JP7558496B2 - Optical spin device, information storage device using the same, and method of operating the optical spin device - Google Patents

Description

The present invention relates to an optical spin device, an information storage device using the same, and an operation method of the optical spin device.

As the information society develops, there is a demand for further improvements in memory recording density. Magnetic random access memory (MRAM), which can record information non-volatilely for long periods of time, is expected to be used as the next-generation "universal memory" to replace semiconductor memory. Existing MRAM, which uses electric current to write and read information, has not yet fully established its superiority over semiconductor memory in terms of power consumption, element operating speed, signal delays caused by electrical wiring, etc.

Magnetic memories using Heusler alloy thin films, which are expected to have a larger magnetoresistance effect, have been proposed (see, for example, Patent Document 1). Writing data using the diffusion of electron spins (see, for example, Non-Patent Document 1) and writing to magnetic memories using extremely short light pulses are known (see, for example, Non-Patent Document 2). Imaging of magnetic thin film samples using spin defects in diamond is also known (see, for example, Non-Patent Document 3).

JP 2016-134520 A

J. Puebla1, J. Kim, K. Kondou, Y. Otani "Spintronic devices for energy-efficient data storage and energy harvesting," Communications Materials 1, 1-9 (2020) A. V. Kimel, M. Li "Writing magnetic memory with ultrashort light pulses" Nature Reviews Mater. 4, 189 (2019) David A. Simpson, et al., "Magneto-optical imaging of thin magnetic films using spins in diamond" Scientific Reports 6, P22797 (2016)

Existing MRAMs use electrical signals to write and read information, but there are limitations to reducing power consumption and improving operating speed. They also have low compatibility with optical information technology, which is expected to develop rapidly in the future.

The present invention aims to provide an optical spin device that can store information non-volatilely and operate at high speed with low power consumption, and an information storage device using the same.

In one aspect of the disclosure, the optical spin device comprises:
a magnetic material layer whose magnetization direction changes under the action of light or electricity;
a spin defect layer including defects whose electron spin state can be externally manipulated and whose emission intensity changes in response to a magnetic field;
The emission intensity of the defects varies in response to a magnetic field from the magnetic material layer, and the variation in emission intensity is read out optically or electrically.

The optical spin device of the present invention can retain magnetic information in a non-volatile manner and is capable of high-speed operation with low power consumption. An information retention device using the optical spin device of the present invention is capable of writing and reading information at high speed and with high sensitivity. In a configuration in which at least one of the writing and reading is performed by optical signals, power consumption and wiring delays are significantly reduced, and it has a high affinity with optical information technology.

1 is a diagram showing a basic configuration of an optical spin device according to an embodiment. FIG. 2 is a schematic diagram of an optical spin device according to the first embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a second embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a third embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a fourth embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a fifth embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a sixth embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a seventh embodiment. FIG. 13 is a schematic diagram of an optical spin device according to an eighth embodiment. FIG. 13 is a schematic diagram of an optical spin device according to a ninth embodiment. FIG. 23 is a schematic diagram of an optical spin device according to a tenth embodiment. FIG. 1 is an exploded schematic diagram of an information storage device to which an optical spin device is applied.

In one aspect of the embodiment, information is recorded non-volatilely by utilizing changes in magnetization direction due to interactions between light and spin, such as the inverse Faraday effect and the inverse Cotton-Mouton effect. The recorded information is read out using photoluminescence from defects (hereinafter referred to as "spin defects") that have electronic spin and whose emission intensity changes depending on the direction and magnitude of a magnetic field. Spin defects are a type of lattice defect that causes light absorption and emission. When carriers are excited by spin defects and emit light, the intensity of the photoluminescence changes depending on the direction and magnitude of the magnetic field acting on the spin defects. Information can be read out by detecting the change in emission intensity due to this photoluminescence.

Figure 1 is a basic configuration diagram of an optical spin device 10 according to an embodiment. The optical spin device 10 has a magnetic material layer 15 whose magnetization direction changes due to the action of light or electricity, and a spin defect layer 13 containing spin defects whose emission intensity changes in response to a magnetic field. The state of electron spin in the spin defects (hereinafter referred to as "spin defects") in the spin defect layer 13, or the transition between states that the electron spin can take, can be manipulated externally.

As the spin defect layer 13, a layer of diamond containing nitrogen-vacancy (N-V) complex defects, a layer of silicon carbide (SiC) containing silicon atomic vacancies or nitrogen-vacancy complex defects, a layer of boron nitride (BN) containing boron vacancies, or a layer of a semiconductor or insulator having a band gap similar to these and containing a luminescence center whose electron spin state can be manipulated from the outside and whose luminescence intensity changes in response to a magnetic field can be used.

For example, the electron spin of a negatively charged N-V defect in diamond can take three quantum states, 0, -1, and +1, with a magnetic quantum number _mS . This N-V defect is also called a nitrogen-vacancy (NV) center. An NV center is a complex defect in a diamond crystal in which a carbon atom (C) is replaced with nitrogen (N) and there is a vacancy (V) adjacent to it. The NV center acts as a spin defect whose emission intensity changes depending on the direction and magnitude of the electromagnetic field. This property is not lost even at room temperature, so various applications are conceivable.

In the NV center, the energy difference between the state of m _S =0 and the state of m _S =±1 is 12 μeV. By irradiating microwaves of about 3 GHz, which corresponds to this energy, it is possible to manipulate the state of the electron spin. Note that the irradiation of microwaves that manipulate the state of the electron spin is different from the irradiation of excitation light that causes photoluminescence from spin defects. Photoluminescence is the emission of light (visible light, infrared light, etc.) that occurs when returning from an excited state to the ground state.

