Spin wave excitation detection structure

Abstract

To provide a spin wave excitation detection structure that has a high strength structure, a high spin wave intensity that can be excited, and a wide frequency bandwidth of the spin wave that can be excited.SOLUTION: A spin wave excitation detection structure that excites and detects spin waves includes a support substrate, a conductive film provided on the support substrate, an insulating magnetic film provided on the conductor film, and a conductor wire provided on the insulating magnetic film.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a spin wave excitation detection structure.

Background Art

[0002] With the recent explosive increase in the amount of information handled on the Internet and the like, the speed of CPUs, the speed of medium- and long-distance communication by RF (radio frequency) and optical communication, the increase in data storage capacity, and the miniaturization of each component have been rapidly developing. However, the bottlenecks in improving the processing speed are (1) the heat generation problem due to the physical limit of performance improvement by miniaturization and (2) the slowdown in the development speed of the data communication speed (Latency) between the CPU and the memory. Regarding the above problem (1), there is a call for replacing it with a low-power-consuming carrier, but the above problem (2) is also becoming prominent with the development of recent peripheral technologies.

[0003] For example, in a group of sensors (so-called artificial skin) that can detect sensations similar to those of humans, when access by conventional electronic devices is enabled, the number of transistors becomes enormous, the control unit becomes large, and at the same time, communication delay is caused. Also, regarding high-resolution three-dimensional displays in the medical and entertainment fields, although the viewing angle can be expanded (secured to about 45 degrees) so that multiple people can view simultaneously, when this is configured by electronic devices, the number of transistors also becomes enormous. Therefore, communication delay and heat generation in wiring cannot be ignored, and there are concerns about wiring burnout and unstable operation due to heat generation.

[0004] Thus, the number of scenarios where a large number of elements are essential has increased, and due to the rapid increase in integration density, the CMOS-based system has become a bottleneck for the entire application in terms of both speed and miniaturization.

[0005] Regarding the problems of such conventional CMOS-based systems, there is a technology that attempts to solve them using spin waves.

[0006] A spin wave is a phase wave created by magnetization (spin) within a magnetic material. It is also called a magnetostatic wave. Magnetic materials contain many spins, as shown in Figure 6. A wavefront is formed when the timing (phase) of these spins' rotations is aligned. When this wavefront propagates, information can be transmitted. This is a spin wave, and it allows information to be transmitted without the movement of electric charge. Spin waves are a phenomenon related only to the magnetism of a material and are not related to its electrical properties. That is, they propagate through magnetic materials, whether they are conductors or insulators. Therefore, it is possible to create wiring using insulators where electricity does not flow, but spin waves do. Furthermore, because spin waves are in the GHz (gigahertz) band, they are fast enough to be used for information processing.

[0007] Thus, spin waves are attracting attention as a potential next-generation ultra-low-power information processing device because they are an information transmission method that does not require charge transfer. Basic logic circuits such as XNOR circuits [see Non-Patent Document 1], AND circuits, and OR circuits [see Non-Patent Document 2] have already been demonstrated and are in the research stage. With the demonstration of basic elements, more complex and practical circuits and applications are being proposed, demonstrated, and patented. Recently, research has been disclosed that computationally demonstrated that compact address decoders can be fabricated using these spin waves (see Patent Document 1). In addition to the development of functionality, miniaturization of size is also progressing. It is expected that miniaturization will progress to the micrometer and nanoscale.

[0008] There are several methods for generating spin waves, but currently, the most common method involves using electric current to create them.

[0009] Patent Document 2 describes a coplanar web guide type (a single-layer type) spin wave excitation structure. This is a spin wave excitation structure (antenna) made of a single layer of copper wire for the signal level and copper wire for the ground level. A high-frequency electrical signal can be input using a structure like the one described in Patent Document 2. As mentioned above, this structure is called a coplanar web guide structure and is a widely known structure. It is widely used because the antenna part can be fabricated in a single layer and can be made as small as nanometer scale. However, there was a problem in that the frequency bandwidth of the spin waves (magnetostatic waves) that could be generated was narrow.

