Switching element and planar antenna

Abstract

To provide a switching element capable of efficiently performing phase transition of a phase transition layer composed of a substance which performs metal-insulator phase transition.SOLUTION: The switching element includes a phase transition layer disposed on a signal line through which a signal to be transmitted and received propagates, the phase transition layer being made of a substance that undergoes a metal-insulator phase transition, a thermal conduction layer formed on a surface of the phase transition layer, the thermal conduction layer being an insulator having a higher thermal conductivity than the phase transition layer, and a heating element having a rectangular shape with a long side along a direction perpendicular to an extending direction of the signal line and a short side shorter than a side length of the phase transition layer, the heating element being thermally connected to the phase transition layer and the thermal conduction layer.SELECTED DRAWING: Figure 31

Description

[Technical Field]

[0001] The present disclosure relates to a switching element and a planar antenna. [Background technology]

[0002] A metal-insulator phase-change element (also called a phase-change element) contains a material that undergoes a metal-insulator phase transition near its phase-change temperature. For example, vanadium dioxide is a material that undergoes a metal-insulator phase transition at around 67 degrees Celsius. By using a heating element to control the temperature of the phase-change element, a switching element utilizing the metal-insulator phase transition can be realized. By arranging such switching elements in an array corresponding to a patch antenna, a phased array antenna can be constructed. For example, by using a thin-film transistor circuit (TFT circuit) including thin-film transistors (TFTs) as a driving circuit to individually control the temperature of multiple phase-change elements, a phased array antenna that can transmit radio waves in a desired direction can be realized.

[0003] Patent Document 1 discloses a switching element including a vanadium dioxide thin film. The switching element of Patent Document 1 includes a substrate on which a vanadium dioxide thin film is formed, and a pair of electrodes, namely, gate electrodes, spaced apart from each other and provided on the vanadium dioxide thin film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-224390 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses an example in which a vanadium dioxide thin film is formed on an α-alumina substrate. The α-alumina substrate is a substrate suitable for the crystallization of vanadium dioxide. The α-alumina substrate has a higher thermal conductivity than vanadium dioxide. Therefore, if the size of the heating element is too small relative to the vanadium dioxide layer, heat applied to the vanadium dioxide layer tends to escape to the α-alumina substrate, making it difficult to efficiently heat the vanadium dioxide layer. Increasing the size of the heating element allows for efficient heating of the vanadium dioxide layer, thereby efficiently transitioning the vanadium dioxide layer to a metallic phase. However, if the size of the heating element is too large, the proximity of the heating element to the signal line increases the likelihood of high-frequency coupling. Therefore, it is necessary to efficiently transition the vanadium dioxide thin film (phase transition layer) to a metallic phase without increasing the size of the heating element too much.

[0006] An object of the present disclosure is to provide a switching element and a planar antenna that can efficiently transition a phase transition layer made of a material that undergoes a metal-insulator phase transition. [Means for solving the problem]

[0007] A switching element according to one embodiment of the present disclosure includes: a phase transition layer made of a material that undergoes a metal-insulator phase transition and disposed on a signal line along which a signal to be transmitted or received propagates; a thermally conductive layer that is an insulator having a higher thermal conductivity than the phase transition layer and is formed on the surface of the phase transition layer; and a heating element that is rectangular in shape with long sides perpendicular to the extension direction of the signal line and short sides shorter than the side lengths of the phase transition layer, and is thermally connected to the phase transition layer and the thermally conductive layer.

[0008] A planar antenna according to one embodiment of the present disclosure includes: an antenna substrate on which an antenna array composed of a plurality of patch antennas arranged in an array and switching elements corresponding to each of the plurality of patch antennas are disposed; and a temperature control substrate on which a thin-film transistor circuit is disposed for controlling the temperature of the switching elements corresponding to each of the plurality of patch antennas, wherein the switching elements are made of a material that undergoes a metal-insulator phase transition, and the planar antenna includes a phase transition layer disposed on a signal line along which a signal to be transmitted or received propagates; a thermally conductive layer formed on the surface of the phase transition layer and made of an insulator with a higher thermal conductivity than the phase transition layer; and a heating element thermally connected to the phase transition layer and the thermally conductive layer, the heating element being rectangular in shape with long sides perpendicular to the extension direction of the signal line and short sides shorter than the side length of the phase transition layer. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a switching element and a planar antenna that can efficiently transition a phase transition layer made of a material that undergoes a metal-insulator phase transition. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 2] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 3] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 4] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 5] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 6] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 7] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 8]FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 9] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 10] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 11] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 12] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 13] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 14] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 15] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 16] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 17] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 18] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 19] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 20] FIG. 1 is a conceptual diagram illustrating an example of an extension structure of a phase shifter according to the present disclosure. [Figure 21] FIG. 1 is a conceptual diagram illustrating an example of an extension structure of a phase shifter according to the present disclosure. [Figure 22] FIG. 1 is a conceptual diagram illustrating an example of an extension structure of a phase shifter according to the present disclosure. [Figure 23] FIG. 10 is a conceptual diagram illustrating an example of heat conduction in an extended structure of a phase shifter according to the present disclosure. [Figure 24] FIG. 1 is a conceptual diagram illustrating an example of an extension structure of a phase shifter according to the present disclosure. [Figure 25] FIG. 1 is a conceptual diagram illustrating an example of an extension structure of a phase shifter according to the present disclosure. [Figure 26] FIG. 1 is a conceptual diagram illustrating an example of an extension structure of a phase shifter according to the present disclosure. [Figure 27] FIG. 10 is a conceptual diagram illustrating an example of heat conduction in an extended structure of a phase shifter according to the present disclosure. [Figure 28] 1 is a conceptual diagram illustrating an example of the configuration of an antenna device according to the present disclosure. [Figure 29] 1 is a conceptual diagram showing a cross section of a portion of a planar antenna included in an antenna device according to the present disclosure. [Figure 30] 1 is a block diagram illustrating an example of a configuration of an antenna device according to the present disclosure. [Figure 31] FIG. 2 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. [Figure 32] FIG. 2 is a block diagram illustrating an example of a hardware configuration for executing control in the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In this disclosure, the drawings used in describing each embodiment relate to one or more embodiments. Furthermore, elements included in each drawing may apply to one or more embodiments. The embodiments described below are limited to technically preferable aspects for carrying out the present disclosure, but do not limit the scope of the disclosure to the following. In all drawings used in describing the following embodiments, similar parts are designated by the same reference numerals unless otherwise specified. In the following embodiments, repeated explanations of similar configurations and operations may be omitted.

[0012] (First embodiment) First, a switching element according to a first embodiment will be described with reference to the drawings. The switching element according to the present disclosure is one of metal-insulator phase transition elements (also referred to as phase transition elements) that contain a material that undergoes a metal-insulator phase transition. For example, the switching element according to the present disclosure may also be referred to as a phase transition switching element, a switching element, or a phase transition switch. In the following, an example will be given in which vanadium dioxide is used as the material that undergoes a metal-insulator phase transition. Vanadium dioxide undergoes a metal-insulator phase transition at around 67 degrees Celsius. A material that undergoes a metal-insulator phase transition other than vanadium dioxide may also be used in the switching element according to the present disclosure.

[0013] For example, the switching element of this embodiment is mounted on a planar antenna including multiple patch antennas. By mounting the switching element of this embodiment on each of the multiple patch antennas, a phased array antenna that transmits directional radio waves can be configured. Such a planar antenna is used to transmit and receive electromagnetic waves in the high-frequency band that is expected to be applied to B5G (Beyond 5th Generation) mobile communications, which follows 5G (5th Generation). Note that the switching element of this embodiment can be mounted on any device, not just a planar antenna.

[0014] (composition) FIG. 1 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. FIG. 1 is a plan view of the switching element viewed from above. The switching element 10 includes a phase change layer V and a heating element H. When viewed from above, the phase change layer V and the heating element H are disposed below an insulating layer 16. The formation area of ​​the phase change layer V is indicated by a dashed line. The formation area of ​​the heating element H is indicated by a dot-dash line. The heating element H is disposed on the upper surface of the phase change layer V. A thermally conductive layer (described below) is disposed on the lower surface of the phase change layer V. The phase change layer V is electrically connected to a first signal line S1 and a second signal line S2 via a connection terminal C. The first signal line S1 and the second signal line S2 are collectively referred to as signal lines.

[0015] The phase transition layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase transition layer V is a phase transition switching element that utilizes the phase transition between the insulating phase and the metallic phase of vanadium dioxide. In other words, the switching element 10 is an example of a phase transition element that utilizes a metal-insulator phase transition. The phase transition layer V may be made of a material other than vanadium dioxide. For example, the phase transition layer V may be made of a material such as a composite oxide containing vanadium dioxide or an oxide containing a 3d transition metal. The phase transition layer V may be made of a material with a transition temperature that corresponds to the environmental temperature. For example, the phase transition layer V may be made of a material that undergoes a phase transition at a temperature that can be used in the usage environment of the planar antenna.

[0016] For example, the phase transition layer V may contain vanadium dioxide without any additive element. In this case, the ratio of oxygen to vanadium contained in the vanadium dioxide is adjusted to a ratio at which a phase transition between an insulating phase and a metallic phase occurs. For example, the vanadium dioxide contained in the phase transition layer V may contain an additive element. For example, when an additive element such as tungsten, magnesium, tantalum, iron, molybdenum, fluorine, or niobium is added to vanadium dioxide, the phase transition temperature decreases. For example, when chromium, aluminum, or germanium is added to vanadium dioxide, the phase transition temperature increases.

[0017] At temperatures lower than the phase transition temperature, vanadium dioxide is in an insulating phase. Therefore, at temperatures lower than the phase transition temperature, the phase transition layer V is an insulator, and the switching element 10 is in an OFF state. At temperatures higher than the phase transition temperature, vanadium dioxide is in a metallic phase. Therefore, at temperatures higher than the phase transition temperature, the phase transition layer V is in a metallic phase, and the switching element 10 is in an ON state. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0018] For example, the phase transition layer V may be formed by a sputtering method or a pulse laser method using a target of metal vanadium or vanadium dioxide. Alternatively, the phase transition layer V may be formed by a sol-gel method, an inkjet method, or screen printing.

[0019] In this embodiment, three configuration examples are given for the switching element 10. In the following, the configuration examples of the switching element 10 are distinguished by adding a hyphen (-) and a number after the reference symbol (10).

[0020] [Configuration Example 1-1] 2 is a conceptual diagram showing an example of the configuration (configuration example 1-1) of a switching element according to the present disclosure, and is a cross-sectional view of the switching element taken along the line AA in FIG.

[0021] The switching element 10-1 includes a substrate 11, a thermally conductive layer 12, a phase change layer V, a heating element H, and an insulating layer 16. The substrate 11, the thermally conductive layer 12, the phase change layer V, and the heating element H are covered with the insulating layer 16. The phase change layer V is electrically connected to a first signal line S1 and a second signal line S2 through openings formed in the insulating layer 16. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0022] The substrate 11 is an insulator (dielectric). The substrate 11 has a lower thermal conductivity than the phase transition layer V. The substrate 11 is made of a material with low dielectric loss. The substrate 11 is preferably made of a material with high insulation and low dielectric loss, such as a ceramic material or glass. The substrate 11 may be made of a polymer or synthetic material. The lower the dielectric loss of the substrate 11, the more effectively it can control electromagnetic waves such as high frequency waves and microwaves.

[0023] The thermally conductive layer 12 is disposed on the upper surface of the substrate 11. A phase transition layer V is disposed on the upper surface of the thermally conductive layer 12. The thermally conductive layer 12 is made of a material with a higher thermal conductivity than the substrate 11 and the phase transition layer V. There are no limitations on the material of the thermally conductive layer 12, as long as it is made of a material with a higher thermal conductivity than the substrate 11. For example, the thermally conductive layer 12 may be made of alpha alumina. Alpha alumina has a high lattice match with vanadium dioxide, making it easy to crystallize vanadium dioxide. Therefore, an alpha alumina substrate is a suitable substrate for crystallizing vanadium dioxide. For example, the thermally conductive layer 12 may be made of silicon carbide. Silicon carbide has a crystal system with thermal conductivity comparable to that of metals.

[0024] The phase change layer V is disposed on the upper surface of the thermally conductive layer 12. The heating element H is disposed on the upper surface of the phase change layer V. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when heated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection terminal C. The phase change layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch.

[0025] When the switching element 10-1 is mounted on a planar antenna, the first signal line S1 is connected to a signal source (not shown) via a phase-shift wiring (not shown). For example, the first signal line S1 is configured as a line through which a signal phase-shifted by the phase-shift wiring propagates. For example, the second signal line S2 is configured as a line through which the phase-shifted signal propagates to a patch antenna and extends below the patch antenna. The layer on which the phase transition layer V, the first signal line S1, and the second signal line S2 are arranged forms a phase-shift layer. For example, the signal that reaches the second signal line S2 propagates to the patch antenna by electromagnetic coupling. For example, the signal that reaches the second signal line S2 may be configured to propagate to the patch antenna via a conductor such as a via.

[0026] The heating element H is disposed on the upper surface of the phase transition layer V. The heating element H has an elongated rectangular shape extending perpendicular to the direction in which the first signal line S1 and the second signal line S2 extend. That is, the heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the phase transition layer V disposed on the lower surface of the heating element H. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0027] The heating element H is made of a material with high electrical resistance that easily generates heat when current is applied. For example, the heating element H is made of a material containing a nickel-chromium alloy or a chromium-iron-aluminum alloy. The selected heating element H is configured to generate heat up to a temperature at which the vanadium dioxide contained in the phase transition layer V undergoes a phase transition to a metallic phase. When the heating element H is not generating heat, the vanadium dioxide contained in the phase transition layer V is in an insulating phase. When the vanadium dioxide contained in the phase transition layer V is in an insulating phase, the switching element 10-1 is in an off state.

[0028] The insulating layer 16 covers the substrate 11, the thermally conductive layer 12, the phase change layer V, and the heating element H. The insulating layer 16 has openings above two opposing ends of the phase change layer V. The connection ends C of the first signal line S1 and the second signal line S2 are electrically connected to the phase change layer V through the openings formed in the insulating layer 16. For example, the insulating layer 16 is made of an insulating material such as silicon dioxide. The thermal conductivity of the insulating layer 16 is similar to that of the substrate 11. That is, the thermal conductivity of the insulating layer 16 is lower than that of the phase change layer V.