The spin defect layer 13 and the magnetic material layer 15 can be laminated on an organic or inorganic substrate 11. For example, the spin defect layer 13 may be formed on a substrate such as glass, silicon, or polyimide, and the magnetic material layer 15 may be formed on the spin defect layer 13. After a synthetic diamond layer, a SiC layer, a BN layer, or the like is formed on the substrate 11, spin defects may be introduced by ion or electron beam irradiation or the like to form the spin defect layer 13. When forming a diamond layer, a diamond thin film may be grown while doping with nitrogen atoms by a chemical vapor deposition (CVD) method using nitrogen gas. In the above method, spin defects are generated over the entire surface (the depth direction can be controlled by adjusting the acceleration energy of ions, etc. and growth parameters), but selective introduction is also possible, such as by processing micron-order grooves by micromachining on a diamond substrate having a specified surface orientation and selectively generating NV centers in the grooves during the growth process.

The direction of magnetization of the magnetic material layer 15 can be changed by either an electrical signal or an optical signal. The direction of magnetization of the magnetic material layer 15 may be perpendicular to the surface or in-plane. Here, the "perpendicular to the surface" direction is the normal direction to the surface of the laminate, and the "in-plane" direction is the direction parallel to the surface of the laminate.

A wide variety of materials can be used for the magnetic material layer 15. When the direction of magnetization is changed by optical input, magnetic materials consisting of two or more kinds of atoms having spins in opposite or nearly opposite directions can be used, i.e., antiferromagnetic materials, ferrimagnetic materials, and tilted antiferromagnetic materials such as GdFeCo alloys, TbFeCo alloys, Bi-substituted yttrium iron garnet (Bi:YIG), and ferrimagnetic Heusler alloys (Mn ₂ CoGa, Mn ₂ PtGa, Mn ₂ RuGa, Mn ₂ FeGa, Mn ₂ CoAl, Mn ₂ VAl). Since ferrimagnetism and tilted antiferromagnetism correspond to special cases of antiferromagnetism (when the magnitude of the magnetic moment of the spin is not completely canceled as a whole), hereinafter, when antiferromagnetism is mentioned, it includes ferrimagnetism and tilted antiferromagnetism. Ferromagnetic materials such as FePt and CoPt can also be used.

Alternatively, a multilayer film or granular thin film containing at least one of an antiferromagnetic material, a ferromagnetic material, and a nonmagnetic material may be used. As the diamagnetic material forming the multilayer film or granular thin film, an IrMn alloy, an FeMn alloy, a CuMnAs alloy, a GdFeCo alloy, a TbFeCo alloy, or the like may be used. As the ferromagnetic material, pure metals such as Fe, Co, Gd, or alloys such as CoFeB, FePt, CoPt, or the like may be used. As the nonmagnetic material, nonmagnetic metals such as Au, Pd, Ru, Pt, or oxides or nitrides such as Al, Mg, Si, or amorphous carbon may be used. When using a multilayer film of a diamagnetic material and a ferromagnetic material, it is preferable to use a ferromagnetic material that is exchange-coupled with the diamagnetic material and exhibits magnetic anisotropy in the same direction. When using a multilayer film made of two or more types of ferromagnetic materials, it is particularly preferable to use a Co/Gd multilayer film in which the magnetization directions of the layers are antiferromagnetically coupled. When using a non-magnetic material, it is particularly preferable to use a non-magnetic material that imparts perpendicular magnetic anisotropy to the magnetic material, such as MgO, Au, or Pt. Perpendicular magnetic anisotropy is the property in which the direction of magnetization is perpendicular to the film surface.

For magnetic recording applications, antiferromagnetic materials or multilayer films with perpendicular magnetic anisotropy are particularly preferred, in which the direction of magnetization changes to parallel or antiparallel to the direction of light propagation depending on the polarization state (clockwise or counterclockwise rotation) when irradiated with elliptically polarized pulsed light. Circularly polarized light is a special case of elliptically polarized light (circularly polarized light is elliptically polarized light with equal amplitudes in each direction), so in the following, when we refer to elliptically polarized light, we include circularly polarized light. Linearly polarized light can also be used.

Antiferromagnetic materials whose magnetization direction changes when irradiated with elliptically polarized or linearly polarized light and whose magnetization direction shows perpendicular magnetic anisotropy include GdFeCo alloy, TbFeCo alloy, Mn ₂ CoGa Heusler alloy, etc. In addition to antiferromagnetic materials, a multilayer film showing perpendicular exchange bias, which is made by stacking a thin film of an antiferromagnetic material and a thin film of a ferromagnetic material showing perpendicular magnetic anisotropy, is also considered to be a promising material that is expected to show magnetization reversal by light irradiation. For example, an antiferromagnetic thin film such as an FeMn alloy or IrMn alloy may be stacked with a ferromagnetic thin film such as an FePt alloy, a CoPt alloy, or a Pt/Co multilayer.

When a thin film of antiferromagnetic material or a multilayer film with antiferromagnetic coupling between layers is used for the magnetic material layer 15, which is created so that the axis of easy magnetization is parallel to the film surface, the direction of magnetization may be reversed by irradiating it with linearly polarized pulsed light.

When the magnetization direction of the magnetic material layer 15 is changed by an electrical input, a material whose magnetization direction changes with current or voltage is used. As the material whose magnetization direction changes with current, a multilayer film of a ferromagnetic material (Fe, Co, CoFeB, MnGa, etc.) or an antiferromagnetic material (YIG, etc.) and a conductive nonmagnetic material may be used. As the conductive nonmagnetic material, a heavy metal such as Pt, a topological insulator such _{as Bi2Se3} , a transition metal chalcogenide such as _WTe2, etc. can be used.

A material whose magnetization direction changes with voltage can be a multilayer film of a ferromagnetic material and an insulating non-magnetic material. In addition to pure metals such as Fe, alloys such as CoFeB and CoFe can be used as ferromagnetic materials for the multilayer film. MgO can be used as an insulating non-magnetic material.

Other layers may be present between the substrate 11 and the spin defect layer 13, or between the spin defect layer 13 and the magnetic material layer 15, as long as they do not interfere with the action of the magnetic field from the magnetic material layer 15 to the spin defect layer 13 and the light emission of the spin defect layer.