[0010] Patent Document 3 describes a microstrip line type spin wave excitation structure. A microstrip line is a structure in which a single copper wire carrying an electric current (signal level) is placed on a medium through which spin waves flow, and the ground level is provided below the medium through which spin waves flow (Patent Document 3 exemplified YIG (yttrium iron garnet)).

[0011] The microstrip line type structure disclosed in Patent Document 3 has the advantage of a wide bandwidth for the spin waves that can be generated. On the other hand, because it is a multi-stage structure in which the signal level and ground level cross the YIG, it is difficult to integrate.

[0012] As miniaturization and integration progress, and microstrip lines become thinner, the distance between the signal level and the ground level (= thickness of YIG) remains the same. As a result, it becomes difficult to create a high-frequency rotating magnetic field within a medium that allows spin waves to flow smoothly, and the spin wave intensity decreases. The closer the signal level and the more YIG there is between them, the stronger the spin wave intensity that can be excited becomes.

[0013] As the microstrip line is made thinner, one possible strategy to maintain spin wave intensity is to simultaneously thin the YIG (Yellow Isopropyl Alignment). However, when the thickness is less than 1 micrometer, the YIG cannot stand on its own (it will crack, for example). Therefore, YIG is generally handled on a substrate with a thickness of around 100 micrometers, and structural studies are conducted within that range.

[0014] Specifically, a conductive material called a microstrip line (often made of copper wire) is used, as shown in Figure 5(a). A copper film is deposited on the underside of the Teflon® substrate. The thickness of the copper film is approximately 10 μm. The copper wire on top of the Teflon® substrate is approximately 10 μm wide and 10 μm thick. When electricity is passed through this line, a rotating magnetic field is generated around the copper wire at a speed of approximately GHz. When a magnetic insulator (a material called YIG in Figure 5(a)) is placed in the area where this rotating magnetic field is generated, a spin wave is excited by the rotating magnetic field. As a result, the spin wave is transmitted from one microstrip line (input microstrip line) to the other microstrip line (output microstrip line). At the output microstrip line, conversely, the rotating magnetic field created by the spin wave generates an electric current within the microstrip line. That is, electricity is passed through to excite the spin wave, spin wave propagation occurs, calculations are performed during this propagation, the calculation results are propagated, the spin wave is converted back into an electric current, and detected as an electrical signal. In this way, a spin wave propagation spectrum like the one shown by the "magnetic field present" line in Figure 5(b) can be obtained. "Without YIG" in Figure 5(b) shows the spectrum when there is no YIG in the structure of Figure 5(a), and "Without magnetic field" in Figure 5(b) shows the spectrum when no DC magnetic field is applied in the structure of Figure 5(a). Referring to Figure 5(a), the input microstrip line is the spin wave excitation structure, and the output microstrip line is the spin wave detection structure. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 2017-162937 [Patent Document 2] Special Publication No. 2006-504345 [Patent Document 3] Japanese Patent Application Publication No. 1-91514 [Non-patent literature]

[0016] [Non-Patent Document 1] Taichi Goto, Takuya Yoshimoto, Bungo Iwamoto, Kei Shimada, Caroline A. Ross, Koji Sekiguchi, Alexander B. Granovsky, Yuichi Nakamura, Hironaga Uchida, and Mitsuteru Inoue, “Three port logic gate using forward volume spin wave interference in a thin yttrium iron garnet film”, Scientific Reports, 9, 16472 (2019 / 11 / 11). [Non-Patent Document 2] Naoki Kanazawa, Taichi Goto, Koji Sekiguchi, Alexander B. Granovsky, Caroline A. Ross, Hiroyuki Takagi, Yuichi Nakamura, Hironaga Uchida, and Mitsuteru Inoue, “The role of Snell's law for a magnonic majority gate”, Scientific Reports, 7, 7898 (2017 / 08 / 11). [Overview of the Initiative] [Problems that the invention aims to solve]

[0017] Spin wave devices, which are attracting attention as new information processing devices as described above, also have their challenges. One of these is the low intensity of the spin waves.