[0029] When the heating element H generates heat in response to a selection made via the TFT circuit, the heat from the heating element H is conducted to the phase transition layer V. The heat conducted to the phase transition layer V is then conducted to the thermally conductive layer 12 disposed below the phase transition layer V. The thermally conductive layer 12 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted in the thermally conductive layer 12 is then conducted to the phase transition layer V disposed above it. As a result, the phase transition layer V is uniformly heated via the thermally conductive layer 12 disposed below it. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the connection terminal C. When the temperature exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 10-1 transitions to the on state. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase, which causes the switching element 10-1 to transition to the off state.

[0030] To efficiently heat the phase change layer V, it is preferable to increase the contact area between the phase change layer V and the heating element. However, if the heating element is too close to the first signal line S1 and the second signal line S2, high-frequency coupling is likely to occur. If the thermal conductivity of the substrate 11 is higher than that of the phase change layer V, the phase change layer V can be heated uniformly from below. However, if the thermal conductivity of the substrate 11 is higher than that of the phase change layer V, the heat to be conducted to the phase change layer V is more likely to be dissipated through the substrate 11.

[0031] In this configuration example, heat is conducted to the phase transition layer V via the thermally conductive layer 12, which has a higher thermal conductivity than the phase transition layer V. In this configuration example, the thermally conductive layer 12 is disposed between the phase transition layer V and the substrate 11, which has a lower thermal conductivity than the phase transition layer V. This makes it difficult for heat to escape to the substrate 11. Therefore, this configuration example allows the phase transition layer V to be heated more efficiently than when the thermally conductive layer 12 is not present. Furthermore, in this configuration example, because heat is difficult to escape to the substrate 11, the size of the heating element H can be reduced. Therefore, in this configuration example, by forming the heating element H into an elongated rectangular shape, high-frequency coupling between the first signal line S1 and the second signal line S2 and the heating element H is unlikely to occur.

[0032] [Configuration Example 1-2] 3 is a conceptual diagram showing an example of the configuration of a switching element (Configuration Example 1-2) according to the present disclosure. FIG. 3 is a cross-sectional view of the switching element taken along the AA cutting line in FIG. 1. This configuration example differs from Configuration Example 1-1 in that it includes a heat conduction promotion layer. In the following, a description of the same configuration as Configuration Example 1-1 will be omitted.

[0033] The switching element 10-2 includes a substrate 11, a thermally conductive layer 12, a thermal conduction promotion layer 13, a phase change layer V, a heat-generating element H, and an insulating layer 16. The substrate 11, the thermally conductive layer 12, the thermal conduction promotion layer 13, the phase change layer V, and the heat-generating element H are covered with the insulating layer 16. The phase change layer V is electrically connected to a first signal line S1 and a second signal line S2. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0034] The thermal conduction promotion layer 13 is disposed on the upper surface of the substrate 11. The thermal conduction layer 12 is disposed on the upper surface of the thermal conduction promotion layer 13. The thermal conduction promotion layer 13 is made of a material having a higher thermal conductivity than the substrate 11 and the thermal conduction layer 12. In other words, the thermal conduction promotion layer 13 has a higher thermal conductivity than the substrate 11 and the thermal conduction layer 12. There are no limitations on the material of the thermal conduction promotion layer 13 as long as it is made of a material having a higher thermal conductivity than the substrate 11 and the thermal conduction layer 12. For example, the thermal conduction promotion layer 13 is made of silicon carbide. Silicon carbide has a crystal system whose thermal conductivity is comparable to that of metals.

[0035] The thermal conduction layer 12 is disposed on the upper surface of the thermal conduction promotion layer 13. A phase transition layer V is disposed on the upper surface of the thermal conduction layer 12. The thermal conduction layer 12 is made of a material with a higher thermal conductivity than the substrate 11 and the phase transition layer V. The thermal conduction layer 12 is made of a material with a lower thermal conductivity than the thermal conduction promotion layer 13. There are no limitations on the material of the thermal conduction layer 12, as long as it is made of a material with a higher thermal conductivity than the substrate 11 and a lower thermal conductivity than the thermal conduction promotion layer 13. For example, the thermal conduction layer 12 includes sapphire (alumina). Sapphire is a suitable material for the thermal conduction layer 12 because the crystallinity of vanadium dioxide is improved when used as a base. In this way, when sapphire is used for the thermal conduction layer 12, the thermal conduction layer 12 functions as a layer for improving the crystallinity of vanadium dioxide. Compared to silicon carbide, sapphire is advantageous for the crystal growth of vanadium dioxide. Therefore, if sapphire is configured to function as a crystallinity improving layer and silicon carbide is configured to function as a heat conduction promoting layer (heat conduction layer), the phase transition layer V can be heated efficiently.

[0036] The phase change layer V is disposed on the upper surface of the thermally conductive layer 12. The heating element H is disposed on the upper surface of the phase change layer V. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when heated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection terminal C. The phase change layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch.

[0037] When the heating element H generates heat in response to a selection made via the TFT circuit, the heat from the heating element H is conducted to the vanadium dioxide contained in the phase transition layer V. The heat conducted to the phase transition layer V is then conducted to the thermally conductive layer 12 disposed on the lower surface of the phase transition layer V. The thermally conductive layer 12 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted to the thermally conductive layer 12 is then conducted to the thermal conduction promotion layer 13 disposed on the lower surface of the thermally conductive layer 12. The thermal conduction promotion layer 13 has a higher thermal conductivity than the thermally conductive layer 12, and therefore conducts heat more efficiently than the thermally conductive layer 12. The heat conducted in the thermal conduction promotion layer 13 is then conducted to the thermally conductive layer 12 disposed on the upper surface. The heat conducted in the thermally conductive layer 12 and the heat conducted from the thermal conduction promotion layer 13 to the thermally conductive layer 12 are conducted to the phase transition layer V disposed on the upper surface. As a result, the phase transition layer V is uniformly heated via the thermal conduction layer 12 and the thermal conduction promotion layer 13 disposed on its underside. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the connection terminal C. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 10-2 transitions to the ON state. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase. When the vanadium dioxide undergoes a phase transition to the insulating phase, the switching element 10-2 transitions to the OFF state.

[0038] In this configuration example, heat is conducted to the phase transition layer V via the thermal conduction layer 12 and the thermal conduction promotion layer 13, which have higher thermal conductivity than the phase transition layer V. In this configuration example, the thermal conduction layer 12 and the thermal conduction promotion layer 13 are disposed between the phase transition layer V and the substrate 11, which has lower thermal conductivity than the phase transition layer V. This makes it difficult for heat to escape to the substrate 11. In this configuration example, the inclusion of the thermal conduction promotion layer 13 allows the phase transition layer V to be heated more efficiently than in configuration example 1-1. Furthermore, in this configuration example, because heat is less likely to escape to the substrate 11, the size of the heating element H can be made smaller than in configuration example 1-1. Therefore, in this configuration example, high-frequency coupling between the first signal line S1 and the second signal line S2 and the heating element H is less likely to occur than in configuration example 1-1.

[0039] In this configuration example, the thermally conductive layer 12 is disposed on the lower surface of the phase change layer V, and the thermal conduction promotion layer 13 is disposed on the lower surface of the thermally conductive layer 12. For example, the thermal conduction promotion layer 13 may be disposed on the lower surface of the phase change layer V, and the thermal conduction promotion layer 12 may be disposed on the lower surface of the thermal conduction promotion layer 13. For example, a thermally conductive layer other than the thermally conductive layer 12 and the thermal conduction promotion layer 13 may be disposed on the lower surface of the phase change layer V. For example, a thermally conductive structure including the thermally conductive layer 12 and the thermal conduction promotion layer 13 may be disposed on the upper surface of the phase change layer V.

[0040] [Configuration Example 1-3] 4 is a conceptual diagram showing an example of the configuration of a switching element (Configuration Example 1-3) according to the present disclosure. FIG. 4 is a cross-sectional view of the switching element taken along the AA cutting line in FIG. 1. In this configuration example, the heat conduction promotion layer is disposed at a position different from that in Configuration Example 1-2. In the following, descriptions of the same configurations as in Configuration Examples 1-1 and 1-2 will be omitted.

[0041] The switching element 10-3 includes a substrate 11, a thermally conductive layer 12, a thermal conduction promotion layer 13, a phase change layer V, a heat-generating element H, and an insulating layer 16. The substrate 11, the thermally conductive layer 12, the thermal conduction promotion layer 13, the phase change layer V, and the heat-generating element H are covered with the insulating layer 16. The phase change layer V is electrically connected to a first signal line S1 and a second signal line S2. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0042] The thermally conductive layer 12 is disposed on the upper surface of the substrate 11. The phase transition layer V is disposed on the upper surface of the thermally conductive layer 12. The thermally conductive layer 12 is made of a material having a higher thermal conductivity than the substrate 11 and the phase transition layer V. In other words, the thermally conductive layer 12 has a higher thermal conductivity than the substrate 11 and the phase transition layer V.

[0043] The phase change layer V is disposed on the upper surface of the thermal conduction layer 12. A thermal conduction promotion layer 13 is disposed on the upper surface of the phase change layer V. A heating element H is disposed above the phase change layer V, with the thermal conduction promotion layer 13 interposed therebetween. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when heated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection terminal C. The phase change layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch.

[0044] The thermal conduction promotion layer 13 is disposed on the upper surface of the phase transition layer V. The upper surface of the thermal conduction promotion layer 13 is covered with an insulating layer 16. A through hole reaching the phase transition layer V is formed in a part of the thermal conduction promotion layer 13. The connection ends C of the first signal line S1 and the second signal line S2 are disposed in the through hole formed in the thermal conduction promotion layer 13. The thermal conduction promotion layer 13 is made of a material having a higher thermal conductivity than the phase transition layer V and the thermal conduction layer 12. That is, the thermal conduction promotion layer 13 has a higher thermal conductivity than the phase transition layer V and the thermal conduction layer 12.

[0045] When the heating element H generates heat in response to selection via the TFT circuit, the heat is conducted to the thermal conduction promotion layer 13 disposed on the upper surface of the phase transition layer V. The heat conducted to the thermal conduction promotion layer 13 is conducted inside the thermal conduction promotion layer 13 and conducted to the phase transition layer V at the lower surface of the thermal conduction promotion layer 13. The thermal conduction promotion layer 13 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. Heat is conducted to the vanadium dioxide contained in the phase transition layer V via the thermal conduction promotion layer 13. The heat conducted to the phase transition layer V is also conducted to the thermal conductive layer 12 disposed on the lower surface of the phase transition layer V. The thermal conductive layer 12 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted in the thermal conductive layer 12 is conducted to the phase transition layer V disposed on the upper surface. As a result, the phase transition layer V is uniformly heated via the thermal conduction promotion layer 13 disposed on the upper surface and the thermal conductive layer 12 disposed on the lower surface. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the connection terminal C. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 10-3 transitions to the ON state. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase. When the vanadium dioxide undergoes a phase transition to the insulating phase, the switching element 10-3 transitions to the OFF state.

[0046] In this configuration example, the phase transition layer V is sandwiched between the thermal conduction layer 12 and the thermal conduction promotion layer 13. In this configuration example, heat is conducted to the phase transition layer V via the thermal conduction layer 12 and the thermal conduction promotion layer 13, which have higher thermal conductivity than the phase transition layer V. In this configuration example, the phase transition layer V is sandwiched between the thermal conduction layer 12 and the thermal conduction promotion layer 13, which have higher thermal conductivity than the phase transition layer V. This makes it difficult for heat to escape to the substrate 11, and the phase transition layer V can be heated more efficiently than in configuration examples 1-1 to 1-2. Furthermore, in this configuration example, because heat is difficult to escape to the substrate 11, the size of the heating element H can be made smaller than in configuration examples 1-1 to 1-2. Therefore, in this configuration example, high-frequency coupling between the first signal line S1 and the second signal line S2 and the heating element H is less likely to occur than in configuration examples 1-1 to 1-2.

[0047] In this configuration example, the thermal conduction promotion layer 13 is disposed on the upper surface of the phase change layer V, and the thermal conduction layer 12 is disposed on the lower surface of the phase change layer V. For example, the thermal conduction layer 12 may be disposed on the upper surface of the phase change layer V, and the thermal conduction promotion layer 13 may be disposed on the lower surface of the phase change layer V. For example, the thermal conduction layers 12 may be disposed on both surfaces of the phase change layer V. For example, the thermal conduction promotion layers 13 may be disposed on both surfaces of the phase change layer V. For example, the thermal conduction layer 12 and the thermal conduction promotion layer 13 may be disposed on the upper surface of the heat-generating element H.

[0048] As described above, the switching element of this embodiment includes a substrate, a phase change layer, a thermally conductive layer, and a heating element. The substrate is an insulator with lower thermal conductivity than the phase change layer and the thermally conductive layer. The phase change layer is made of a material that undergoes a metal-insulator phase transition. For example, the phase change layer contains vanadium dioxide as a material that undergoes a metal-insulator phase transition. The phase change layer is disposed on a signal line through which a signal to be transmitted or received propagates. The thermally conductive layer is an insulator with higher thermal conductivity than the phase change layer. The thermally conductive layer is formed between the substrate and the phase change layer. The heating element is rectangular, with long sides perpendicular to the extension direction of the signal line and short sides shorter than the sides of the phase change layer. The heating element is thermally connected to the phase change layer and the thermally conductive layer. The heating element is disposed above the phase change layer.

[0049] The switching element of this embodiment includes a phase transition layer made of a material that undergoes a metal-insulator phase transition. A thermally conductive layer having a higher thermal conductivity than the phase transition layer is formed on the surface of the phase transition layer. The phase transition layer and the thermally conductive layer are thermally connected to a heating element. When the heating element generates heat, the phase transition layer is uniformly heated via the thermally conductive layer formed on the surface. Therefore, according to the configuration of this embodiment, even if the size of the heating element is reduced, the phase transition layer made of a material that undergoes a metal-insulator phase transition can be efficiently phase-transitioned. Furthermore, according to the configuration of this embodiment, by forming the heating element into an elongated rectangular shape, high-frequency coupling between the signal line and the heating element is less likely to occur.

[0050] In one aspect of this embodiment, the phase change layer is disposed between the heating element and the thermally conductive layer. In this aspect, heat conducted to the thermally conductive layer through the phase change layer is conducted in the thermally conductive layer faster than in the phase change layer. Because the heat conducted in the thermally conductive layer returns to the phase change layer, the phase change layer is easily heated uniformly. Therefore, this embodiment allows the phase change of the phase change layer to occur efficiently.