As described above, the spin defect layer 13 can read out minute magnetization changes with high sensitivity by sensing the change in emission intensity according to the magnetic field of the spin defects. As a mechanism for reading out the emission intensity from the spin defect layer 13, an optical detection layer, an optical wiring layer, etc. may be incorporated within the stack, as described below, or may be provided outside the stack. The optical spin device 10 is a device with extremely low power consumption that operates based on a different concept from existing MRAMs. Compared to existing MRAMs that read out magnetic information using an electric current, it is possible to significantly reduce power consumption during reading.

When writing information using the interaction between light and electron spin, power consumption during writing is significantly reduced compared to existing MRAMs that use electric current to write, and the writing speed limit of MRAMs can be exceeded. In addition, high-speed magnetization reversal is possible like with antiferromagnets, but materials that only show minute magnetization, or insulating materials that do not conduct electricity, can also be used for the magnetic material layer 15, expanding the freedom of material selection.

First Example
2 is a schematic diagram of an optical spin device 10A of Example 1. In the optical spin device 10A, information is written by an optical signal L _IN and information is read by an optical signal L _OUT .

The optical spin device 10A has a magnetic material layer 15A, a spin defect layer 13, and an optical wiring layer 21 on a substrate 11. In this example, the magnetic material layer 15A has perpendicular magnetic anisotropy, and the magnetization direction is perpendicular to the substrate surface. The magnetic material layer 15A is made of an antiferromagnetic material such as a GdFeCo alloy, a TbFeCo alloy, or a _Mn2CoGa Heusler alloy.

When the magnetic material layer 15A is irradiated with an optical signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15A is reversed in the irradiated area (operation (2)). This magnetization reversal is due to the interaction between the light and the electron spins (and the magnetization as a collection of electron spins). The magnetization direction changed by the action of the light is maintained in a non-volatile manner at room temperature.

When reading out the magnetization direction of the magnetic material layer 15A, the spin defect layer 13 is irradiated with the excitation light L _PUMP emitted from the excitation light source 17 (operation (3)). In the example of FIG. 2, the excitation light L _PUMP is irradiated from above the magnetic material layer, but it may be irradiated from the side of the stack or from the side of the substrate 11. Also, instead of using an external light source, a light emitting layer or light emitting element for excitation may be stacked on the magnetic material layer 15. As described later, the irradiation configuration of the excitation light can be appropriately designed depending on the order, arrangement, materials, etc. of the stack. As the excitation light source 17, a laser diode (LD), a light emitting element (LED), etc. may be used.

Irradiation of the excitation light L _PUMP is usually performed under irradiation of electromagnetic waves, but irradiation of electromagnetic waves is not essential. In general, in a state where the state of electron spin is manipulated by irradiation with electromagnetic waves of a resonant frequency (hereinafter referred to as "resonant electromagnetic waves"), the magnetic field is detected by utilizing the change in the emission intensity of spin defects caused by irradiation with excitation light from the emission intensity in non-resonance. Since the resonant electromagnetic waves react and change very sensitively to the magnetic field, the magnetic field strength can be obtained with high sensitivity. When reading memory information (for example, binary values of "0" and "1"), the resonant frequency is set to the higher magnetic field strength (for example, this is defined as "1"), and the increase or decrease in the emission intensity between the 0/1 state may be detected.

On the other hand, it is also possible to read out 0/1 without irradiating electromagnetic waves by utilizing the quenching phenomenon at a specific magnetic field strength called level anti-crossing. In this case, the magnetic field strength of the "0" or "1" state must be set to a specific strength at which the quenching phenomenon occurs. In other words, reading out magnetic field information by irradiating excitation light can be done by reading out the change in emission intensity according to the magnetic field while irradiating resonant electromagnetic waves, or by using the level anti-crossing phenomenon to read out the change in emission intensity without resonant electromagnetic waves.

To explain in more detail about resonant electromagnetic wave irradiation and level anti-crossing, when a spin defect is irradiated with electromagnetic waves equal to the energy difference between spin sublevels (between 0 and ±1 in the case of diamond NV, and between ±1/2 and ±3/2 in the case of silicon vacancies in silicon carbide), that is, resonant electromagnetic waves, the spin state changes. This is called manipulation. When excitation light is irradiated in this state, the emission intensity increases or decreases (this depends on the defect type) compared to when there is no resonant electromagnetic wave irradiation. When a magnetic field is applied, the energy difference between the sublevels increases by the amount of Zeeman splitting. If a resonant electromagnetic wave corresponding to the increase in the energy difference is irradiated, the increase or decrease in the emission intensity can be confirmed, and the magnetic field strength (the magnetic field vector (direction) can also be determined by advanced measurements) can be obtained from the frequency of the resonant electromagnetic wave.

When using the optical spin device 10 of the embodiment to operate as a memory, it is sufficient to know the presence or absence of a magnetic field and its magnitude (direction is not detected), so the frequency is fixed (i.e., not swept) according to the magnetic field strength of the "0" or "1" state (this is determined by design), and resonance/non-resonance is defined as 0/1. This detection method can be further advanced to use a phenomenon called level anti-crossing, that is, the phenomenon in which light is quenched where the spin sublevels separated by Zeeman splitting cross (the magnetic field is adjusted to the strength at which crossing occurs), making it possible to determine 0/1. This method does not require electromagnetic waves, so power consumption can be further reduced. In the embodiment, the change in the emission of the spin defect layer 13 may be detected under irradiation of electromagnetic waves, or the change in the emission intensity may be read without irradiation of electromagnetic waves.

After being excited by the excitation light L _PUMP , the electrons trapped in the spin defects transition quickly (on the order of 10 nanoseconds) to the ground state and emit light (operation (4)). The emission intensity at this time varies depending on the direction and magnitude of the magnetic field acting on the excitation position of the spin defect layer 13 (during resonance). In the configuration of FIG. 2, the wavelengths of the write optical signal L _IN , the excitation light L _PUMP , and the photoluminescence wavelength from the spin defects are selected so that their functions, i.e., changing the magnetization direction and detecting magnetic field changes, do not interfere with each other.

