result, the rise time of the output voltage from the magnetic element 10 is also fast. On the other hand, after irradiation with short-pulse light, the magnetization of the first ferromagnetic layer 1 returns to its initial state, and the output voltage from the magnetic element 10 also falls to its initial value. However, even after irradiation with short-pulse light ends, if the heat dissipation of the lattice vibration heat from the magnetic element 10 is slow, the return of the magnetization of the first ferromagnetic layer 1 will be slow, and the fall time of the output voltage from the magnetic element 10 will also be long. Therefore, it is necessary to improve the heat dissipation of the magnetic element 10 to shorten the fall time during the photoresponse.

[0088] As described above, the photodetector element 100 of the first embodiment can improve heat dissipation and shorten the fall time during the photoresponse.

[0089] [Examples of application] The photodetector element 100 according to an embodiment of the present invention can be applied to optical sensors such as image sensors in which a plurality of photodetectors are arranged in one or two dimensions. Such optical sensors can be used in information terminal devices such as smartphones, tablets, personal computers, and digital cameras.

[0090] Furthermore, the optical sensing element 100 according to the embodiment of the present invention can be applied, for example, to the photoelectric conversion element of a receiving device in a communication system where multiple transmitting and receiving devices are connected by optical fibers, and the receiving device transmits and receives optical signals such as laser light. The above communication system may be a communication system that performs short- and medium-distance communication, such as within and between data centers, or long-distance communication, such as between cities. The transmitting and receiving device is installed, for example, within a data center.

[0091] Furthermore, the above communication system may be, for example, a communication system that wirelessly transmits and receives optical signals, such as near-infrared light, between mobile terminals such as smartphones and tablets. Alternatively, the above communication system may be, for example, a communication system that wirelessly transmits and receives optical signals, such as near-infrared light, between a mobile terminal and an information processing device such as a personal computer.

[0092] The present invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

[0093] As described above, the present invention has the effect of improving heat dissipation and shortening the fall time during photoresponse, and is useful for photodetectors in general. [Explanation of Symbols]

[0094] 1 First ferromagnetic layer 1a Upper surface of the first ferromagnetic layer 2 Second ferromagnetic layer 2a Lower surface of the second ferromagnetic layer 3 Spacer layer 10 Magnetic elements 11 Upper electrode 12. Lower electrode layer (seed layer) 12a Lower surface of the seed layer 13, 13-1, 13-2 Heatsink Layer 14. Insulating layer 15 Laminate 20, 120 Lower electrode 20a, 120a: Portions in contact with the second ferromagnetic layer 21, 22 Connection area (area) 23 Stenosis 25 Insulator 31, 32 Thermally conductive insulating layer (thermally conductive insulating material) 40 circuit boards 100, 200 photodetectors L light S Light Spot SW width of the constriction

Claims

1. A magnetic element comprising a first ferromagnetic layer irradiated with light, a second ferromagnetic layer, and a spacer layer sandwiched between the first and second ferromagnetic layers, An upper electrode in contact with the first surface of the first ferromagnetic layer opposite to the spacer layer, A lower electrode in contact with the second surface of the second ferromagnetic layer opposite to the spacer layer, A photodetector comprising, The lower electrode has a narrowed planar shape in the region including the portion in contact with the second ferromagnetic layer, and includes a heat sink layer of a thickness that functions as a heat sink. A photodetector in which the entire magnetic element, including the upper electrode, is covered with a thermally conductive insulating material.

2. The photodetector element according to claim 1, wherein the width of the constriction of the lower electrode is smaller than the spot diameter of the irradiated light.

3. The photodetector element according to claim 1, wherein the lower electrode is provided with a substrate on the side opposite to the magnetic element, and a layer containing the same or a different thermally conductive insulating material as the thermally conductive insulating material is provided between the lower electrode and the substrate.

4. The photodetector element according to claim 1, wherein the upper electrode is light-transmitting.

5. The photodetector element according to claim 1, wherein the thickness of the heat sink layer is 100 nm or more and 1000 nm or less.

6. The photodetector element according to claim 1, wherein the thermally conductive insulating material includes either AlN or AlON, or both.

7. The photodetector element according to claim 1, wherein the heat sink layer includes a layer of either Ru or Cu, or a laminated film of Cu and a metal other than Cu.

8. The lower electrode includes a seed layer on the side in contact with the magnetic element and a heat sink layer in contact with the side of the seed layer opposite to the magnetic element. The photodetector element according to claim 1, wherein the seed layer includes a layer of either Ru or Cu, or both, or includes a laminated film of Cu and a metal other than Cu.

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