[0051] The switching element of one aspect of this embodiment includes a thermal conduction facilitating layer. The thermal conduction facilitating layer is an insulator with a higher thermal conductivity than the thermal conduction layer and is thermally connected to the phase change layer. For example, the thermal conduction facilitating layer is disposed between the substrate and the thermal conduction layer. For example, the thermal conduction facilitating layer is disposed between the phase change element and the heat generating element. According to this aspect, the thermal conduction facilitating layer, which has a higher thermal conductivity than the thermal conduction layer, allows the phase change of the phase change layer to occur more efficiently.

[0052] (Second embodiment) Next, a switching element according to a second embodiment will be described with reference to the drawings. The switching element according to this embodiment differs from the switching element according to the first embodiment in the positional relationship between the phase transition layer and the heating element. In the following, the description of the same configuration as the first embodiment will be simplified or omitted.

[0053] (composition) FIG. 5 is a conceptual diagram illustrating an example of the configuration of a switching element according to the present disclosure. FIG. 5 is a plan view of the switching element viewed from above. The switching element 20 includes a phase change layer V and a heating element H. When viewed from above, the phase change layer V and the heating element H are disposed below the insulating layer 26. The formation area of ​​the phase change layer V is indicated by a dashed line. The formation area of ​​the heating element H is indicated by a dot-dash line. The heating element H is disposed below the phase change layer V. A thermally conductive layer (described below) is disposed on the underside of the phase change layer V. The heating element H is disposed below the phase change layer V via the thermally conductive layer. The phase change layer V is electrically connected to a first signal line S1 and a second signal line S2 via a connection terminal C.

[0054] The phase transition layer V has the same configuration as the phase transition layer V in the first embodiment. The phase transition layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. Vanadium dioxide is in the insulating phase at temperatures lower than the phase transition temperature. Therefore, the switching element 20 is in the off state at temperatures lower than the phase transition temperature. Vanadium dioxide is in the metallic phase at temperatures higher than the phase transition temperature. Therefore, the switching element 20 is in the on state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0055] In this embodiment, two configuration examples are given for the switching element 20. In the following, the configuration examples of the switching element 20 are distinguished by adding a hyphen (-) and a number after the reference symbol (20).

[0056] [Configuration Example 2-1] 6 is a conceptual diagram showing an example of the configuration of a switching element (configuration example 2-1) according to the present disclosure, and is a cross-sectional view of the switching element taken along line BB in FIG.

[0057] The switching element 20-1 includes a substrate 21, a thermally conductive layer 22, a phase change layer V, a heating element H, an insulating layer 26, and an insulating layer 27. The insulating layer 27 is formed on the upper surface of the substrate 21. A through hole is formed in the insulating layer 27. The heating element H is embedded in the through hole of the insulating layer 27. The thermally conductive layer 22 and the phase change layer V are disposed above the insulating layer 27 and the heating element H. The thermally conductive layer 22 and the phase change layer V are covered by the insulating layer 26. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 through the through hole formed in the insulating layer 26. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0058] The substrate 21 has the same configuration as the substrate 11 of the first embodiment. The substrate 21 is an insulator (dielectric). The substrate 21 has a lower thermal conductivity than the phase transition layer V.

[0059] The thermally conductive layer 22 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 22 is disposed on the upper surface of the insulating layer 27 in which the heat generating elements H are embedded. A phase transition layer V is disposed on the upper surface of the thermally conductive layer 22. The thermally conductive layer 22 is made of a material having a higher thermal conductivity than the substrate 21, the insulating layer 27, and the phase transition layer V.

[0060] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V is disposed on the upper surface of the thermally conductive layer 22. Heat generated by the heating element H is conducted to the phase change layer V via the thermally conductive layer 22. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase in response to heat generated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection terminal C. The phase change layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch.

[0061] The heating element H has the same configuration as in the first embodiment. The heating element H is disposed on the lower surface of the thermally conductive layer 22. The heating element H has an elongated rectangular shape extending perpendicular to the direction in which the first signal line S1 and the second signal line S2 extend. The heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted via the thermally conductive layer 22 to the phase transition layer V disposed above the heating element H. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0062] The insulating layer 26 has a configuration similar to that of the insulating layer 16 of the first embodiment. The insulating layer 26 covers the thermally conductive layer 22 and the phase change layer V. The insulating layer 26 has openings above two opposing ends of the phase change layer V. The connection ends C of the first signal line S1 and the second signal line S2 are electrically connected to the phase change layer V through the openings formed in the insulating layer 26. The thermal conductivity of the insulating layer 26 is similar to that of the substrate 21. That is, the thermal conductivity of the insulating layer 26 is lower than that of the phase change layer V.

[0063] The insulating layer 27 is formed on the upper surface of the substrate 21. Through holes are formed in the insulating layer 27 for arranging the heating elements H. The heating elements H are embedded in the through holes of the insulating layer 27. For example, the insulating layer 27 is made of an insulating material such as silicon dioxide. If the surface of the phase transition layer V formed on the insulating layer 27 is uneven, these unevenness may become singular points and cause signal reflection. For this reason, the upper surface of the insulating layer 27 is planarized. For example, the upper surface of the insulating layer 27 is planarized using a technique such as chemical mechanical polishing (CMP). The thermal conductivity of the insulating layer 27 is similar to that of the substrate 21 and the insulating layer 26. That is, the thermal conductivity of the insulating layer 27 is lower than that of the phase transition layer V.

[0064] When the heating element H generates heat in response to selection via the TFT circuit, the heat is conducted to the thermally conductive layer 22 disposed on the upper surface of the heating element H. The heat conducted to the thermally conductive layer 22 is then conducted to the phase transition layer V disposed on the upper surface. The thermally conductive layer 22 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. As a result, the phase transition layer V is uniformly heated via the thermally conductive layer 22 disposed on the lower surface. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the connection terminal C. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 20-1 transitions to the on state. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase. When the vanadium dioxide undergoes a phase transition to the insulating phase, the switching element 20-1 transitions to the OFF state.

[0065] In this configuration example, heat is conducted to the phase transition layer V via the thermally conductive layer 22, which has a higher thermal conductivity than the phase transition layer V. In this configuration example, the heating element H is in direct contact with the thermally conductive layer 22, so that heat from the heating element H is easily conducted to the thermally conductive layer 22 and is less likely to escape to the substrate 21. Therefore, this configuration example can heat the phase transition layer V more efficiently than the first embodiment. Furthermore, in this configuration example, the first signal line S1 and the second signal line S2 can be disposed farther away from the heating element H. Therefore, in this configuration example, high-frequency coupling between the first signal line S1 and the second signal line S2 and the heating element H is less likely to occur than in the first embodiment.

[0066] [Configuration Example 2-2] FIG. 7 is a conceptual diagram showing an example of the configuration of a switching element (Configuration Example 2-2) according to the present disclosure. FIG. 7 is a cross-sectional view of the switching element taken along the line BB in FIG. 5. This configuration example differs from Configuration Example 2-1 in that a thermal conduction promotion layer 23 is disposed on the upper surface of the phase transition layer V. In the following, a description of the same configuration as Configuration Example 2-1 will be omitted.

[0067] The switching element 20-2 includes a substrate 21, a thermally conductive layer 22, a thermal conduction facilitating layer 23, a phase change layer V, a heating element H, an insulating layer 26, and an insulating layer 27. The insulating layer 27 is formed on the upper surface of the substrate 21. A through hole is formed in the insulating layer 27. The heating element H is embedded in the through hole formed in the insulating layer 27. The thermally conductive layer 22, the thermal conduction facilitating layer 23, and the phase change layer V are disposed above the insulating layer 27. The thermally conductive layer 22, the thermal conduction facilitating layer 23, and the phase change layer V are covered by the insulating layer 26. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 through the through hole formed in the insulating layer 27. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0068] The thermally conductive layer 22 is disposed on the upper surface of the insulating layer 27 in which the heating element H is embedded. The phase transition layer V is disposed on the upper surface of the thermally conductive layer 22. The thermally conductive layer 22 is made of a material having a higher thermal conductivity than the substrate 21, the insulating layer 27, and the phase transition layer V.

[0069] The phase change layer V is disposed on the upper surface of the thermal conduction layer 22. A thermal conduction promotion layer 23 is disposed on the upper surface of the phase change layer V. A heating element H is disposed below the phase change layer V with the thermal conduction layer 22 interposed therebetween. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when heated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection terminal C. The phase change layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch.

[0070] The thermal conduction promotion layer 23 has the same configuration as the thermal conduction promotion layer 13 of the first embodiment. The thermal conduction promotion layer 23 is disposed on the upper surface of the phase transition layer V. The upper surface of the thermal conduction promotion layer 23 is covered with an insulating layer 26. The thermal conduction promotion layer 23 is made of a material having a higher thermal conductivity than the phase transition layer V and the thermal conduction layer 22. That is, the thermal conduction promotion layer 23 has a higher thermal conductivity than the phase transition layer V and the thermal conduction layer 22.

[0071] When the heating element H generates heat in response to a selection made via the TFT circuit, the heat is conducted to the thermally conductive layer 22 disposed on the lower surface of the phase transition layer V. The heat conducted to the thermally conductive layer 22 is conducted within the thermally conductive layer 22 and then conducted to the phase transition layer V at the upper surface of the thermally conductive layer 22. The thermally conductive layer 22 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat from the heating element H is conducted to the vanadium dioxide contained in the phase transition layer V via the thermally conductive layer 22. The heat conducted to the upper surface of the phase transition layer V is conducted to the thermal conduction promotion layer 23. The thermal conduction promotion layer 23 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted in the thermal conduction promotion layer 23 is conducted to the phase transition layer V disposed on the lower surface. As a result, the phase transition layer V is uniformly heated via the thermal conduction promotion layer 23 disposed on the upper surface and the thermally conductive layer 22 disposed on the lower surface. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the connection terminal C. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 20-2 transitions to the ON state. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase. When the vanadium dioxide undergoes a phase transition to the insulating phase, the switching element 20-2 transitions to the OFF state.

[0072] In this configuration example, the phase transition layer V is sandwiched between the thermal conduction layer 22 and the thermal conduction promotion layer 23. In this configuration example, heat is conducted to the phase transition layer V via the thermal conduction layer 22 and the thermal conduction promotion layer 23, which have higher thermal conductivity than the phase transition layer V. In this configuration example, the phase transition layer V is sandwiched between the thermal conduction layer 22 and the thermal conduction promotion layer 23, which have higher thermal conductivity than the phase transition layer V. This makes it difficult for heat to escape to the substrate 21, and the phase transition layer V can be heated more efficiently than in configuration example 2-1. Furthermore, in this configuration example, because heat is difficult to escape to the substrate 21, the size of the heating element H can be made smaller than in configuration example 2-1. Therefore, in this configuration example, high-frequency coupling between the first signal line S1 and the second signal line S2 and the heating element H is less likely to occur than in configuration example 2-1.

[0073] In this configuration example, the thermal conduction facilitating layer 23 is disposed on the upper surface of the phase change layer V, and the thermally conductive layer 22 is disposed on the lower surface of the phase change layer V. For example, the thermally conductive layer 22 may be disposed on the upper surface of the phase change layer V, and the thermally conductive layer 23 may be disposed on the lower surface of the phase change layer V. For example, the thermally conductive layers 22 may be disposed on both surfaces of the phase change layer V. For example, the thermal conduction facilitating layer 23 may be disposed on both surfaces of the phase change layer V. For example, a thermally conductive structure including the thermally conductive layer 22 and the thermal conduction facilitating layer 23 may be disposed on the upper or lower surface of the phase change layer V.

[0074] As described above, the switching element of this embodiment includes a substrate, a phase change layer, a thermally conductive layer, and a heating element. The substrate is an insulator with lower thermal conductivity than the phase change layer and the thermally conductive layer. The phase change layer is made of a material that undergoes a metal-insulator phase transition. For example, the phase change layer contains vanadium dioxide as a material that undergoes a metal-insulator phase transition. The phase change layer is disposed on a signal line through which a signal to be transmitted or received propagates. The thermally conductive layer is an insulator with higher thermal conductivity than the phase change layer. The thermally conductive layer is formed between the substrate and the phase change layer. The heating element has a rectangular shape with long sides perpendicular to the extension direction of the signal line and short sides shorter than the sides of the phase change layer. The heating element is thermally connected to the phase change layer and the thermally conductive layer. The heating element is disposed below the phase change layer. For example, the heating element is embedded within the insulating layer.

[0075] The switching element of this embodiment includes a phase transition layer made of a material that undergoes a metal-insulator phase transition. A thermally conductive layer having a higher thermal conductivity than the phase transition layer is formed on the surface of the phase transition layer. The phase transition layer and the thermally conductive layer are thermally connected to a heating element. When the heating element generates heat, the phase transition layer is uniformly heated via the thermally conductive layer formed on the surface. Therefore, with the configuration of this embodiment, even if the heating element is reduced in size, the phase transition layer made of a material that undergoes a metal-insulator phase transition can be efficiently phase-transitioned. Furthermore, with the configuration of this embodiment, the signal line and the heating element are arranged separately, making it less likely for high-frequency coupling to occur between the signal line and the heating element.

[0076] In one aspect of this embodiment, the thermally conductive layer is disposed between the phase change layer and the heat generating element. In this aspect, heat conducted to the thermally conductive layer through the phase change layer is conducted in the thermally conductive layer faster than in the phase change layer. Because the heat conducted in the thermally conductive layer returns to the phase change layer, the phase change layer is easily heated uniformly. Therefore, this embodiment allows the phase change layer to undergo an efficient phase transition.

[0077] The switching element of one aspect of this embodiment includes a thermal conduction facilitating layer. The thermal conduction facilitating layer is an insulator with a higher thermal conductivity than the thermal conduction layer and is thermally connected to the phase change layer. For example, the thermal conduction facilitating layer is disposed on the upper surface of the phase change element. For example, the thermal conduction facilitating layer is disposed between the thermal conduction layer and the heat-generating element. According to this aspect, the thermal conduction facilitating layer, which has a higher thermal conductivity than the thermal conduction layer, allows the phase change of the phase change layer to occur more efficiently.

[0078] (Third embodiment) Next, a switching element according to a third embodiment will be described with reference to the drawings. The switching element according to this embodiment differs from the switching elements according to the first and second embodiments in the connection structure between the phase transition layer and the signal line. In the following, the description of the same configuration as the first or second embodiment will be simplified or omitted.