The light emitted from the spin defect layer 13 is output as an optical signal L _OUT from the optical wiring layer 21 (operation (5)). The optical wiring layer 21 may have any configuration that can extract the light emitted from the spin defects to the outside. An optical signal may be extracted using a photonic crystal waveguide, or a combination of a diffraction grating or a micromirror and a silicon waveguide may be used. Also, an optical fiber may be used for at least a part of the optical wiring.

The stacking order of the optical spin device 10A is not limited to the example in FIG. 2. An optical wiring layer 21 may be placed between the spin defect layer 13 and the magnetic material layer 15A as long as it does not impede the action of the magnetic field from the magnetic material layer 15A to the spin defect layer 13. In this case, excitation light and electromagnetic waves for reading may be irradiated onto the spin defect layer 13 from the substrate 11 side. The configuration in FIG. 2 has almost no wiring delay, consumes very little power, and realizes high-speed, high-sensitivity writing and reading.

Second Example
3 is a schematic diagram of an optical spin device 10B of the second embodiment. The optical spin device 10B has a magnetic material layer 15B, a spin defect layer 13, and an optical wiring layer 21 on a substrate 11. As in FIG. 2, the optical spin device 10B writes information using an optical signal L _IN and reads information using an optical signal L _OUT .

The magnetic material layer 15B has an easy axis of magnetization parallel to the film surface. The magnetic material layer 15B is formed, for example, of a thin film of a ferromagnetic material. Magnetic information is written in the magnetic material layer 15B using linearly polarized light. When the magnetic material layer 15B is irradiated with a linearly polarized optical signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15B changes within the plane in the irradiated area (operation (2)). The magnetization direction changed by the action of light is maintained in a non-volatile manner at room temperature.

When reading out magnetic information from the magnetic material layer 15B, the spin defect layer 13 is irradiated with excitation light L _PUMP from the excitation light source 17 (operation (3)). As described above, the excitation light may be irradiated in a state in which the state of the electron spin is manipulated by irradiating electromagnetic waves that are matched to the resonance frequency of the higher magnetic field strength. Alternatively, the excitation light may be irradiated without irradiating the resonant electromagnetic wave by utilizing the level anti-crossing phenomenon. Light emission is obtained from the spin defects by irradiating the excitation light (operation (4)). The intensity of the light emission at this time changes depending on the direction and magnitude of the magnetic field acting on the spin defect layer 13. The light emission from the spin defect layer 13 is output as an optical signal L _OUT from the optical wiring layer 21 (operation (5)).

The configuration in Figure 3 also has almost no wiring delay, consumes very little power, and achieves high-speed, highly sensitive writing and reading.

<Third Example>
4 is a schematic diagram of an optical spin device 10C of a third embodiment. The optical spin device 10C writes magnetic information by an optical signal L _IN and reads the magnetic information by an electrical signal I _OUT . The optical spin device 10C has a magnetic material layer 15, a spin defect layer 13, and a photodetection layer 22 on a substrate 11. The magnetic material layer 15 may be a magnetic material layer 15A having perpendicular magnetic anisotropy, or a magnetic material layer 15B having an easy axis of magnetization in the plane.

When the magnetic material layer 15 is irradiated with the optical signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15 changes in the irradiated area (operation (2)). Depending on the material used in the magnetic material layer 15 and the direction of the easy axis of magnetization, elliptically polarized or linearly polarized light is made incident.

When reading out the magnetization direction of the magnetic material layer 15, the spin defect layer 13 is irradiated with excitation light L _PUMP from the excitation light source 17 (operation (3)). The irradiation of the excitation light causes light emission by photoluminescence from the spin defects (operation (4)). The light emission intensity varies depending on the direction and magnitude of the magnetic field acting on the spin defect layer 13. The light emitted from the spin defect layer 13 is received by the photodetection layer 22, and a photocurrent is output as an electrical signal I _OUT (operation (5)).

The light detection layer 22 may be a general photodiode using a pn junction, or an avalanche photodiode (APD) with high light receiving sensitivity and S/N ratio. The light detection layer 22 is preferably capable of detecting weak light with a low bias, and the material, composition, configuration, etc. are selected according to the wavelength of the light emitted from the spin defects. When detecting weak visible light or near-infrared light, for example, a Si/InGaAs PIN photodiode may be used.

The magnetic information held by the magnetic material layer 15 is read out as a change in the emission intensity of the spin defect layer 13, i.e., a change in the current value of the photocurrent or the number of light pulses. The photocurrent may be converted into a voltage value by a transimpedance amplifier.

In the configuration of Fig. 4, writing is performed by optical signals, the power consumption during writing is significantly reduced, and the writing speed is improved. As in the first and second embodiments, the order of layers on the substrate 11 and the direction of irradiation of the excitation light L _PUMP are not limited to the example of Fig. 4. The order of layers and the position of the excitation light source 17 may be changed as long as the function of each layer is not hindered.

<Fourth Example>
5 is a schematic diagram of an optical spin device 10D of Example 4. The optical spin device 10D writes magnetic information by an electric signal E _IN and reads out the magnetic information by an optical signal L _OUT .

The optical spin device 10D has a magnetic material layer 15, a write electrode layer 24, a spin defect layer 13, and an optical wiring layer 21 on a substrate 11. The magnetic material layer 15 may be a magnetic material layer 15A having perpendicular magnetic anisotropy, or a magnetic material layer 15B having an easy axis of magnetization in the plane.

By applying a current or a voltage as an electric signal E _IN to the write electrode layer 24 (operation (1)), the direction of magnetization in the magnetic material layer 15 changes, and magnetic information is written (operation (2)).
When a current is applied as the electric signal E _IN , a spin torque (including a spin transfer torque and a spin orbit torque) acts on the magnetic material layer 15 from the write electrode layer 24, changing the direction of magnetization. When a voltage is applied, the direction of magnetization is changed by utilizing a change in the magnetic anisotropy of the magnetic material layer 15 caused by the voltage application. It is desirable that the write electrode layer 24 is formed thin enough that the spin defect layer 13 can detect a change in the magnetic field from the magnetic material layer 15.