[0018] The currently used spin-wave excitation structure for electrical use (also known as a transducer or an antenna, which also serves as a spin-wave detection structure as described above) has a cross-sectional view as shown in FIG. 4. The conventional spin-wave excitation and detection structure 200 has a copper film 24 under a dielectric substrate 22, and a YIG film 26 is placed on a copper wire 28 together with a gadolinium gallium garnet substrate 25. This is not suitable for miniaturization and integration. This is because if it is miniaturized simply by scaling down, the excitation efficiency becomes extremely low and the bandwidth becomes extremely narrow.

[0019] The present invention has been made in view of the above problems, and an object thereof is to provide a spin-wave excitation and detection structure having high structural strength, high spin-wave intensity that can be excited, and a wide frequency bandwidth of spin waves that can be excited.

Means for Solving the Problems

[0020] In order to achieve the above object, the present invention provides a spin-wave excitation and detection structure for exciting and detecting spin waves, comprising a support substrate, a conductor film provided on the support substrate, an insulating magnetic film provided on the conductor film, and a conductor wire provided on the insulating magnetic film.

[0021] Such a spin-wave excitation and detection structure has high structural strength and high spin-wave intensity that can be excited. Also, the frequency bandwidth of spin waves that can be excited is wide.

[0022] Here, it is preferable that the insulating magnetic film is made of magnetic garnet. Further, it is preferable that the insulating magnetic film is made of yttrium iron garnet.

[0023] Since the insulating magnetic film is of such a type, good spin waves can be excited. Also, the detection of spin waves can be performed without problems.

[0024] Furthermore, the conductive film and conductive wire may comprise at least one of the following: copper, aluminum, gold, silver, platinum, iron, transparent conductor, superconductor, graphene, or conductive magnetic material.

[0025] In the spin wave excitation detection structure of the present invention, in addition to copper, the above-mentioned types of conductors can be used as a component of the conductor.

[0026] Furthermore, the support substrate can be at least one of the following: a silicon substrate, a dielectric substrate, a conductive substrate, an insulating substrate, a magnetic substrate, a non-magnetic substrate, a wood substrate, or a stone substrate.

[0027] In the spin wave excitation detection structure of the present invention, in addition to a silicon substrate, the above-mentioned types of substrates can be used as the support substrate.

[0028] Furthermore, it is preferable that the thickness of the insulating magnetic film is 10 μm or less.

[0029] Furthermore, it is preferable that the conductive wire has a thickness of 1 μm or less and a width of 5 μm or less.

[0030] Furthermore, it is preferable that the thickness of the conductive film is 1 μm or less.

[0031] Furthermore, it is preferable that the thickness of the support substrate is 100 μm or more and 500 μm or less.

[0032] The dimensions of the components of the spin wave excitation detection structure of the present invention are preferably as shown, allowing for miniaturization. [Effects of the Invention]

[0033] The spin wave excitation detection structure of the present invention has high structural strength and high excitable spin wave intensity. Furthermore, it has a wide frequency bandwidth for the excitable spin waves. More specifically, the spin wave excitation detection structure of the present invention has an insulating magnetic film and a support substrate connected by a conductive film. While possessing the wide excitation bandwidth characteristic of a microstrip line, the signal level and ground level are close together, and there is an insulating magnetic film between them, which is the region through which spin waves flow, resulting in high excitable spin wave intensity. Moreover, since the insulating magnetic film is bonded to the support substrate via a conductive film, the structure has high mechanical strength and is easy to handle. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic cross-sectional view showing an example of the spin wave excitation detection structure of the present invention. [Figure 2] This is a schematic cross-sectional view showing the spin wave excitation detection structure used in the example. [Figure 3] This graph shows the spin wave propagation spectra in the example and comparative example. [Figure 4] This is a schematic cross-sectional view showing the spin wave excitation detection structure used in the comparative example. [Figure 5] (a) is a perspective view showing a conventional microstrip-type spin wave excitation detection structure, and (b) is its spin wave propagation spectrum. [Figure 6] This is a schematic diagram to explain spin waves. [Modes for carrying out the invention]

[0035] The following describes embodiments of the present invention, but the present invention is not limited thereto.