[0079] (composition) In the switching element of this embodiment, when the vanadium dioxide contained in the phase transition layer is formed, metallic vanadium is left at the connection portion with the first signal line and the second signal line. That is, the first signal line and the second signal line are electrically connected to the phase transition layer via metallic vanadium. In this embodiment, two configuration examples of the switching element are presented. Below, the configuration examples of the switching element are distinguished by adding a hyphen (-) and a number after the reference symbol.

[0080] [Configuration Example 3-1] 8 and 9 are conceptual diagrams showing an example of the configuration of a switching element (Configuration Example 3-1) according to the present disclosure. Configuration Example 3-1 is an example in which a heat generating element is disposed above a phase transition layer. A thermally conductive layer or a thermal conduction promotion layer may be disposed between the phase transition layer and the heat generating element. FIG. 8 is a plan view of the switching element viewed from above. FIG. 9 is a cross-sectional view of the switching element taken along the CC cutting line in FIG. 8.

[0081] The switching element 30-1 includes a substrate 31, a thermally conductive layer 32, a phase change layer V, a metal layer M, and a heating element H. The phase change layer V is disposed above the substrate 31. The thermally conductive layer 32 is disposed on the underside of the phase change layer V. Metal layers M are formed on the left and right ends of the phase change layer V. The metal layer M on the left side of the phase change layer V is covered by a first signal line S1. The metal layer M on the right side of the phase change layer V is covered by a second signal line S2. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. The heating element H is disposed on the top surface of the phase change layer V. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0082] The substrate 31 has the same configuration as the substrate 11 of the first embodiment. The substrate 31 is an insulator (dielectric). The substrate 31 has a lower thermal conductivity than the phase transition layer V. An insulating layer (not shown) may be formed on the upper surface of the substrate 31.

[0083] The thermally conductive layer 32 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 32 is disposed on the upper surface of the substrate 31. A phase transition layer V and a metal layer M are formed on the upper surface of the thermally conductive layer 32. The thermally conductive layer 32 is made of a material having a higher thermal conductivity than the substrate 31 and the phase transition layer V.

[0084] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. However, the phase change layer V differs from the phase change layer V in the first embodiment in that the phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. The phase change layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase change layer V is disposed on the upper surface of the thermally conductive layer 32. Heat from the heating element H is conducted to the phase change layer V via the thermally conductive layer 32. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when the heating element H generates heat.

[0085] The phase transition layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. The phase transition layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch. Vanadium dioxide is in an insulating phase below the phase transition temperature. Therefore, the switching element 30-1 is in an off state below the phase transition temperature. Vanadium dioxide is in a metallic phase above the phase transition temperature. Therefore, the switching element 30-1 is in an on state above the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0086] The metal layer M is formed on an end of the phase transition layer V. The metal layer M is formed on the upper surface of the thermally conductive layer 32. The metal layer M is formed between the first signal line S1 and the thermally conductive layer 32, and between the second signal line S2 and the thermally conductive layer 32. The metal layer M is electrically connected to the first signal line S1 and the second signal line S2. Heat from the heating element H is conducted to the metal layer M via the thermally conductive layer 32 and the phase transition layer V.

[0087] Here, a method for forming the phase transition layer V and the metal layer M will be described. First, a thermally conductive layer 32 is formed on the upper surface of the substrate 31. For example, the thermally conductive layer 32 is a thin film layer of α-alumina. After the thermally conductive layer 32 is formed on the upper surface of the substrate 31, metal vanadium is deposited on the upper surface of the thermally conductive layer 32. For example, the metal vanadium is deposited on the upper surface of the thermally conductive layer 32 using a technique such as sputtering. Then, the thermally conductive layer 32 and the metal vanadium are patterned to have the same shape. The upper ends of the metal vanadium and the side surfaces of the thermally conductive layer 32 and the metal vanadium are covered with metal electrodes (the first signal line S1 and the second signal line S2). Then, annealing is performed in an oxidizing atmosphere. According to this procedure, the metal vanadium in the portions not covered with the metal electrodes (the first signal line S1 and the second signal line S2) is oxidized to form vanadium dioxide (the phase transition layer V). On the other hand, the portions covered with the metal electrodes (the first signal line S1 and the second signal line S2) remain as the metal layer M. As a result, the phase transition layer V and the metal layer M are seamlessly connected. Note that the method for forming the phase transition layer V and the metal layer M described above is merely an example and does not limit the methods for forming the phase transition layer V and the metal layer M in this embodiment. For example, the phase transition layer V may be formed by implanting oxygen ions into metallic vanadium using an ion implantation technique.

[0088] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is disposed on the upper surface of the phase transition layer V. The heating element H has an elongated rectangular shape extending perpendicular to the extension direction of the first signal line S1 and the second signal line S2. That is, the heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the phase transition layer V disposed on the lower surface of the heating element H. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0089] When the heating element H generates heat in response to a selection made via the TFT circuit, the heat is conducted to the phase transition layer V. The heat conducted to the phase transition layer V is then conducted to the thermally conductive layer 32 disposed below the phase transition layer V. The thermally conductive layer 32 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted in the thermally conductive layer 32 is then conducted to the phase transition layer V disposed above it. As a result, the phase transition layer V is uniformly heated via the thermally conductive layer 32 disposed below it. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide transitions to the metallic phase, the switching element 30-1 transitions to the on state. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the metal layer M. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase, and the switching element 30-1 transitions to the off state.

[0090] The metal vanadium constituting the metal layer M has a lower thermal conductivity than the metal constituting the first signal line S1 and the second signal line S2. Therefore, compared to the first and second embodiments, in this configuration example, heat conducted in the thermal conduction layer 32 is less likely to be conducted to the signal lines (the first signal line S1 and the second signal line S2). Furthermore, because the metal layer M and the phase change layer V are formed without discontinuities, electricity is conducted efficiently when the phase change layer V undergoes a phase transition to a metallic phase. Metal vanadium has a lower electrical conductivity than copper and aluminum, but a higher electrical conductivity than vanadium dioxide. Therefore, compared to the first and second embodiments, this configuration example has a lower resistance between the first signal line S1 and the second signal line S2 and the phase change layer V via the metal layer M. In this configuration example, the area of ​​contact between the metal layer M and the phase change layer V is significantly smaller than the area of ​​contact between the phase change layer V and the signal layer in the first and second embodiments. Therefore, in this configuration example, the temperature rise of the metal layer M can be suppressed, and the contact resistance at the contact portion between the metal layer M and the phase transition layer V can be reduced.

[0091] [Configuration Example 3-2] 10 and 11 are conceptual diagrams showing an example of the configuration of a switching element (Configuration Example 3-2) according to the present disclosure. Configuration Example 3-2 is an example in which a heat generating element is disposed below a phase transition layer. FIG. 10 is a plan view of the switching element viewed from above. FIG. 11 is a cross-sectional view of the switching element cut along the cutting line DD in FIG. 10. In the following, descriptions of configurations similar to Configuration Example 3-1 will be omitted.

[0092] The switching element 30-2 includes a substrate 31, a thermally conductive layer 32, a phase change layer V, a metal layer M, a heating element H, and an insulating layer 37. The phase change layer V is disposed on the upper surface of the insulating layer 37. The thermally conductive layer 32 is disposed on the lower surface of the phase change layer V. The left end of the phase change layer V is covered by a first signal line S1. The right end of the phase change layer V is covered by a second signal line S2. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. The formation region of the phase change layer V, which is covered by the first signal line S1 and the second signal line S2, is indicated by a dashed line. The portion covered by the first signal line S1 and the second signal line S2 is the metal layer M. The heating element H is disposed below the phase change layer V. The heating element H is disposed on the lower surface of the thermally conductive layer 32. The formation region of the heating element H is indicated by a dashed line. The phase transition layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0093] The substrate 31 has the same configuration as the substrate 11 of the first embodiment. The substrate 31 is an insulator (dielectric). The substrate 31 has a lower thermal conductivity than the phase transition layer V. An insulating layer (not shown) may be formed on the upper surface of the substrate 31.

[0094] The thermally conductive layer 32 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 32 is disposed on the upper surface of the substrate 31. A phase transition layer V and a metal layer M are disposed on the upper surface of the thermally conductive layer 32. The thermally conductive layer 32 is made of a material having a higher thermal conductivity than the substrate 31 and the phase transition layer V.

[0095] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V differs from the phase change layer V in the second embodiment in that the phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. The phase change layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase change layer V is disposed on the upper surface of the thermally conductive layer 32. Heat from the heating element H is conducted to the phase change layer V via the thermally conductive layer 32. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when the heating element H generates heat.

[0096] The phase transition layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M. The phase transition layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch. Vanadium dioxide is in an insulating phase below the phase transition temperature. Therefore, the switching element 30-2 is in an off state below the phase transition temperature. Vanadium dioxide is in a metallic phase above the phase transition temperature. Therefore, the switching element 30-2 is in an on state above the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0097] The metal layer M is connected to an end of the phase transition layer V. The metal layer M is disposed on the upper surface of the thermally conductive layer 32. The metal layer M is formed between the first signal line S1 and the thermally conductive layer 32 and between the second signal line S2 and the thermally conductive layer 32. The metal layer M is electrically connected to the first signal line S1 and the second signal line S2. Heat from the heating element H is conducted to the metal layer M via the thermally conductive layer 32 and the phase transition layer V. The metal layer M can be formed in the same manner as in configuration example 3-1.

[0098] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is disposed on the lower surface of the thermally conductive layer 32. The heating element H has an elongated rectangular shape extending perpendicular to the direction in which the first signal line S1 and the second signal line S2 extend. That is, the heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the thermally conductive layer 32 disposed on the upper surface of the heating element H. The heat conducted to the thermally conductive layer 32 is conducted inside the thermally conductive layer 32 and conducted to the phase transition layer V disposed on the upper surface thereof. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, in consideration of the hysteresis characteristic, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0099] The insulating layer 37 is formed on the upper surface of the substrate 31. The heating element H is embedded in the insulating layer 37. For example, the insulating layer 37 is made of an insulating material such as silicon dioxide. If the surface of the phase transition layer V formed on the insulating layer 27 is uneven, these unevenness may become singular points and cause signal reflection. For this reason, the upper surface of the insulating layer 37 is planarized. For example, the upper surface of the insulating layer 37 is planarized using a technique such as chemical mechanical polishing (CMP). The thermal conductivity of the insulating layer 37 is similar to that of the substrate 31. That is, the thermal conductivity of the insulating layer 37 is lower than that of the phase transition layer V.

[0100] When the heating element H generates heat in response to selection via the TFT circuit, the heat is conducted to the thermally conductive layer 32 disposed on the upper surface of the heating element H. The heat conducted to the thermally conductive layer 32 is then conducted to the phase transition layer V disposed on the upper surface. The thermally conductive layer 32 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. As a result, the phase transition layer V is uniformly heated via the thermally conductive layer 32 disposed on the lower surface. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2 via the metal layer M. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 30-2 transitions to the on state. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase. When the vanadium dioxide undergoes a phase transition to the insulating phase, the switching element 30-2 transitions to the OFF state.

[0101] The metallic vanadium constituting the metal layer M has a lower thermal conductivity than the metal constituting the first signal line S1 and the second signal line S2. Therefore, compared to the second embodiment, in this configuration example, heat conducted in the thermal conduction layer 32 is less likely to be conducted to the first signal line S1 and the second signal line S2. Furthermore, because the metal layer M and the phase change layer V are formed without discontinuities, electricity is efficiently conducted when the phase change layer V undergoes a phase transition to a metallic phase. Metal vanadium has a lower electrical conductivity than copper and aluminum, but a higher electrical conductivity than vanadium dioxide. Therefore, compared to the first and second embodiments, this configuration example has a lower resistance between the first and second signal lines S1 and S2 and the phase change layer V via the metal layer M. In this configuration example, the area of ​​contact between the metal layer M and the phase change layer V is significantly smaller than the area of ​​contact between the phase change layer V and the signal layer in the first and second embodiments. Therefore, in this configuration example, it is possible to suppress a temperature rise in the metal layer M, thereby reducing the contact resistance at the contact portion between the metal layer M and the phase transition layer V. Furthermore, according to this configuration example, the signal lines (first signal line S1 and second signal line S2) and the heat-generating element H are arranged separately, so high-frequency coupling between the signal lines and the heat-generating element is unlikely to occur.

[0102] As described above, the switching element of this embodiment includes a substrate, a phase change layer, a thermally conductive layer, and a heating element. The substrate is an insulator with lower thermal conductivity than the phase change layer and the thermally conductive layer. The phase change layer is made of a material that undergoes a metal-insulator phase transition. For example, the phase change layer contains vanadium dioxide as a material that undergoes a metal-insulator phase transition. The phase change layer is disposed on a signal line through which a signal to be transmitted or received propagates. The phase change layer is connected to the signal line via the vanadium metal. The thermally conductive layer is an insulator with higher thermal conductivity than the phase change layer. The thermally conductive layer is formed between the substrate and the phase change layer. The heating element is rectangular, with long sides perpendicular to the extension direction of the signal line and short sides shorter than the sides of the phase change layer. The heating element is thermally connected to the phase change layer and the thermally conductive layer. The heating element is disposed above or below the phase change layer.

[0103] In the switching element of this embodiment, the phase transition layer and the signal line are in contact with each other via metallic vanadium. Compared to the material constituting the signal line, metallic vanadium has a lower thermal conductivity. Therefore, according to this embodiment, heat is less likely to escape from the phase transition layer to the signal line, improving the efficiency of heating by the heating element.

[0104] (Fourth embodiment) Next, a switching element according to a fourth embodiment will be described with reference to the drawings. The switching element according to this embodiment differs from the switching elements according to the first to third embodiments in that the phase-change element and the heat-generating element are arranged so as not to overlap each other in a plan view. In the following, the description of the same configuration as in the first to third embodiments will be simplified or omitted.

[0105] (composition) In the switching element of this embodiment, the phase change element and the heat generating element do not overlap in a planar view. The phase change element and the heat generating element are thermally connected via a thermal conduction layer or a thermal conduction promotion layer formed on the surface of the substrate. In this embodiment, four configuration examples of the switching element are presented. In the following, the configuration examples of the switching element are distinguished by adding a hyphen (-) and a number after the reference symbol.

[0106] [Configuration Example 4-1] 12 and 13 are conceptual diagrams showing an example of the configuration of a switching element (Configuration Example 4-1) in the present disclosure. Configuration Example 4-1 is an example in which a heat generating element and a heat generating element are arranged on the upper surface of a thermally conductive layer. FIG. 12 is a plan view of the switching element viewed from above. FIG. 13 is a cross-sectional view of the switching element taken along the E-E cutting line in FIG. 12.