When reading out the magnetization direction of the magnetic material layer 15, the spin defect layer 13 is irradiated with the excitation light L _PUMP from the excitation light source 17 under irradiation of a resonant electromagnetic wave (operation (3)). In Fig. 5, the excitation light L _PUMP is irradiated from the magnetic material layer 15 side, but the excitation light L _PUMP may be irradiated from the substrate 11 side. In this case, the write electrode layer 24 functions as a reflective film and can prevent malfunction of the magnetic material layer 15 due to the excitation light L _PUMP .

Irradiation with the excitation light L _PUMP causes light emission from the spin defect layer 13 (operation (4)). The intensity of light emission by photoluminescence varies depending on the direction and magnitude of the magnetic field acting on the spin defect layer 13. The light emitted from the spin defect layer 13 is output as an optical signal L _OUT from the optical wiring layer 21 (operation (5)).

In the configuration of Fig. 5, the power consumption and wiring delay during readout are close to zero, and high-speed, high-sensitivity readout is realized. As in the first to third embodiments, the order of layers on the substrate 11 and the direction of irradiation of the excitation light L _PUMP are not limited to the example in Fig. 5. The order of layers and the position of the excitation light source 17 may be changed as long as the function of each layer is not hindered.

Fifth Example
6 is a schematic diagram of an optical spin device 10E of Example 5. The optical spin device 10E writes magnetic information using an electric signal _EIN and reads out magnetic information using an electric signal _IOUT .

The optical spin device 10E has a magnetic material layer 15, a write electrode layer 24, a spin defect layer 13, and a light detection layer 22 on a substrate 11. The magnetic material layer 15 may be a magnetic material layer 15A having perpendicular magnetic anisotropy, or a magnetic material layer 15B having an easy axis of magnetization in the plane.

By applying a current or voltage to the write electrode layer 24 as an electric signal E _IN (operation (1)), the direction of magnetization of the magnetic material layer 15 changes, and magnetic information is written (operation (2)). When reading out magnetic information from the magnetic material layer 15, the spin defect layer 13 is irradiated with excitation light L _PUMP from the excitation light source 17 under irradiation with a resonant electromagnetic wave (operation (3)). As described above, the excitation light L _PUMP may be irradiated from the substrate 11 side. Irradiation with the excitation light L _PUMP produces light emission from the spin defects (operation (4)). The light emission from the spin defect layer 13 is received by the photodetection layer 22, and a photocurrent is output as an electric signal I _OUT (operation (5)).

In the configuration of FIG. 6, both writing and reading are performed by electric signals, but unlike existing MRAMs, magnetic information is read by utilizing the change in the emission intensity of spin defects according to the magnetic field generated by the magnetic material layer, so that the sensing sensitivity of magnetic information is greatly improved. In existing MRAMs that use the magnetoresistance effect to read magnetic information, the material of the magnetic material layer is limited to some that exhibit a significant magnetoresistance effect (e.g., Fe/MgO tunnel junction), but in this element that detects a magnetic field and reads magnetic information, various materials can be used, such as antiferromagnetic materials that can reverse magnetization at high speed and with low power consumption, and insulating magnetic materials that do not conduct electricity (e.g., Bi:YIG). The order of stacking on the substrate 11 and the irradiation direction of the excitation light L _PUMP are not limited to the example in FIG. 6, as in the first to fourth embodiments. The order of stacking and the position of the excitation light source 17 may be changed as long as the function of each layer is not hindered.

Sixth Example
7 is a schematic diagram of an optical spin device 10F of the sixth embodiment. The optical spin device 10F has a magnetic material layer 15, a spin defect layer 13, and an optical wiring layer 21 on a substrate 11. The magnetic material layer 15 includes a fixed layer 151 whose magnetization direction is fixed, a free layer 152 whose magnetization direction is reversible, and a spacer layer 153 disposed between the fixed layer 151 and the free layer 152.

The fixed layer 151 may be made of a ferromagnetic material such as CoFeB, FePt, or CoPt, and the free layer 152 may be made of an antiferromagnetic material such as GdGeCo, TbFeCo, or Mn ₂ CoGa. The spacer layer 153 may be made of a nonmagnetic material.

When the magnetic material layer 15 is irradiated with an optical signal L _IN (operation (1)), the magnetization direction of the free layer 152 changes in the irradiated area (operation (2)). Depending on the material used in the magnetic material layer 15 and the direction of the easy axis of magnetization, elliptically polarized or linearly polarized light is incident.

When reading out the magnetization direction of the magnetic material layer 15, the spin defect layer 13 is irradiated with the excitation light L _PUMP from the excitation light source 17 under irradiation of the resonant electromagnetic wave (operation (3)). As described above, the excitation light L _PUMP may be irradiated from the substrate 11 side. The irradiation of the excitation light L _PUMP produces light emission from the spin defects (operation (4)). The light emission from the spin defect layer 13 is output as an optical signal L _OUT by the optical wiring layer 21 (operation (5)).

In the configuration of FIG. 7, when the magnetization directions of the fixed layer 151 and the free layer 152 are the same, the sum of the magnetic fields of the two layers (corresponding to a logical value of "1") is read out. When the magnetization directions of the fixed layer 151 and the free layer 152 are opposite, the difference between the two magnetic fields (corresponding to a logical value of "0") is read out. By detecting the sum and difference of the magnetic fields acting on the spin defect layer 13, the read sensitivity is improved.

In the configuration example of FIG. 7, magnetic information is written by the optical signal L _IN and read by the optical signal L _OUT , but either writing or reading may be performed by an electric signal. Depending on whether light or electricity is applied to the magnetic material layer 15, the layer structure of the magnetic material layer 15 and the material of each layer are appropriately selected. The arrangement of the fixed layer 151 and the free layer 152 is not limited to the arrangement in the stacking direction, and they may be arranged on the same plane. By arranging the fixed layer 151 and the free layer 152 of the same area in one section and detecting the direction of magnetization as a change in light emission intensity with the spin defect layer 13, the difference and sum of the magnetic fields of the fixed layer 151 and the free layer 152, that is, the information "0" and "1", can be read.