[0036] As described above, the electrically powered spin wave excitation structure (also known as a transducer or antenna) currently in use, as shown in Figure 4, is not suitable for miniaturization and integration. This is because simply scaling down the structure results in extremely low excitation efficiency and an extremely narrow bandwidth. Specifically, if the upper copper wire 28 is made thinner and narrower to achieve miniaturization and integration, the spin wave intensity weakens. This is because the upper copper wire 28 and the lower copper film 24 are too far apart. Therefore, one might consider thinning the dielectric substrate 22, but this would prevent a rotating magnetic field from being generated in the upper YIG film 26. For this reason, the YIG film 26 needs to be located between the upper copper wire 28 and the lower copper film 24. Furthermore, if it is too thin, the sample will fall apart, so a substrate (dielectric substrate 22) is necessary.

[0037] Based on the problems with the conventional spin wave excitation detection structure 200 shown in Figure 4, the inventors devised the structure shown in Figure 1 as useful and confirmed its usefulness through calculations. Therefore, we propose the following structure of the present invention.

[0038] Figure 1 shows the spin wave excitation detection structure 100 of the present invention. The spin wave excitation detection structure 100 is capable of exciting spin waves. It is also capable of detecting spin waves. The spin wave excitation detection structure 100 comprises a support substrate 12, a conductive film 14 provided on the support substrate 12, an insulating magnetic film 16 provided on the conductive film 14, and a conductive wire 18 provided on the insulating magnetic film 16. That is, the support substrate 12, the conductive film 14, the insulating magnetic film 16, and the conductive wire 18 are stacked in this order.

[0039] The upper conductive wire 18 is set to the electrical signal level, and the lower conductive film 14 is set to the electrical ground level. By passing a gigahertz high-frequency signal between the two, a spin wave is excited in the insulating magnetic film 16.

[0040] The spin wave excitation detection structure 100 shown in Figure 1 can be fabricated by, for example, preparing an insulating magnetic film 16 on which conductive wires 18 have been deposited and a support substrate 12 on which a conductive film 14 has been deposited, and then bonding them together. Alternatively, it can be fabricated by preparing a YIG on which Cu wires have been deposited and a Si substrate on which a Cu film has been deposited, and then bonding them together. Furthermore, the insulating magnetic film 16 can be epitaxially grown on another growth substrate (not shown), and the growth substrate can be removed after bonding. For example, gadolinium gallium garnet Gd3Ga5O 12 Yttrium iron garnet (Y3Fe5O) is produced by liquid epitaxial growth on non-magnetic substrates such as (GGG). 12 A single crystal of (YIG) can be used as the insulating magnetic film 16, in which case the GGG substrate can be removed by grinding or the like.

[0041] In the spin wave excitation detection structure 100 shown in Figure 1, it is preferable that the insulating magnetic film 16 is made of magnetic garnet. In particular, it is preferable that the insulating magnetic film 16 is made of yttrium iron garnet (YIG). Note that yttrium iron garnet is Y3Fe5O 12 Based on this, the material can be modified by substituting the Y or Fe portion with other elements. The insulating magnetic film 16 being magnetic garnet, particularly yttrium iron garnet, allows for good excitation of spin waves. Furthermore, spin wave detection can be performed without problems. The thickness of the insulating magnetic film 16 is preferably 10 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less. Thus, in the spin wave excitation detection structure 100 of the present invention, the insulating magnetic film 16 can be made as thin as 10 μm or less.

[0042] Furthermore, in the spin wave excitation detection structure 100 shown in Figure 1, the conductive film 14 and conductive wire 18 may consist of at least one of the following: copper, aluminum, gold, silver, platinum, iron, transparent conductor, superconductor, graphene, or conductive magnetic material. Among these, copper is particularly preferred. Other conductors can also be used as the material for the conductive film 14 and conductive wire 18, such as carbon nanotubes or organic conductive materials. It is also preferable that the material for the conductive film 14 and conductive wire 18 has higher conductivity than the support substrate 12 or the insulating magnetic film 16. The components of the conductive film 14 and conductive wire 18 may be the same or different.