[0107] The switching element 40-1 includes a substrate 41, a thermally conductive layer 42, a phase change layer V, and a heating element H. The phase change layer V and the heating element H are disposed on the upper surface of the thermally conductive layer 42. An insulating layer (not shown) may be formed above the thermally conductive layer 42, the phase change layer V, and the heating element H. The thermally conductive layer 42 is disposed on the upper surface of the substrate 41. The phase change layer V is electrically connected to a first signal line S1 and a second signal line S2 via a connection terminal C. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0108] The substrate 41 has the same structure as the substrate 11 of the first embodiment. The substrate 41 is an insulator (dielectric). The substrate 41 has a lower thermal conductivity than the phase transition layer V.

[0109] The thermally conductive layer 42 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 42 is disposed on the upper surface of the substrate 41. The phase transition layer V and the heat generating element H are disposed on the upper surface of the thermally conductive layer 42. The thermally conductive layer 42 is made of a material having a higher thermal conductivity than the substrate 41 and the phase transition layer V.

[0110] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V is disposed on the upper surface of the thermally conductive layer 42. Heat from the heating element H is conducted to the phase change layer V via the thermally conductive layer 42. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase in response to heat generated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2.

[0111] The phase transition layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase transition layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch. At temperatures lower than the phase transition temperature, vanadium dioxide is in the insulating phase. Therefore, the switching element 40-1 is in the OFF state at temperatures lower than the phase transition temperature. At temperatures higher than the phase transition temperature, vanadium dioxide is in the metallic phase. Therefore, the switching element 40-1 is in the ON state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0112] The heating element H has the same configuration as the heating element H in the first embodiment. The phase change layer V and the heating element H are arranged on the same side of the substrate 41. The heating element H is arranged on the same side as the thermally conductive layer 42. The heating element H is arranged on the same surface as the phase change layer V on the upper surface of the thermally conductive layer 42. The heating element H is arranged at a distance from the phase change layer V. The heating element H is thermally connected to the phase change layer V via the thermally conductive layer 42. The heating element H has an elongated rectangular shape extending in the direction in which the first signal line S1 and the second signal line S2 extend. The heating element H is smaller than the phase change layer V.

[0113] The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the phase transition layer V via a thermal conduction layer 42 disposed on the underside of the heating element H. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0114] When the heating element H generates heat in response to selection via the TFT circuit, the heat is conducted to the thermally conductive layer 42. The thermally conductive layer 42 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted by the thermally conductive layer 42 is conducted to the phase transition layer V disposed on the upper surface. As a result, the phase transition layer V is uniformly heated via the thermally conductive layer 42 disposed on the lower surface. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 40-1 transitions to the on state. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase. When the vanadium dioxide undergoes a phase transition to the insulating phase, the switching element 40-1 transitions to the OFF state.

[0115] In this configuration example, the phase transition layer V and the heating element H are arranged on the same side of the substrate 41. This configuration example increases the degree of freedom in determining the positional relationship between the phase transition layer V and the heating element H.

[0116] [Configuration Example 4-2] 14 and 15 are conceptual diagrams showing an example of the configuration of a switching element (Configuration Example 4-2) according to the present disclosure. Configuration Example 4-2 is an example in which a thermal conduction layer and a heat generating element are disposed on the upper surface of a thermal conduction promotion layer, and a thermal conduction layer is disposed on the upper surface of the thermal conduction layer. FIG. 14 is a plan view of the switching element viewed from above. FIG. 15 is a cross-sectional view of the switching element taken along the FF cutting line in FIG. 14.

[0117] The switching element 40-2 includes a substrate 41, a thermally conductive layer 42, a thermal conduction promotion layer 43, a phase change layer V, and a heat-generating element H. The phase change layer V and the heat-generating element H are disposed on the upper surface of the thermal conduction promotion layer 43. An insulating layer (not shown) may be formed above the thermally conductive layer 42, the thermal conduction promotion layer 43, the phase change layer V, and the heat-generating element H. A thermally conductive layer is disposed on the lower surface of the thermal conduction promotion layer 43. The thermal conduction layer 42 is disposed on the upper surface of the substrate 41. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection terminal C. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0118] The substrate 41 has the same structure as the substrate 11 of the first embodiment. The substrate 41 is an insulator (dielectric). The substrate 41 has a lower thermal conductivity than the phase transition layer V.

[0119] The thermal conduction layer 42 has the same configuration as the thermal conduction layer 12 of the first embodiment. The thermal conduction layer 42 is disposed on the upper surface of the thermal conduction promotion layer 43. The phase transition layer V and the heat-generating element H are disposed on the upper surface of the thermal conduction layer 42. The thermal conduction layer 42 is made of a material having a higher thermal conductivity than the substrate 41 and the phase transition layer V, but a lower thermal conductivity than the thermal conduction promotion layer 43.

[0120] The thermal conduction promotion layer 43 has the same configuration as the thermal conduction promotion layer 13 of the first embodiment. The thermal conduction promotion layer 43 is disposed on the upper surface of the substrate 41. The thermal conduction layer 42 and the heat generating element H are disposed on the upper surface of the thermal conduction promotion layer 43. The thermal conduction promotion layer 43 is made of a material having a higher thermal conductivity than the substrate 41 and the thermal conduction layer 42.

[0121] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V is disposed on the upper surface of the thermally conductive layer 42. Heat from the heating element H is conducted to the phase change layer V via the thermally conductive layer 42. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase in response to heat generated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2.

[0122] The phase transition layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase transition layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch. At temperatures lower than the phase transition temperature, vanadium dioxide is in the insulating phase. Therefore, the switching element 40-2 is in the off state at temperatures lower than the phase transition temperature. At temperatures higher than the phase transition temperature, vanadium dioxide is in the metallic phase. Therefore, the switching element 40-2 is in the on state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0123] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is arranged on the upper surface of the thermal conduction promotion layer 43. The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is arranged on the upper surface of the thermal conduction promotion layer 43. The heating element H is arranged on the same plane as the thermal conduction layer 42, on the upper surface of the thermal conduction layer 42. The heating element H is arranged at a distance from the thermal conduction layer 42. The heating element H is thermally connected to the phase transition layer V via the thermal conduction layer 42 and the thermal conduction promotion layer 43. The heating element H has an elongated rectangular shape extending along the extension direction of the first signal line S1 and the second signal line S2. The heating element H is smaller than the phase transition layer V.

[0124] The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat of the heating element H is conducted to the thermal conduction layer 42 via the thermal conduction promotion layer 43 disposed on the lower surface of the heating element H. The heat conducted to the thermal conduction layer 42 is then conducted to the phase transition layer V via the thermal conduction layer 42. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0125] When the heating element H generates heat in response to a selection via the TFT circuit, the heat is conducted to the thermal conduction promotion layer 43. The heat conducted to the thermal conduction promotion layer 43 is then conducted in the thermal conduction promotion layer 43 and then to the thermal conduction layer 42 disposed on the upper surface. The thermal conduction layer 42 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted in the thermal conduction layer 42 is conducted to the phase transition layer V disposed on the upper surface. As a result, the phase transition layer V is uniformly heated via the thermal conduction layer 42 disposed on the lower surface. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 40-2 transitions to the on state. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase, and the switching element 40-2 transitions to the off state.

[0126] In this configuration example, the phase transition layer V and the heating element H are arranged on the same side of the substrate 41. In addition, in this configuration example, heat from the heating element H is conducted to the phase transition layer V via the thermal conduction promotion layer 43, which has a higher thermal conductivity than the thermal conduction layer 42. Therefore, according to this configuration example, the phase transition layer V can be heated more efficiently than in configuration example 4-1.

[0127] [Configuration Example 4-3] 16 and 17 are conceptual diagrams showing an example of the configuration of a switching element (Configuration Example 4-3) in the present disclosure. Configuration Example 4-3 is an example in which a heat generating element and a heat generating element are arranged on the upper surface of a thermal conduction layer, and the surfaces thereof are covered with a thermal conduction promotion layer. FIG. 16 is a plan view of the switching element viewed from above. FIG. 17 is a cross-sectional view of the switching element taken along the line GG in FIG. 16.

[0128] The switching element 40-3 includes a substrate 41, a thermally conductive layer 42, a thermal conduction promotion layer 44, a phase change layer V, and a heat-generating element H. The upper surfaces of the phase change layer V and the heat-generating element H are covered with the thermal conduction promotion layer 44. The thermally conductive layer 42 is disposed below the thermal conduction promotion layer 44. The thermally conductive layer 42 is disposed on the upper surface of the substrate 41. An insulating layer (not shown) may be formed above the thermally conductive layer 42, the thermal conduction promotion layer 44, the phase change layer V, and the heat-generating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via a connection end C. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0129] The substrate 41 has the same structure as the substrate 11 of the first embodiment. The substrate 41 is an insulator (dielectric). The substrate 41 has a lower thermal conductivity than the phase transition layer V.

[0130] The thermally conductive layer 42 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 42 is disposed on the upper surface of the substrate 41. The phase transition layer V and the heat-generating element H are disposed on the upper surface of the thermally conductive layer 42. The thermally conductive layer 42 is covered from above with a thermal conduction promotion layer 44. The thermally conductive layer 42 is made of a material having a higher thermal conductivity than the substrate 41 and the phase transition layer V, but a lower thermal conductivity than the thermal conduction promotion layer 44.

[0131] The thermal conduction promotion layer 44 covers the upper surfaces of the thermal conduction layer 42, the phase transition layer V, and the heat-generating element H. The thermal conduction promotion layer 44 is made of a material with a higher thermal conductivity than the substrate 41, the thermal conduction layer 42, and the phase transition layer V. There are no limitations on the material of the thermal conduction promotion layer 44 as long as it is made of a material with a higher thermal conductivity than the substrate 41, the thermal conduction layer 42, and the phase transition layer V. For example, the thermal conduction promotion layer 44 is made of silicon carbide. Silicon carbide has a crystal system whose thermal conductivity is comparable to that of metals.

[0132] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V is disposed on the upper surface of the thermally conductive layer 42. Heat from the heating element H is conducted to the phase change layer V via the thermally conductive layer 42. The phase change layer V is also covered with a thermal conduction promotion layer 44. Heat from the heating element H is conducted to the phase change layer V via the thermal conduction promotion layer 44. That is, heat is conducted to the phase change layer V from the thermally conductive layer 42 on the lower surface and from the thermal conduction promotion layer 44 on the upper surface. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when heated by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M.

[0133] The phase transition layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase transition layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch. At temperatures lower than the phase transition temperature, vanadium dioxide is in the insulating phase. Therefore, the switching element 40-3 is in the OFF state at temperatures lower than the phase transition temperature. At temperatures higher than the phase transition temperature, vanadium dioxide is in the metallic phase. Therefore, the switching element 40-3 is in the ON state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0134] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is disposed on the upper surface of the thermally conductive layer 42. The heating element H is disposed on the same surface as the phase change layer V on the upper surface of the thermally conductive layer 42. The heating element H is disposed at a distance from the phase change layer V. The heating element H is thermally connected to the phase change layer V via the thermally conductive layer 42 and the thermal conduction promotion layer 44. The heating element H is also covered by the thermal conduction promotion layer 44. The heating element H is thermally connected to the phase change layer V via the thermally conductive layer 42 and the thermal conduction promotion layer 44. The heating element H has an elongated rectangular shape extending in the direction in which the first signal line S1 and the second signal line S2 extend. The heating element H is smaller than the phase change layer V.

[0135] The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the phase transition layer V via the thermal conduction layer 42 and the thermal conduction promotion layer 44. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0136] When the heating element H generates heat in response to selection via the TFT circuit, the heat is conducted to the thermal conductive layer 42 and the thermal conduction promotion layer 44. The heat conducted to the thermal conductive layer 42 is conducted within the thermal conductive layer 42 and then to the phase transition layer V disposed on the upper surface. The thermal conductive layer 42 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. The heat conducted to the thermal conduction promotion layer 44 is conducted within the thermal conduction promotion layer 44 and then to the phase transition layer V disposed below. The thermal conduction promotion layer 44 has a higher thermal conductivity than the phase transition layer V, and therefore conducts heat more efficiently than the phase transition layer V. As a result, the phase transition layer V is efficiently heated via the thermal conductive layer 42 disposed on the lower surface and the thermal conduction promotion layer 44 covering the upper surface. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from an insulating phase to a metallic phase. When the vanadium dioxide undergoes a phase transition to the metallic phase, the switching element 40-3 transitions to the ON state. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide transitions from the metallic phase to the insulating phase. When the vanadium dioxide transitions to the insulating phase, the switching element 40-3 transitions to the OFF state.

[0137] In this configuration example, the phase change layer V and the heat generating element H are arranged on the same side of the substrate 41. In addition, in this configuration example, the phase change layer V is sandwiched between the thermal conduction layer 42 and the thermal conduction promotion layer 44. Therefore, according to this configuration example, the phase change layer V can be heated more efficiently than in Configuration Examples 4-1 and 4-2.

[0138] [Configuration Example 4-4] 18 and 19 are conceptual diagrams showing an example of the configuration of a switching element (Configuration Example 4-4) in the present disclosure. Configuration Example 4-4 is an example in which a heat generating element is arranged on the upper surface of a thermal conduction layer, the surfaces of which are covered with a thermal conduction promotion layer, and the heat generating element is arranged on the upper surface of the thermal conduction promotion layer. FIG. 18 is a plan view of the switching element viewed from above. FIG. 19 is a cross-sectional view of the switching element taken along the HH cutting line in FIG. 18.

[0139] The switching element 40-4 includes a substrate 41, a thermally conductive layer 42, a thermal conduction promotion layer 44, a phase change layer V, and a heating element H. The phase change layer V is disposed on the lower surface of the thermal conduction promotion layer 44. When viewed from above, the heating element H is disposed on the upper surface of the thermal conduction promotion layer 44. The thermally conductive layer 42 is disposed below the thermal conduction promotion layer 44. The thermally conductive layer 42 is disposed on the upper surface of the substrate 41. An insulating layer (not shown) may be formed above the thermally conductive layer 42, the thermal conduction promotion layer 44, the phase change layer V, and the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the connection terminal C. The heating element H is disposed above the phase change layer V in the drawing. For example, the first signal line S1 and the second signal line S2 are made of a metal such as copper or aluminum.

[0140] The substrate 41 has the same structure as the substrate 11 of the first embodiment. The substrate 41 is an insulator (dielectric). The substrate 41 has a lower thermal conductivity than the phase transition layer V.