Seventh Example
8 is a schematic diagram of an optical spin device 10G of the seventh embodiment. The optical spin device 10G has a magnetic material layer 15A, a spin defect layer 13, and an optical wiring layer 21 on a substrate 11. The magnetic material layer 15A and the spin defect layer 13 are arranged in the same plane with a predetermined distance between them.

8, a magnetic material layer 15A having perpendicular magnetic anisotropy and a spin defect layer 13 are disposed on an optical wiring layer 21 with an air layer 18 sandwiched therebetween. The air layer 18 is an example of a spacer layer. The width of the air layer 18, i.e., the distance between the magnetic material layer 15A and the spin defect layer 13, is a distance at which the magnetic field of the magnetic material layer 15A can act on the spin defect layer 13. The magnetic material layer 15A can be formed of an antiferromagnetic material such as a GdFeCo alloy, a TbFeCo alloy, or a _Mn2CoGa Heusler alloy.

When the magnetic material layer 15A is irradiated with an elliptically polarized optical signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15A is reversed in the irradiated area (operation (2)). When reading out the magnetization direction of the magnetic material layer 15A, the spin defect layer 13 is irradiated with excitation light L _PUMP from an excitation light source (operation (3)). In the arrangement configuration of Fig. 8, the optical signal L _IN for writing and the excitation light L _PUMP may be light of the same wavelength λ1 depending on the emission wavelength of the spin defects.

The spin defect layer 13 is excited by the excitation light L _PUMP and emits light by photoluminescence (operation (4)). The light emitted from the spin defect layer 13 is outputted from the optical wiring layer 21 as an optical signal L _OUT (operation (5)).

The configuration of FIG. 8 is useful when the magnetic material layer 15 is opaque due to its material or thickness. It is also advantageous in that the same wavelength of light can be used for writing and reading. As with FIG. 2, power consumption and wiring delays can be minimized for both writing and reading.

Eighth Example
9 is a schematic diagram of an optical spin device 10H of the eighth embodiment. The optical spin device 10H has a magnetic material layer 15B, a spin defect layer 13, and an optical wiring layer 21 on a substrate 11. The magnetic material layer 15B and the spin defect layer 13 are arranged in the same plane with a magnetically permeable layer 19 sandwiched therebetween. The magnetically permeable layer 19 is an example of a spacer layer. The magnetically permeable layer 19 is made of a high magnetic permeability material such as permalloy or ferrite, and functions as a yoke that concentrates magnetic lines of force on the spin defect layer 13, thereby improving the detection sensitivity of the magnetization of the magnetic material layer 15B by the spin defect layer 13. The magnetic material layer 15B has an easy magnetization axis in the in-plane direction, and the magnetic field generated by the magnetic material layer 15B acts on the spin defect layer 13 via the magnetically permeable layer 19.

When the magnetic material layer 15B is irradiated with a linearly polarized optical signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15B changes in the irradiated area (operation (2)). When reading out the magnetization direction of the magnetic material layer 15B, the spin defect layer 13 is irradiated with excitation light L _PUMP from an excitation light source (operation (3)). In the arrangement configuration of Figure 9, depending on the emission wavelength of the spin defects, the write optical signal L _IN and the excitation light L _PUMP may be light of the same wavelength λ1.

The spin defect layer 13 is excited by the excitation light L _PUMP and emits light by photoluminescence (operation (4)). The light emitted from the spin defect layer 13 is outputted from the optical wiring layer 21 as an optical signal L _OUT (operation (5)).

The configuration of FIG. 9 is also useful when the magnetic material layer 15 is opaque due to its material or thickness. It is also advantageous in that the same wavelength of light can be used for writing and reading. As with FIG. 3, it is possible to minimize power consumption and wiring delays for both writing and reading.

Ninth Example
10 is a schematic diagram of an optical spin device 10I of the ninth embodiment. The optical spin device 10I has a magnetic material layer 15A with perpendicular magnetic anisotropy, a spin defect layer 13, a magnetic permeable layer 29, and an optical wiring layer 21 on a substrate 11. The magnetic material layer 15A and the spin defect layer 13 are arranged in the same plane on the magnetic permeable layer 29 with an air layer 18 sandwiched therebetween. The air layer 18 serves as a spacer layer to separate the magnetic material layer 15A and the spin defect layer 13.

The magnetically permeable layer 29 functions as a yoke and improves the detection sensitivity of the spin defect layer 13. The magnetically permeable layer 29 is transparent to the extent that it does not interfere with the output of light emitted from the spin defect layer 13 to the optical wiring layer 21, or has a portion that transmits light. The position of the magnetically permeable layer 29 is not limited to the lower layer of the spin defect layer 13 and the magnetic material layer 15A, and may be disposed in at least one of the lower layer and the upper layer of the spin defect layer 13 and the magnetic material layer 15A. When the magnetically permeable layer 29 is provided in the lower layer and the upper layer of the spin defect layer 13 and the magnetic material layer 15A, the effect of concentrating the magnetic field lines is enhanced, and the detection sensitivity of the spin defect layer 13 is improved. In addition, when the magnetically permeable layer 29 is provided above the spin defect layer 13 and the magnetic material layer 15A, the magnetically permeable layer 29 is transparent to the writing light and the excitation light to the extent that it does not interfere with writing to the magnetic material layer 15A and reading by the spin defect layer 13, or has a region that transmits light.

When the magnetic material layer 15A is irradiated with an elliptically polarized light signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15A is reversed in the irradiated area (operation (2)). The magnetic field emitted from the magnetic material layer 15A acts on the spin defect layer 13 through the magnetic permeable layer 29. In a perpendicular magnetization film, the magnetic field lines enter and exit the magnetic material layer 15A in the vertical direction (direction perpendicular to the surface), and act on the spin defect layer 13 through the space above and below the magnetic material layer 15A. As shown in FIG. 10, the magnetic permeable layer 29 allows the magnetic field lines spreading into the air to be collected in the magnetic permeable layer 29, so that the magnetic field acting on the spin defect layer 13 becomes stronger. When reading out magnetic information from the magnetic material layer 15A, the spin defect layer 13 is irradiated with excitation light L _PUMP from an excitation light source (operation (3)). In the arrangement of FIG. 10, depending on the emission wavelength of the spin defect, the writing optical signal L _IN and the pump light L _PUMP may be light of the same wavelength λ1.