[0043] Of these, the conductive wire 18 preferably has a thickness of 1 μm or less and a width of 5 μm or less. A thickness of 0.5 μm or less is more preferable, and 0.1 μm or less is particularly preferable. A width of 2 μm or less is even more preferable, and 0.5 μm or less is particularly preferable. Furthermore, there is no particular lower limit to the thickness of the conductive wire 18, but if the thickness becomes too thin, the wire will separate completely and conductivity cannot be maintained, so a thickness of 0.01 μm or more is preferable. Also, one conductive wire 18 is sufficient for the upper part. However, there may be two or more.

[0044] Furthermore, it is preferable that the thickness of the conductive film 14 is 1 μm or less. This thickness is more preferably 0.5 μm or less, and particularly preferably 0.1 μm or less. There is no particular lower limit to the thickness of the conductive film 14, but if the thickness becomes too thin, the film will separate completely and conductivity cannot be maintained, so it is preferable that it be 0.01 μm or more.

[0045] Furthermore, in the spin wave excitation detection structure 100 shown in Figure 1, the support substrate 12 can be at least one of the following: a silicon substrate, a dielectric substrate, a conductive substrate, an insulating substrate, a magnetic substrate, a non-magnetic substrate, a wood substrate, or a stone substrate. Thus, a variety of support substrates can be used. Among these, silicon substrates are preferred as support substrates because they are inexpensive and of good quality. Examples of insulating substrates include glass, quartz, sapphire, aluminum nitride, and alumina. A paramagnetic garnet substrate can also be used as a non-magnetic substrate. The thickness of the support substrate 12 is preferably 100 μm or more and 500 μm or less. If the thickness of the support substrate 12 is 100 μm or more, the mechanical strength is high and it becomes easier to handle. Also, if the thickness of the support substrate 12 is 500 μm or less, sufficient mechanical strength can be ensured and is sufficient.

[0046] The dimensions of the components of the spin wave excitation detection structure 100 of the present invention are preferably as listed above, allowing for miniaturization.

[0047] As described above, the spin wave excitation detection structure of the present invention is expected to become an essential component in spin wave computers, which are said to be the next generation of CPUs, as a spin wave excitation structure (an element that converts electricity to spin waves).

[0048] Spin waves are phase waves that propagate with electrons fixed in place, and therefore, in principle, they have zero Joule heat loss, which would otherwise occur due to charge transfer. Moreover, YIG in particular is a magnetic oxide material, making it an insulator and eliminating the generation of eddy currents. Thus, spin waves, which have zero losses in principle due to both steady-state current and eddy currents, have the potential to replace all wiring, logic elements such as NAND and NOR gates, and other components realized in CMOS. In other words, it is expected that by combining them with nanotechnology, it will be possible to realize a cold computer that does not generate heat.

[0049] The following are some of the ripple effects of the spin wave excitation detection structure of the present invention on related fields.

[0050] (1) Computer This will have ripple effects across all fields that currently use computers, including devices that incorporate computing elements such as CPUs. In particular, it will be useful in situations where computers are needed at the millimeter and micrometer scales. Examples include sensors and microchips being incorporated into mobile devices, wearable devices, and home appliances.

[0051] (2) High frequency, wireless, and communications fields Spin waves, like microwaves, are waves that respond on the GHz order, but by converting them into waves that propagate through magnetic materials, their wavelength can be shortened by more than 100 times. In terms of device size, this means that the entire chip can be made 100 times smaller. Conventionally, miniaturization of analog high-frequency equipment has not progressed much, and they are far from being portable. Therefore, the realization of spin wave devices, including spin wave phase modulation elements, is expected to lead to the miniaturization of high-frequency equipment. [Examples]

[0052] The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0053] [Comparative Example] A conventional structure, as shown in Figure 4, was fabricated. The dielectric substrate 22 had a thickness of 500 μm, the copper film 24 had a thickness of 10 μm, the YIG film 26 had a thickness of 10 μm, and the copper wire 28 had a thickness of 10 μm and a width of 10 μm. The parameters of each material were as follows.