[0141] The thermally conductive layer 42 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 42 is disposed on the upper surface of the substrate 41. A phase transition layer V is disposed on the upper surface of the thermally conductive layer 42. The thermally conductive layer 42 is made of a material having a higher thermal conductivity than the substrate 41 and the phase transition layer V, but a lower thermal conductivity than the thermal conduction promotion layer 44.

[0142] The thermal conduction promotion layer 44 has the same configuration as the thermal conduction promotion layer 44 in Configuration Example 4-3. The thermal conduction promotion layer 44 covers the upper surfaces of the thermal conduction layer 42 and the phase transition layer V. The thermal conduction promotion layer 44 is made of a material having a higher thermal conductivity than the substrate 41, the thermal conduction layer 42, and the phase transition layer V.

[0143] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V is disposed on the upper surface of the thermally conductive layer 42. Heat from the heating element H is conducted to the phase change layer V via the thermally conductive layer 42. The phase change layer V is also covered with a thermal conduction promotion layer 44. Heat from the heating element H is conducted to the phase change layer V via the thermal conduction promotion layer 44. That is, heat is conducted to the phase change layer V from the thermally conductive layer 42 on the lower surface and from the thermal conduction promotion layer 44 on the upper surface. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase when the heating element H generates heat. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2 via the metal layer M.

[0144] The phase transition layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase transition layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch. At temperatures lower than the phase transition temperature, vanadium dioxide is in the insulating phase. Therefore, the switching element 40-4 is in the off state at temperatures lower than the phase transition temperature. At temperatures higher than the phase transition temperature, vanadium dioxide is in the metallic phase. Therefore, the switching element 40-4 is in the on state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0145] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is disposed on the upper surface of the thermal conduction promotion layer 44. The heating element H is disposed on the same side as the phase change layer V with respect to the upper surface of the thermal conduction layer 42. The heating element H is disposed at a distance from the phase change layer V. The heating element H is thermally connected to the phase change layer V via the thermal conduction layer 42 and the thermal conduction promotion layer 44. The heating element H has an elongated rectangular shape extending along the extension direction of the first signal line S1 and the second signal line S2. The heating element H is smaller than the phase change layer V.

[0146] The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit connected to the heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the thermal conduction layer 42 and the phase transition layer V via the thermal conduction promotion layer 44. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0147] When the heating element H generates heat in response to a selection via the TFT circuit, the heat is conducted to the thermal conduction promotion layer 44. The heat conducted to the thermal conduction promotion layer 44 is then conducted through the thermal conduction promotion layer 44 to the phase transition layer V and the thermal conductive layer 42 disposed on the lower surface. The thermal conductive layer 42 and the thermal conduction promotion layer 44 have higher thermal conductivities than the phase transition layer V, and therefore conduct heat more efficiently than the phase transition layer V. As a result, the phase transition layer V is efficiently heated via the thermal conductive layer 42 disposed on the lower surface and the thermal conduction promotion layer 44 covering the upper surface. When the temperature of the vanadium dioxide exceeds the phase transition temperature, the vanadium dioxide undergoes a phase transition from the insulating phase to the metallic phase. When the vanadium dioxide transitions to the metallic phase, the switching element 40-4 transitions to the on state. The heat conducted to the phase transition layer V is also conducted to the first signal line S1 and the second signal line S2. When the deselected heating element H stops generating heat and the temperature of the vanadium dioxide falls below the phase transition temperature, the vanadium dioxide undergoes a phase transition from the metallic phase to the insulating phase, and the switching element 40-4 transitions to the off state.

[0148] In this configuration example, the phase transition layer V and the heating element H are arranged on the same side of the substrate 41. In addition, in this configuration example, the phase transition layer V is sandwiched between the thermal conduction layer 42 and the thermal conduction promotion layer 44. Therefore, according to this configuration example, the phase transition layer V can be efficiently heated, similar to configuration example 4-3.

[0149] As described above, the switching element of this embodiment includes a substrate, a phase change layer, a thermally conductive layer, and a heating element. The substrate is an insulator with lower thermal conductivity than the phase change layer and the thermally conductive layer. The phase change layer is made of a material that undergoes a metal-insulator phase transition. For example, the phase change layer contains vanadium dioxide as a material that undergoes a metal-insulator phase transition. The phase change layer is disposed on a signal line through which a signal to be transmitted or received propagates. The portion of the phase change layer connected to the signal line is metallic vanadium. The thermally conductive layer is an insulator with higher thermal conductivity than the phase change layer. The thermally conductive layer is formed between the substrate and the phase change layer. The heating element is rectangular, with long sides perpendicular to the extension direction of the signal line and short sides shorter than the sides of the phase change layer. The heating element is thermally connected to the phase change layer and the thermally conductive layer. The phase change layer and the heating element are disposed on the same surface of the thermally conductive layer, spaced apart from each other.

[0150] In the switching element of this embodiment, the phase change layer and the heating element are arranged on the same surface of the thermally conductive layer with a gap between them. Heat from the heating element is conducted to the phase change layer via the thermally conductive layer. According to this embodiment, the phase change layer and the heating element can be arranged on the same side of the substrate on which the thermally conductive layer is formed, due to the heat conduction via the thermally conductive layer.

[0151] In one aspect of this embodiment, at least one of the phase change layer, the heat generating element, and the thermally conductive layer is covered with a thermal conduction facilitating layer, which is an insulator having a higher thermal conductivity than the thermally conductive layer. For example, the phase change layer, the heat generating element, and the thermally conductive layer are covered with the thermal conduction facilitating layer. For example, the phase change layer and the thermally conductive layer are covered with the thermal conduction facilitating layer, and the heat generating element is disposed on the upper surface of the thermal conduction facilitating layer. According to this aspect, the use of the thermal conduction facilitating layer allows the phase change phase to be transitioned more efficiently.

[0152] The switching element of one aspect of this embodiment includes a thermal conduction facilitating layer, which is an insulator having a higher thermal conductivity than the thermal conduction layer and is thermally connected to the phase transition layer. The phase transition layer and the heat generating element are disposed on the same side of the thermal conduction facilitating layer with a gap therebetween. For example, the thermal conduction layer is disposed between the phase transition layer and the thermal conduction facilitating layer. According to this aspect, the use of the thermal conduction facilitating layer allows the phase transition phase to be more efficiently transitioned.

[0153] (Fifth embodiment) Next, a phase shifter according to a fifth embodiment will be described with reference to the drawings. For example, the phase shifter according to this embodiment is mounted on a planar antenna including a plurality of patch antennas. If a planar antenna including the phase shifter according to this embodiment is realized, a phased array antenna that transmits directional radio waves can be configured. Such a planar antenna is used for transmitting and receiving electromagnetic waves in a high frequency band that is expected to be applied to B5G (Beyond 5th Generation) mobile communications following 5G (5th Generation). Note that the switching element according to this embodiment can be mounted on any device, not just a planar antenna.

[0154] (composition) The phase shifter of this embodiment has a structure in which the switching elements of the first to fourth embodiments are connected together. For example, the switching elements of the first to fourth embodiments are applied to an extension structure used to extend the signal lines of the phase shifter. In this embodiment, two configuration examples of the extension structure of the phase shifter are given. In the following, the configuration examples of the extension structure of the phase shifter are distinguished by adding a hyphen (-) and a number after the reference symbol.

[0155] For example, the phase shifter is a variable line length phase shifter in which multiple phase shift wirings with different line lengths branch off from a main wiring in a side chain configuration. For example, the phase shift wirings are stubs with open ends. Openable and closable selection switches (not shown) are disposed at the contact points between the multiple phase shift wirings and the main wiring. The phase shift wirings are selected depending on whether the selection switches disposed at the contact points with the main wiring are open or closed. The selection switches may be configured as phase transition switches.

[0156] [Configuration Example 5-1] 20 to 22 are conceptual diagrams showing an example of an extended structure (Configuration Example 5-1) of a phase shifter according to the present disclosure. Configuration Example 5-1 is an example in which heat conduction layers included in a plurality of switching elements are not divided for each element. FIG. 20 is a plan view looking down on a portion of a phase shifter (phase shift wiring) from an upper viewpoint. FIG. 21 is a cross-sectional view taken along line II in FIG. 20. FIG. 22 is a cross-sectional view taken along line JJ in FIG. 20. FIGS. 20 to 22 show a portion of a phase shift wiring whose line length can be extended depending on the selection of a heat generating element.

[0157] The phase-shifting wiring 50-1 includes a substrate 51, a thermally conductive layer 52, a phase transition layer V, and a plurality of heating elements H. A single switching element is formed by two heating elements H facing each other in a direction perpendicular to the extending direction of the phase-shifting wiring 50-1 and a portion of the phase transition layer V that undergoes a phase transition to a metallic phase in response to heat generation by the heating elements H. The two heating elements H facing each other in a direction perpendicular to the extending direction of the phase-shifting wiring 50-1 form a heating element pair. Signal lines and other wiring are omitted in FIGS. 20 to 22.

[0158] The substrate 51 has the same configuration as the substrate 11 of the first embodiment. The substrate 51 is an insulator (dielectric). The substrate 51 has a lower thermal conductivity than the phase transition layer V. The substrate 51 extends along the extension direction of the phase shift wiring 50-1.

[0159] The thermally conductive layer 52 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 52 is disposed on the upper surface of the substrate 51. A phase transition layer V is disposed on the upper surface of the thermally conductive layer 52. The thermally conductive layer 52 is made of a material having a higher thermal conductivity than the substrate 51 and the phase transition layer V. The thermally conductive layer 52 may be combined with a thermal conduction promotion layer. The thermally conductive layer 52 extends on the upper surface of the substrate 51 along the extension direction of the phase-shifting wiring 50-1.

[0160] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V differs from the phase change layer V in the first embodiment in that the phase change layer V extends on the upper surface of the thermally conductive layer 52 along the extension direction of the phase-shifting wiring 50-1. The phase change layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase change layer V is disposed on the upper surface of the thermally conductive layer 52. The phase change layer V extends on the upper surface of the substrate 51 along the extension direction of the phase-shifting wiring 50-1. Heat from the two heating elements H constituting the heating element pair is conducted to the phase change layer V via the thermally conductive layer 52. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase due to heat generated by the two heating elements H constituting the heating element pair.

[0161] At temperatures lower than the phase transition temperature, vanadium dioxide is in an insulating phase. Therefore, the switching element is in an off state at temperatures lower than the phase transition temperature. At temperatures higher than the phase transition temperature, vanadium dioxide is in a metallic phase. Therefore, the switching element is in an on state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0162] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is disposed on the upper surface of the thermally conductive layer 52. The heating element H and the phase transition layer V are disposed above the substrate 51. The heating element H is disposed at a distance from the phase transition layer V. The heating element H has an elongated rectangular shape extending perpendicular to the extension direction of the phase shift wiring 50-1. The heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit (not shown) constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. Two heating elements H constituting a heating element pair are connected to the same drive circuit. When the drive circuit connected to the two heating elements H in a pair is selected, the heating elements H generate heat. Heat from the heating element H is conducted to the phase transition layer V via the thermally conductive layer 52 disposed on the lower surface of the heating element H. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the heating element H is temperature-controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0163] The line length of the phase-shift wiring 50-1 is set in accordance with the selection control of the heating elements H. The thermal conduction layer 52 and the phase change layer V are disposed across the multiple switching elements. The phase change layer V is thermally connected to the heating elements H via the thermal conduction layer 52. The phase change layer V generates heat in accordance with the selection status of the multiple heating elements H.

[0164] When a selector switch disposed at a junction with the main wiring is selected and transitions to the ON state, the phase-shift wiring 50-1 connected to the main wiring via the selector switch transitions to the ON state. When the heating element H connected to the phase-shift wiring 50-1 generates heat, the heat is conducted to the phase-change layer V via the thermal conduction layer 52 thermally connected to the heating element H. When the temperature of the phase-change layer V exceeds the insulating-to-metallic phase transition temperature, the phase-change layer V transitions to the metallic phase. The phase-change layer V that has transitioned to the metallic phase functions as a line for the phase-shift wiring.

[0165] FIG. 23 is a conceptual diagram illustrating an example of heat conduction in an extended structure of a phase shifter according to the present disclosure. Three switching elements are shown in FIG. 23. In the example of FIG. 23, the portion of the phase transition layer V in the insulating phase state and the portion of the phase transition layer V in the metallic phase state are indicated by different hatching. Switching elements E1 and E2 are in the ON state. The phase transition layer V in the portions of switching elements E1 and E2 is in the metallic phase state. Switching element E3 is in the OFF state. The phase transition layer V in the portion of switching element E3 is in the insulating phase state. When the phase shift wiring 50-1 has a junction with the main wiring on the left side (on the paper), the line length of the phase shift wiring 50-1 extends from the junction with the main wiring (not shown) to the switching element E2. Heat from the heating element H for heating the adjacent switching elements is conducted to the portion of the phase transition layer V located at the boundary between switching elements E1 and E2.

[0166] The phase of a signal propagated from a signal source (not shown) to a patch antenna (not shown) via the phase-shift wiring 50-1 is shifted in accordance with the line length of the phase-shift wiring 50-1 that has undergone a phase transition to the metallic phase. When the temperature of the phase-transition layer V falls below the insulating-to-metallic phase transition temperature, the phase-transition layer V undergoes a phase transition to the insulating phase, and the line length of the phase-shift wiring 50-1 becomes shorter. When the selection switch disposed at the junction with the main wiring transitions to a deselected OFF state, the phase-shift wiring 50-1 connected to the main wiring via the selection switch transitions to an OFF state.

[0167] [Configuration Example 5-2] 24 to 26 are conceptual diagrams showing an example of an extended structure (Configuration Example 5-2) of a phase shifter according to the present disclosure. Configuration Example 5-2 is an example in which heat conduction layers included in multiple switching elements are divided for each element. FIG. 24 is a plan view looking down on a portion of a phase shifter (phase shift wiring) from an upper viewpoint. FIG. 25 is a cross-sectional view taken along the KK section line in FIG. 24. FIG. 26 is a cross-sectional view taken along the LL section line in FIG. 24. The extended structure of the phase shifter of this configuration example differs from the extended structure of the phase shifter of Configuration Example 5-1 in that the phase transition layer and the heat conduction layer are covered with a heat conduction promotion layer. FIGS. 24 to 26 show a portion of the phase shift wiring whose line length can be extended depending on the selection of the heat-generating element.