The spin defect layer 13 is excited by the excitation light L _PUMP and emits light by photoluminescence (operation (4)). The light emitted from the spin defect layer 13 is outputted from the optical wiring layer 21 as an optical signal L _OUT (operation (5)).

The configuration of FIG. 10 is advantageous in that it improves the detection sensitivity of the spin defect layer 13 and suppresses leakage of magnetic field lines from the magnetic material layer. It is similar to FIG. 8 in that it is possible to use light of the same wavelength for writing and reading, and that it is possible to minimize power consumption and wiring delays for both writing and reading.

Tenth Example
11 is a schematic diagram of an optical spin device 10J of Example 10. The optical spin device 10J has, on a substrate 11, a magnetic material layer 15B having an easy axis of magnetization in the horizontal direction, a spin defect layer 13, a magnetic permeable layer 19, and an optical wiring layer 21.

The spin defect layer 13 is surrounded by a magnetically permeable layer 19, and the spin defect layer 13 and the magnetic material layer 15B are arranged in the same plane with the magnetically permeable layer 19 sandwiched between them. The magnetically permeable layer 19 functions as a spacer layer and also as a yoke, improving the detection sensitivity of the spin defect layer 13.

When the magnetic material layer 15B is irradiated with a linearly polarized optical signal L _IN (operation (1)), the magnetization direction of the magnetic material layer 15B changes in the irradiated area (operation (2)). The magnetic field emitted from the magnetic material layer 15B acts on the spin defect layer 13 via the magnetically permeable layer 19. When reading information from the magnetic material layer 15B, the spin defect layer 13 is irradiated with excitation light L _PUMP from an excitation light source under irradiation with a resonant electromagnetic wave (operation (3)). In the arrangement configuration of FIG. 11, depending on the emission wavelength of the spin defect, the optical signal L _IN for writing and the excitation light L _PUMP may be light of the same wavelength λ1.

The spin defect layer 13 is excited by the excitation light L _PUMP and emits light by photoluminescence (operation (4)). The light emitted from the spin defect layer 13 is outputted from the optical wiring layer 21 as an optical signal L _OUT (operation (5)).

The configuration of FIG. 11 is advantageous in that it improves the detection sensitivity of the spin defect layer 13 and suppresses leakage of magnetic field lines from the unit cell. It is similar to FIG. 9 in that it is possible to use light of the same wavelength for writing and reading, and that it is possible to minimize power consumption and wiring delays for both writing and reading.

<Application to information storage devices>
The optical spin device 10 of the embodiment (including optical spin devices 10A to 10J of Examples 1 to 10) is a microscopic element with ultra-high speed, high sensitivity, and low power consumption, and is therefore expected to be applied to information storage and processing devices such as magnetic memories, logic devices, quantum computing, and neuromorphic computing.

12 is a schematic diagram of an information holding device 100 to which the optical spin device 10 of the embodiment is applied. In the example of FIG. 12, the information holding device 100 is based on the configuration of the first to sixth examples in which the magnetic material layer 15 and the spin defect layer 13 are arranged in the stacking direction, and has an information recording layer L1, an information detection layer L2, and an information readout layer L3. In this example, the magnetic material layer 15 with perpendicular magnetic anisotropy including the stacking of the fixed layer 151 and the free layer 152 in FIG. 7 is used as the information recording layer L1. The white area in the figure is an area in which the magnetization directions of the fixed layer 151 and the free layer 152 are opposite (indicated by the reverse arrow in the figure) and information "0" is recorded. The gray area is an area in which the magnetization directions of the fixed layer 151 and the free layer 152 are the same (indicated by the thick upward arrow in the figure) and information "1" is recorded.

The magnetic material layer 15 of the optical spin device 10 is used as an information recording layer L1, and information is written by a write signal SIG. The write signal SIG may be an optical signal or an electrical signal. When information is written by applying a current or voltage, the information recording layer L1 may include a write electrode layer.

The spin defect layer 13 of the optical spin device 10 is used as the information detection layer L2. The optical wiring layer 21 or the optical detection layer 22 of the optical spin device 10 is used as the information readout layer L3. In the example of FIG. 12, the optical detection layer 22 including the photodiode 111 and wiring 112 is used as the information readout layer L3.

The information recording layer L1 of the information holding device 100 has a large number of recording cells 311, and information can be written and read independently for each recording cell 311. To achieve this, the magnetic material layer 15 is patterned into a large number of recording cells 311. For convenience of illustration, only 3×2 recording cells 311 are drawn, but in reality, a large number of cells are arranged in a matrix. The area of one recording cell 311 is minute, and may be, for example, about the beam diameter of the optical signal L _IN for writing. By scanning the writing signal SIG relatively to the recording cells 311, an information value can be written individually to each recording cell 31.

The information written in each recording cell 31 is detected by the information detection layer L2 by irradiating the spin defect layer 13 at a position corresponding to the recording cell 311 to be read with excitation light L _PUMP under irradiation of electromagnetic waves (electromagnetic waves are not shown) or without irradiation of electromagnetic waves. A change in the intensity of the light emitted from the excited spin defect layer 13 represents the magnitude of the magnetic field of the corresponding recording cell 311.

The spin defect layer 13 is, for example, a diamond layer including N-V centers 131. The spin defect layer 13 has N-V centers in grooves formed corresponding to the columns or rows of the recording cells 311 of the information recording layer L1.

The light emitted from the N-V center is detected by the photodiode 111 in the light detection layer 22 constituting the information readout layer L3, and a photocurrent that correlates with the intensity of the incident light is output from the wiring 112. The wiring 112 is formed on the substrate 11 using any conductive material, and can be formed from a highly doped semiconductor, a good conductor of metal, or the like.