[0054] [Table 1]

[0055] The spin wave spectrum obtained using the spin wave excitation detection structure shown in Figure 4 was calculated. This is represented by the "Conventional Structure" in Figure 3.

[0056] From Figure 3, the spin wave intensity and spin wave bandwidth can be obtained, as follows. • Spin wave intensity: 1.17Oe (value of spin wave intensity at the operating frequency of 4.0GHz) • Spin wave bandwidth: 0.243 GHz (This represents the frequency range where the spin wave intensity at the operating frequency of 4.0 GHz is halved.) If we define the performance index as the product of these two values, it will be as follows: ·Performance index: 0.285GHz·Oe

[0057] [Examples] A spin wave excitation detection structure, as shown in Figure 2, which is the structure of the present invention, was fabricated. The structure in Figure 2 uses the predetermined materials for each component of the structure shown in Figure 1, and the dimensions are as shown in Figure 2. The parameters for each component are as follows.

[0058] [Table 2] The spin wave spectrum obtained from the structure shown in Figure 2 was calculated. This is represented by the "Inventive Structure" in Figure 3.

[0059] From Figure 3, the spin wave intensity and spin wave bandwidth can be obtained. These are as follows: • Spin wave intensity: 15.3Oe (value of spin wave intensity at the operating frequency of 4.0GHz) • Spin wave bandwidth: 1.62 GHz (This represents the frequency range where the spin wave intensity at the operating frequency of 4.0 GHz is halved.) If we define the performance index as the product of these two values, ·Performance index: 24.8GHz·Oe This is the result.

[0060] The spin wave intensity of Example 1 is 15 times greater, the bandwidth is 8 times greater, and the figure of merit is 6 times greater compared to the conventional structure of Comparative Example 1, demonstrating significant improvements and demonstrating its usefulness.

[0061] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0062] 12…Support substrate, 14... Conductive film, 16…Insulating magnetic film 18... Conductive wire, 100... Spin wave excitation detection structure, 22… Dielectric substrate, 24…Copper film, 25…Gadolinium gallium garnet substrate, 26…YIG film, 28...Copper wire, 200...Conventional spin wave excitation detection structure.

Claims

1. A spin wave excitation detection structure that excites and detects spin waves, Support substrate and A conductive film provided on the support substrate (except when the conductive film is a magnetic material), An insulating magnetic film provided on the conductive film, Conductive wires provided on the insulating magnetic film and A spin wave excitation detection structure comprising the following: capable of exciting the spin wave in the insulating magnetic film using the conductive wire as an electrical signal level and the conductive film as an electrical ground level, and capable of detecting the spin wave of the insulating magnetic film.

2. The spin wave excitation detection structure according to claim 1, characterized in that the insulating magnetic film is made of magnetic garnet.

3. The spin wave excitation detection structure according to claim 2, characterized in that the insulating magnetic film is made of yttrium iron garnet.

4. The conductive film comprises at least one of copper, aluminum, gold, silver, platinum, a transparent conductor, a superconductor, and graphene. The spin wave excitation detection structure according to any one of claims 1 to 3, characterized in that the conductive wire comprises at least one of copper, aluminum, gold, silver, platinum, iron, a transparent conductor, a superconductor, graphene, or a conductive magnetic material.

5. The spin wave excitation detection structure according to any one of claims 1 to 4, characterized in that the support substrate is at least one of a silicon substrate, a dielectric substrate, a conductive substrate, an insulating substrate, a magnetic substrate, a non-magnetic substrate, a wood substrate, or a stone substrate.

6. The spin wave excitation detection structure according to any one of claims 1 to 5, characterized in that the thickness of the insulating magnetic film is 10 μm or less.

7. The spin wave excitation detection structure according to any one of claims 1 to 6, characterized in that the conductive wire has a thickness of 1 μm or less and a width of 5 μm or less.

8. The spin wave excitation detection structure according to any one of claims 1 to 7, characterized in that the thickness of the conductive film is 1 μm or less.

9. The spin wave excitation detection structure according to any one of claims 1 to 8, characterized in that the thickness of the support substrate is 100 μm or more and 500 μm or less.

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