[0168] The phase-shifting wiring 50-2 includes a substrate 51, a thermal conduction layer 52, a thermal conduction promotion layer 54, a phase transition layer V, and a plurality of heating elements H. A single switching element is formed by two heating elements H facing each other in a direction perpendicular to the extension direction of the phase-shifting wiring 50-2 and a portion of the phase transition layer V that undergoes a phase transition to a metallic phase in response to heat generation by the heating elements H. The two heating elements H facing each other in a direction perpendicular to the extension direction of the phase-shifting wiring 50-2 form a heating element pair. Signal lines and other wiring are omitted in FIGS. 24 to 26.

[0169] The substrate 51 has the same configuration as the substrate 11 of the first embodiment. The substrate 51 is an insulator (dielectric). The substrate 51 has a lower thermal conductivity than the phase transition layer V. The substrate 51 extends along the extension direction of the phase shift wiring 50-2.

[0170] The thermally conductive layer 52 has the same configuration as the thermally conductive layer 12 of the first embodiment. The thermally conductive layer 52 is disposed on the upper surface of the substrate 51. A phase transition layer V is disposed on the upper surface of the thermally conductive layer 52. A portion of the upper surface of the thermally conductive layer 52 is covered with a thermal conduction facilitation layer 54. The thermally conductive layer 52 is made of a material having a higher thermal conductivity than the substrate 51 and the phase transition layer V, but a lower thermal conductivity than the thermal conduction facilitation layer 54. The thermally conductive layer 52 extends on the upper surface of the substrate 51 along the extension direction of the phase-shifting wiring 50-2.

[0171] The phase change layer V has the same configuration as the phase change layer V of the first embodiment. The phase change layer V differs from the phase change layer V of the first embodiment in that the phase change layer V extends on the upper surface of the thermally conductive layer 52 along the extension direction of the phase-shifting wiring 50-2. The phase change layer V contains vanadium dioxide, which undergoes a phase transition from an insulating phase to a metallic phase at a phase transition temperature. The phase change layer V is disposed on the upper surface of the thermally conductive layer 52. The phase change layer V extends on the upper surface of the substrate 51 along the extension direction of the phase-shifting wiring 50-2. The phase change layer V is covered with a thermal conduction facilitating layer 54. Heat from the two heating elements H constituting the heating element pair is conducted to the phase change layer V via the thermally conductive layer 52 and the thermal conduction facilitating layer 54. The phase change layer V is configured to transition from an insulating phase to a metallic phase due to heat generated by the two heating elements H constituting the heating element pair.

[0172] At temperatures lower than the phase transition temperature, vanadium dioxide is in an insulating phase. Therefore, the switching element is in an off state at temperatures lower than the phase transition temperature. At temperatures higher than the phase transition temperature, vanadium dioxide is in a metallic phase. Therefore, the switching element is in an on state at temperatures higher than the phase transition temperature. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the phase transition layer V is adjusted to cross the phase transition temperature.

[0173] The heating element H has the same configuration as the heating element H in the first embodiment. The heating element H is disposed on the upper surface of the thermal conduction promotion layer 54. The heating element H and the phase transition layer V are disposed above the substrate 51. The heating element H is disposed at a distance from the phase transition layer V. The heating element H has an elongated rectangular shape extending perpendicular to the extension direction of the phase shift wiring 50-2. The heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled in response to selection via a TFT circuit (not shown). The heating element H is connected to a drive circuit (not shown) constituting the TFT circuit by a temperature control line. The TFT wiring includes multiple selection lines and multiple data lines. Two heating elements H constituting a heating element pair are connected to the same drive circuit. When the drive circuit connected to the two heating elements H in a pair is selected, the heating elements H generate heat. Heat from the heating element H is conducted to the phase transition layer V via the thermal conduction promotion layer 54 and the thermal conduction layer 52 disposed on the lower surface of the heating element H. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the heating element H is temperature-controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0174] The line length of the phase-shift wiring 50-2 is set in accordance with the selection control of the heat-generating elements H. The thermal conduction layer 52 and the phase change layer V are disposed across the multiple switching elements. The phase change layer V is thermally connected to the heat-generating elements H via the thermal conduction layer 52. The phase change layer V generates heat in accordance with the selection status of the multiple heat-generating elements H.

[0175] When a selector switch disposed at a junction with the main wiring is selected and transitions to the ON state, the phase-shift wiring 50-2 connected to the main wiring via the selector switch transitions to the ON state. When a heat-generating element H connected to the phase-shift wiring 50-2 generates heat, the heat is conducted to the phase-change layer V via the heat conduction promotion layer 54 and the thermal conduction layer 52, which are thermally connected to the heat-generating element H. When the temperature of the phase-change layer V exceeds the insulating-to-metallic phase transition temperature, the phase-change layer V transitions to the metallic phase. The phase-change layer V, which has transitioned to the metallic phase, functions as a line for the phase-shift wiring.

[0176] FIG. 27 is a conceptual diagram illustrating an example of heat conduction in an extended structure of a phase shifter according to the present disclosure. Three switching elements are shown in FIG. 27. In the example of FIG. 27, the portions of the phase transition layer V in the insulating phase state and the portions of the phase transition layer V in the metallic phase state are indicated by different hatching. The switching elements E1 and E2 are in the ON state. The phase transition layers V in the portions of the switching elements E1 and E2 are in the metallic phase state. The switching element E3 is in the OFF state. The phase transition layer V in the portion of the switching element E3 is in the insulating phase state. When the phase shift wiring 50-2 has a junction with the main wiring on the left side (on the paper), the line length of the phase shift wiring 50-2 extends from the junction with the main wiring (not shown) to the switching element E2. In this configuration example, the heat conduction promotion layers 54 constituting adjacent switching elements are divided. In addition, in this configuration example, the thermal conduction promotion layer 54 has a higher thermal conductivity than the thermal conduction layer 52, so the heat from the heating element H is more likely to be conducted to the thermal conduction promotion layer 54. Therefore, according to this configuration example, the heat from the heating element H, which is used to heat the adjacent switching elements, is less likely to be conducted to the portion of the phase transition layer V located at the boundary between the switching element E1 and the switching element E2.

[0177] The phase of a signal propagated from a signal source (not shown) to a patch antenna (not shown) via the phase-shift wiring 50-2 is shifted in accordance with the line length of the phase-shift wiring 50-2 that has undergone a phase transition to the metallic phase. When the temperature of the phase-transition layer V falls below the insulating-to-metallic phase transition temperature, the phase-transition layer V undergoes a phase transition to the insulating phase, shortening the line length of the phase-shift wiring 50-2. When the selection switch disposed at the junction with the main wiring transitions to a deselected OFF state, the phase-shift wiring 50-2 connected to the main wiring via the selection switch transitions to an OFF state.

[0178] As described above, the phase shifter of this embodiment can realize an extended structure in which the switching elements of the first to fourth embodiments are extended along one axis. By using the extended structure of this embodiment, a phase shifter with variable line length can be realized.

[0179] (Sixth embodiment) Next, an antenna device according to a sixth embodiment will be described with reference to the drawings. The antenna device of the present disclosure includes a planar antenna including the phase shifter of the fifth embodiment. The following configuration is an example and does not limit the configuration of the antenna device of the present disclosure.

[0180] (composition) FIG. 28 is a conceptual diagram showing an example of the configuration of an antenna device according to the present disclosure. FIG. 28 shows an example of the external appearance of an antenna device according to the present disclosure. The antenna device 600 includes a planar antenna 6. The planar antenna 6 includes a phase shifter according to the fifth embodiment. An antenna array 60 is arranged on the upper surface of the planar antenna 6, and is composed of a plurality of patch antennas P arranged in a two-dimensional array. The plurality of patch antennas P are arranged along the X and Y directions. The plurality of patch antennas P are arranged in a phased array. Each of the plurality of patch antennas P constitutes an antenna element. Each antenna element is independently controlled. The planar antenna 6 includes a TFT circuit (not shown) composed of TFTs (Thin Film Transistors). The TFT circuit is used to select a patch antenna P to be used for transmitting and receiving radio waves.

[0181] The antenna device 600 is equipped with a first drive circuit 671 and a second drive circuit 672. The first drive circuit 671 and the second drive circuit 672 are circuits used to select the patch antenna P to be driven. By driving the first drive circuit 671 and the second drive circuit 672, it is possible to specify an address associated with each of the multiple patch antennas P. For example, the first drive circuit 671 and the second drive circuit 672 are formed on the surface of the planar antenna 6. The first drive circuit 671 and the second drive circuit 672 may also be formed inside the planar antenna 6.

[0182] Fig. 29 is a conceptual diagram showing a cross section of a portion of a planar antenna included in an antenna device according to the present disclosure. Fig. 29 shows a cross section of the planar antenna cut along the MM cutting line shown in Fig. 28. Fig. 29 shows one of the multiple antenna elements that make up the planar antenna. The planar antenna 6 includes an antenna substrate 610, a temperature control substrate 630, a phase transition layer V, a thermal conduction layer 620, a heat generating element H, a drive circuit D, and a patch antenna P.

[0183] The antenna substrate 610 includes a first substrate 611 and a second substrate 612. The first substrate 611 and the second substrate 612 are insulators (dielectrics). The first substrate 611 and the second substrate 612 are made of a material with low dielectric loss. The first substrate 611 and the second substrate 612 are preferably made of a material with high insulation and low dielectric loss, such as a ceramic material or glass. The first substrate 611 and the second substrate 612 may be made of a polymer or synthetic material. The lower the dielectric loss of the first substrate 611 and the second substrate 612, the more effectively electromagnetic waves such as high frequency waves and microwaves can be controlled. For example, at least one of the first substrate 611 and the second substrate 612 may be made of a multilayer substrate with low transmission loss. For example, at least one of the first substrate 611 and the second substrate 612 may be made of an alumina substrate.

[0184] A patch antenna P is disposed on the upper surface of the first substrate 611. A ground layer G is disposed between the lower surface of the first substrate 611 and the upper surface of the second substrate 612. An opening W is formed in the ground layer G. The opening W is formed below the patch antenna P. A phase transition layer V is disposed on the lower surface of the second substrate 612.

[0185] The phase change layer V has the same configuration as the phase change layer V in the first embodiment. The phase change layer V is disposed on the lower surface of the second substrate 612. A thermally conductive layer 620 is disposed on the lower surface of the phase change layer V. The phase change layer V is thermally connected to the heating element H via the thermally conductive layer 620. The structure for thermally connecting the phase change layer V to the heating element H may be the same as the structure of any of the switching elements in the first to fourth embodiments. For example, the thermally conductive layer 620 may be disposed on the lower surface of the second substrate 612, and the phase change layer V may be disposed on the lower surface of the thermally conductive layer 620. Heat generated from the heating element H is conducted to the phase change layer V via the thermally conductive layer 620. The phase change layer V is configured to undergo a phase transition from an insulating phase to a metallic phase due to heat generation by the heating element H. The phase change layer V is electrically connected to the first signal line S1 and the second signal line S2. The phase change layer V is disposed between the first signal line S1 and the second signal line S2 and functions as a switch.

[0186] Additionally, a first signal line S1 and a second signal line S2 connected to the phase change layer V are arranged on the lower surface of the second substrate 612. The first signal line S1 is connected to a signal source (not shown) via a phase shift wiring (not shown). The first signal line S1 is a line through which a signal phase-shifted by the phase shift wiring propagates. The second signal line S2 extends to below the patch antenna P. The second signal line S2 is a line through which the phase-shifted signal propagates to the patch antenna P. An opening W is interposed between the second signal line S2 and the patch antenna P. The layer on which the phase change layer V, the first signal line S1, and the second signal line S2 are arranged forms a phase shift layer.

[0187] The patch antenna P is a plate-shaped radiating element. For example, the patch antenna P is rectangular. The shape of the patch antenna P is not limited to rectangular, but may be circular or another shape. The patch antenna P is fed by an electromagnetic coupling feeding method. The patch antenna P is electromagnetically coupled to the second signal line S2 formed on the underside of the second substrate 612 through an opening W. The patch antenna P is excited by electromagnetic coupling between the patch antenna P and the second signal line S2 through the opening W. The patch antenna P has a structure equivalent to a microstrip line with both ends open. The resonant frequency of the patch antenna P is an integer multiple of the wavelength corresponding to the length of one side of the patch antenna P. The size of the patch antenna P is set according to the wavelength of the radio waves to be transmitted. The patch antenna P may be configured to be wired to the second signal line S2 via a conductor. The patch antenna P may also be configured to be formed on the same surface as the second signal line S2 and directly connected to the second signal line S2. In this case, the phase-shift wiring arranged on the phase-shift layer and the second signal line S2 are configured to be electromagnetically coupled.

[0188] The ground layer G is disposed between the first substrate 611 and the second substrate 612. The ground layer G may be formed on the lower surface of the first substrate 611 or on the upper surface of the second substrate 612. The ground layer G blocks electromagnetic coupling above and below the ground layer G. The ground layer G is made of a conductor. For example, the material of the ground layer G is a metal (including an alloy) such as copper, aluminum, or chromium. The potential of the ground layer G is the ground potential. Therefore, a capacitance according to the dielectric constant of the second substrate 612 is formed between the ground layer G and the phase shift layer including the phase transition layer V, the first signal line S1, the second signal line S2, and the phase shift wiring (not shown).

[0189] The temperature control substrate 630 is a substrate on which a TFT circuit is formed. For example, the material of the temperature control substrate 630 is an insulator (dielectric). The temperature control substrate 630 is made of a material with low dielectric loss. For example, the temperature control substrate 630 is made of a material with high insulation and low dielectric loss, such as a ceramic material or glass. The temperature control substrate 630 may be made of a polymer or synthetic material. The lower the dielectric loss of the temperature control substrate 630, the more effectively it can control electromagnetic waves such as high frequency waves and microwaves. For example, the temperature control substrate 630 is made of a multilayer substrate with low transmission loss. For example, the temperature control substrate 630 may be made of an alumina substrate.

[0190] A driving circuit D and a heating element H are arranged on the upper surface of the temperature control board 630. The driving circuit D and the heating element H are connected to each other via a temperature control line L H The driving circuit D is one element that constitutes the TFT circuit. The layer on which the heating elements H are arranged has TFT wiring (not shown) formed thereon for controlling the temperature of the heating elements H. The TFT wiring includes a plurality of selection lines used to select the driving circuit D and a plurality of data lines used to write phase shift data to the phase shifter.