The information storage device 100 combines the writing of magnetic information using the interaction between light or electricity and spin, and the reading of magnetic information based on ultra-sensitive magnetic field sensing using spin defects, achieving power savings and speeds that far exceed those of existing non-volatile memories. The information storage device 100 can be applied to optical information technology, which is difficult with existing MRAM, and to technologies that combine electronic and optical information. It can also be applied to non-volatile ultra-high-speed buffer memories that convert electrical signals and optical signals between optical wiring and electronic wiring, and ultra-low power consumption memories that record information from various sensors in the environment and output it to optical wiring, realizing device configurations that are in line with the development of IoT.

The information retention device 100 is capable of writing at speeds of 1 nanosecond or less, which is extremely fast compared to existing memories such as MRAM. The information retention device 100 operates at femtojoules (fJ/b) per bit, consuming significantly less power than existing non-volatile memories.

The optical spin device and information holding device of the embodiment have been described above based on a specific configuration example, but the present invention is not limited to the above-mentioned configuration example, and various modifications or substitutions are possible. For example, in a configuration in which the magnetic material layer 15 and the spin defect layer 13 are arranged in the same plane, a non-magnetic layer such as MgO may be used instead of the air layer and the magnetically permeable layer. The configurations of the first to tenth examples can be combined with each other, and writing or reading of the in-plane arrangement type optical spin devices 10G to 10J may be performed by an electric signal. When the information recording layer L1 is formed by combining a fixed layer and a free layer, the fixed layer and the free layer may be arranged in the in-plane direction within one recording cell 311. The irradiation direction of the excitation light L _PUMP is not limited to irradiation from above the stack, and irradiation may be performed in the lateral direction of the stack or from the substrate 11 side depending on the layer structure.

The configuration of the in-plane arrangement type optical spin devices 10G to 10J may be applied to the information holding device 100, and the information recording layer L1 and the information detection layer L2 may be provided in the same plane for each cell. A control circuit that sequentially selects and controls the information write position and read position may be connected to the information holding device 100. The control circuit may control the relative positions of the write optical signal L _IN and the excitation light L _PUMP with respect to the information recording layer L1 in synchronization with the writing and reading of information for each recording cell 311.

The operating method of the optical spin device is to combine a magnetic material layer with a spin defect layer that contains defects whose electron spin state can be manipulated externally and whose light emission intensity changes in response to a magnetic field, input an optical or electrical signal to the magnetic material layer to change the direction of magnetization, excite the spin defect layer to cause light emission from the defects, and electrically or optically read out the magnetization direction of the magnetic material layer from the light emission. The optical spin device may employ any configuration that achieves such an operation.

10, 10A to 10J Optical spin device 11 Substrate 13 Spin defect layer 15 Magnetic material layer 151 Fixed layer 152 Free layer 153 Spacer layer 17 Excitation light source 18 Air layer (spacer layer)
19, 29 Magnetically permeable layer (spacer layer)
21 Optical wiring layer 22 Light detection layer 24 Electrode layer 100 Information storage device 111 Photodiode 112 Wiring 131 NV center 311 Recording cell L1 Information recording layer L2 Information detection layer L3 Information reading layer

Claims (12)

a magnetic material layer whose magnetization direction changes under the action of light or electricity;
a spin defect layer including defects whose electron spin state can be externally manipulated and whose emission intensity changes in response to a magnetic field;
an emission intensity of the defect varies in response to a magnetic field from the magnetic material layer;
The change in the emission intensity is read out optically or electrically.
Optical spin device. a read mechanism for reading the direction of magnetization of the magnetic material layer based on a change in the emission intensity of the spin defect layer;
The optical spin device of claim 1 further comprising: the readout mechanism is an optical interconnection layer that extracts light emitted in the spin defect layer or a light detection layer that detects the light emission and outputs a photocurrent;
The optical spin device according to claim 2 . The optical spin device according to any one of claims 1 to 3, further comprising an excitation light source that irradiates the spin defect layer with excitation light. The magnetic material layer and the spin defect layer are laminated in a direction perpendicular to the surface.
5. An optical spin device according to claim 1. The magnetic material layer and the spin defect layer are arranged in an in-plane direction.
5. An optical spin device according to claim 1. The optical spin device of claim 6, which has an air layer, a non-magnetic layer, or a magnetically permeable layer as a spacer layer disposed between the magnetic material layer and the spin defect layer. the magnetic material layer includes a multilayer film of a thin film of a diamagnetic material whose magnetization direction changes depending on the polarization state of the light, and a thin film of a ferromagnetic material that exhibits magnetic anisotropy in the same direction as the diamagnetic material;
8. An optical spin device according to claim 1. The magnetic material layer includes a ferromagnetic material layer in which the direction of magnetization changes upon application of a current or a voltage, a multilayer film of a thin film of an antiferromagnetic material and a thin film of a conductive nonmagnetic material, or a multilayer film of a thin film of an antiferromagnetic material and a thin film of an insulating nonmagnetic material.
8. An optical spin device according to claim 1. The optical spin device according to any one of claims 1 to 9 , wherein the spin defect layer has a band gap equal to or larger than the band gap of a silicon carbide layer containing silicon vacancies or nitrogen-vacancy complex defects, and includes a semiconductor or insulator layer containing luminescence centers whose electron spin state can be manipulated externally and whose luminescence intensity changes in response to a magnetic field. In a data storage device using the optical spin device according to any one of claims 1 to 10,
Information is recorded in the magnetic material layer;
The spin defect layer is excited and the information is read out optically or electrically.
Information holding device. A magnetic material layer is combined with a spin defect layer that has defects in which the state of electron spin can be externally manipulated and the emission intensity changes in response to a magnetic field;
inputting an optical signal or an electrical signal to the magnetic material layer to change the direction of magnetization;
exciting the spin defect layer to cause the defects to emit light;
A method of operating an optical spin device, comprising electrically or optically reading out the direction of magnetization of the magnetic material layer from the optical emission.

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