[0191] The heating element H has the same configuration as in the first embodiment. The heating element H is disposed on the upper surface of the temperature control substrate 630. The heating element H is disposed so that its upper surface is in contact with the thermal conduction layer 620. The heating element H has an elongated rectangular shape along a direction perpendicular to the extending direction of the first signal line S1 and the second signal line S2. The heating element H is smaller than the phase transition layer V. The temperature of the heating element H is controlled according to selection via a TFT circuit (not shown). The heating element H is connected to the temperature control line L HThe heating element H is connected to a drive circuit D that constitutes a TFT circuit by a TFT wiring. The TFT wiring includes multiple selection lines and multiple data lines. When a drive circuit D connected to a heating element H is selected, the heating element H generates heat. The heat from the heating element H is conducted to the phase transition layer V disposed above the heating element H via the thermal conduction layer 620. The resistance change during the phase transition between the insulating phase and the metallic phase of vanadium dioxide exhibits hysteresis characteristics. Therefore, taking the hysteresis characteristics into consideration, the temperature of the heating element H is controlled so that the temperature of the phase transition layer V crosses the phase transition temperature.

[0192] 30 is a block diagram showing an example of the configuration of an antenna device according to the present disclosure. The antenna device 600 includes an antenna array 60, a phase shifter 61, a matrix circuit 62, a driver circuit 67, a control circuit 68, and a signal source 69.

[0193] The phase shifter 61 is configured for each patch antenna. The phase shifter 61 includes a phase shift wiring (not shown), a first signal line S1, a second signal line S2, a phase transition layer V, a heating element H, and a temperature control line L. H The amount of phase shift of the phase shifter 61 is set according to the line length of the line formed by the phase shift wiring, the first signal line S1, the second signal line S2, and the phase transition layer V, and the dielectric constants of the antenna substrate 610 and the temperature control substrate 630.

[0194] The matrix circuit 62 has a configuration in which a plurality of thin film transistors (TFTs) are arranged in a two-dimensional array. The matrix circuit 62 is formed using TFT process technology. For example, a shield layer is formed above the matrix circuit 62. The shield layer is formed to prevent electromagnetic coupling between the top and bottom of the shield layer. For example, the shield layer includes a conductor. The potential of the shield layer is basically the ground potential. Therefore, a capacitance is formed between the signal line included in the phase shifter 61 and the shield layer according to the dielectric constant of a dielectric layer such as an insulating layer or a TFT substrate. Each of the plurality of TFTs included in the matrix circuit 62 corresponds to one of the plurality of patch antennas P included in the antenna array 60. For example, the TFT includes a semiconductor layer such as amorphous silicon or polysilicon.

[0195] The drive circuit 67 includes a first drive circuit 671 and a second drive circuit 672. The first drive circuit 671 is a circuit for specifying addresses in the X direction. The first drive circuit 671 is connected to a plurality of lines extending in the Y direction. The second drive circuit 672 is a circuit for specifying addresses in the Y direction. The second drive circuit 672 is connected to a plurality of lines extending in the X direction. The drive circuit 67 can specify addresses associated with each patch antenna P by controlling the first drive circuit 671 and the second drive circuit 672. The drive circuit 67 drives a plurality of TFTs included in the matrix circuit 62 under the control of the control circuit 68. The drive circuit 67 individually drives a plurality of TFTs arranged in a two-dimensional array.

[0196] The control circuit 68 drives the drive circuit 67 in response to an external control signal. The control circuit 68 drives the drive circuit 67 using an active matrix drive system. The control circuit 68 also outputs the external control signal to a signal source 69. For example, the control circuit 68 is realized by a microcomputer (also called a microcomputer) or a microcontroller. For example, the control circuit 68 includes a processor and memory. For example, the control circuit 68 includes a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), flash memory, etc. The control circuit 68 controls the operation of the antenna device 600 by causing the processor to execute a program stored in advance in memory, etc. The control circuit 68 executes control according to the program in accordance with a preset schedule, timing, external control instructions, etc. For example, the control circuit 68 controls the antenna array 60, which is composed of multiple patch antennas P included in the planar antenna 6, to transmit directional radio waves from the antenna array 60. In this way, the antenna array 60 is used as a phased array antenna.

[0197] The signal source 69 is connected to a switch group formed by a plurality of switching elements included in a plurality of antenna elements included in the phase shifter 61. The signal source 69 is also connected to the control circuit 68. The signal source 69 receives a control signal from the control circuit 68. The signal source 69 controls the on / off of the plurality of switching elements that make up the switch group in response to the control signal. The signal source 69 may be configured to receive the control signal directly from the outside without going through the control circuit 68.

[0198] A signal that reaches the signal input section of the phase shifter 61 through a signal line (not shown) connected to an on-state TFT is phase-shifted by an amount corresponding to the line length set in the phase shifter 61 and the dielectric constant of the dielectric material including the antenna substrate 610 and the temperature control substrate 630. The phase-shifted signal propagates from the second signal line S2 to the patch antenna P by electromagnetic coupling. The signal propagated to the patch antenna P is transmitted from the patch antenna P as a radio wave to be transmitted. The radio wave transmitted from the patch antenna P is derived from a signal output from a transmission circuit (not shown). There are no particular limitations on the information contained in the signal.

[0199] Furthermore, the radio waves received by the patch antenna P are received according to a capacitance based on the dielectric constant of the antenna substrate 610 interposed between the patch antenna P and the second signal line S2. The phase of the received radio waves is shifted by an amount corresponding to the line length set in the phase shifter 61 and the dielectric constants of the antenna substrate 610 and the temperature control substrate 630. The phase-shifted signal is received by a receiving circuit (not shown) through the signal line. Information contained in the signal received by the receiving circuit is decoded by a decoder (not shown).

[0200] As described above, the antenna device of this embodiment includes a planar antenna including multiple patch antennas. The planar antenna includes an antenna substrate and a temperature control substrate. The antenna substrate includes an antenna array composed of multiple patch antennas arranged in an array, and switching elements associated with each of the multiple patch antennas. The temperature control substrate includes a drive circuit for driving each switching element associated with each of the multiple patch antennas. The switching element includes a phase change layer, a thermally conductive layer, and a heating element. The phase change layer is made of a material that undergoes a metal-insulator phase transition. The phase change layer is arranged on a signal line through which a signal to be transmitted or received propagates. The thermally conductive layer is an insulator with a higher thermal conductivity than the phase change layer. The thermally conductive layer is formed on the surface of the phase change layer. The heating element is rectangular, with long sides perpendicular to the extension direction of the signal line and short sides shorter than the sides of the phase change layer. The heating element is thermally connected to the phase change layer and the thermally conductive layer.

[0201] The antenna device of this embodiment includes at least one of the switching elements of the first to fourth embodiments. The switching element included in the antenna device of this embodiment can efficiently cause a phase transition of the phase transition layer even if the size of the heating element is reduced. Therefore, this embodiment can reduce power consumption. Furthermore, the configuration of this embodiment allows the signal line and the heating element to be positioned apart, making high-frequency coupling between the signal line and the heating element less likely to occur. Therefore, this embodiment can realize an antenna device with high dielectric properties.

[0202] By controlling the multiple patch antennas included in the planar antenna provided in the antenna device of this embodiment, it is possible to transmit directional radio waves from an antenna array formed by the multiple patch antennas. In other words, the antenna array formed by the multiple patch antennas can be used as a phased array antenna.

[0203] Seventh embodiment Next, a switching element according to a seventh embodiment will be described with reference to the drawings. The switching element according to this embodiment has a simplified configuration of the switching elements according to the first to fourth embodiments.

[0204] 31 is a conceptual diagram showing an example of the configuration of a switching element according to the present disclosure. The switching element 70 includes a phase transition layer V, a thermal conduction layer 72, and a heat generating element H.

[0205] The phase transition layer V is made of a material that undergoes a metal-insulator phase transition. The phase transition layer V is disposed on the signal line S through which the signal to be transmitted or received propagates. The thermal conduction layer 72 is an insulator with a higher thermal conductivity than the phase transition layer. The thermal conduction layer 72 is formed on the surface of the phase transition layer. The heating element H is rectangular, with long sides perpendicular to the extension direction of the signal line and short sides shorter than the sides of the phase transition layer. The heating element H is thermally connected to the phase transition layer and the thermal conduction layer.

[0206] The switching element of this embodiment includes a phase transition layer made of a material that undergoes a metal-insulator phase transition. A thermally conductive layer having a higher thermal conductivity than the phase transition layer is formed on the surface of the phase transition layer. The phase transition layer and the thermally conductive layer are thermally connected to a heating element. When the heating element generates heat, the phase transition layer is uniformly heated via the thermally conductive layer formed on the surface. Therefore, with the configuration of this embodiment, the phase transition layer made of a material that undergoes a metal-insulator phase transition can be efficiently phase-transitioned even if the size of the heating element is reduced.

[0207] For example, the functions of the components included in the switching element in this embodiment are realized by the functions of the components included in the switching elements in the first to fourth embodiments. For example, the switching element in this embodiment is applied to the extension structure of the phase shifter in the fifth embodiment. For example, the switching element in this embodiment is controlled by a control system included in the antenna device in the sixth embodiment.

[0208] (Hardware) Next, a hardware configuration for executing the control in the present disclosure will be described with reference to the drawings. Fig. 32 is a block diagram showing an example of a hardware configuration for executing the control in the present disclosure. Here, an information processing device 90 (computer) is shown as an example of the hardware configuration. The information processing device in Fig. 32 is an example of a configuration for executing the control in the present disclosure and does not limit the scope of the present disclosure.

[0209] As shown in Fig. 32, an information processing device 90 includes a processor 91, a memory 92, an auxiliary storage device 93, an input / output interface 95, and a communication interface 96. In Fig. 32, interface is abbreviated as I / F (Interface). The information processing device 90 may include a plurality of at least any of the processor 91, memory 92, auxiliary storage device 93, input / output interface 95, and communication interface 96. The processor 91, memory 92, auxiliary storage device 93, input / output interface 95, and communication interface 96 are connected to each other via a bus 98 so as to be able to communicate data with each other. Furthermore, the processor 91, memory 92, auxiliary storage device 93, and input / output interface 95 are connected to a network such as the Internet or an intranet via the communication interface 96.

[0210] The processor 91 loads a program (instructions) stored in an auxiliary storage device 93 or the like into the memory 92. For example, the program is a software program for executing the control in the present disclosure. The processor 91 executes the program loaded into the memory 92. The processor 91 executes the control in the present disclosure by executing the program. The processor 91 may be configured by a single piece of hardware or may be configured by multiple pieces of hardware.

[0211] The memory 92 is a storage device having an area in which a program is loaded. The processor 91 loads a program stored in an auxiliary storage device 93 or the like into the memory 92. The memory 92 is realized by a volatile memory such as a DRAM (Dynamic Random Access Memory). Alternatively, a non-volatile memory such as an MRAM (Magnetoresistive Random Access Memory) may be used as the memory 92. The memory 92 may be configured by a single piece of hardware or by multiple pieces of hardware.

[0212] The auxiliary storage device 93 stores various data such as programs. For example, the auxiliary storage device 93 is realized by a local disk such as a hard disk or flash memory. The auxiliary storage device 93 may be configured by a single piece of hardware or by multiple pieces of hardware. The auxiliary storage device 93 may also be configured as external hardware. It is also possible to configure the system so that various data is stored in the memory 92, and omit the auxiliary storage device 93.

[0213] The input / output interface 95 is an interface for connecting the information processing device 90 to peripheral devices based on standards and specifications. The communication interface 96 is an interface for connecting to external systems and devices via a network such as the Internet or an intranet based on standards and specifications. The input / output interface 95 may be configured by a single piece of hardware, or may be configured by multiple pieces of hardware. The input / output interface 95 and the communication interface 96 may be a common interface for connecting to external devices.

[0214] Input devices such as a keyboard, mouse, and touch panel may be connected to the information processing device 90 as needed. These input devices are used to input information and settings. When a touch panel is used as the input device, a screen having the function of the touch panel serves as the interface. The processor 91 and the input devices are connected via an input / output interface 95.

[0215] The information processing device 90 may be equipped with a display device for displaying information. When a display device is equipped, the information processing device 90 is equipped with a display control device (not shown) for controlling the display of the display device. The information processing device 90 and the display device are connected via an input / output interface 95.

[0216] The information processing device 90 may be equipped with a drive device. The drive device acts as an intermediary between the processor 91 and a recording medium (program recording medium) to read data and programs stored on the recording medium and to write processing results of the information processing device 90 to the recording medium. The information processing device 90 and the drive device are connected via an input / output interface 95.

[0217] The above is an example of a hardware configuration for enabling the control in the present disclosure. The hardware configuration in Fig. 32 is an example of a hardware configuration for executing the control in the present disclosure and does not limit the scope of the present disclosure. A program that causes a computer to execute the control in the present disclosure is also included in the scope of the present disclosure.

[0218] A program recording medium on which a program for executing the processing in this embodiment is recorded is also included in the scope of the present invention. For example, the program recording medium is a computer-readable non-transitory recording medium. The recording medium can be realized as an optical recording medium such as a CD (Compact Disc) or a DVD (Digital Versatile Disc). The recording medium may also be realized as a semiconductor recording medium such as a USB (Universal Serial Bus) memory or an SD (Secure Digital) card. The recording medium may also be realized as a magnetic recording medium such as a flexible disk or other recording medium.

[0219] The components in the present disclosure may be combined in any manner. The components in the present disclosure may be realized by software. The components in the present disclosure may be realized by circuits.

[0220] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0221] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. (Appendix 1) a phase transition layer made of a material that undergoes a metal-insulator phase transition and disposed on a signal line through which a signal to be transmitted or received propagates; a thermally conductive layer formed on the surface of the phase change layer, the thermally conductive layer being an insulator having a higher thermal conductivity than the phase change layer; a heating element that is rectangular in shape and has long sides perpendicular to the extension direction of the signal line and short sides that are shorter than the side lengths of the phase transition layer, and that is thermally connected to the phase transition layer and the thermal conduction layer. (Appendix 2) The phase transition layer is 2. The switching element according to claim 1, containing vanadium dioxide as a substance that undergoes a metal-insulator phase transition. (Appendix 3) 3. The switching element according to claim 2, wherein the phase transition layer is disposed between the heat generating element and the thermally conductive layer. (Appendix 4) 3. The switching element according to claim 2, wherein the thermally conductive layer is disposed between the phase transition layer and the heat generating element. (Appendix 5) 5. The switching element according to claim 3, further comprising a thermal conduction promotion layer that is an insulator having a higher thermal conductivity than the thermal conduction layer and is thermally connected to the phase transition layer. (Appendix 6) 5. The switching element according to claim 3, wherein the phase transition layer is connected to the signal line via metal vanadium. (Appendix 7) 3. The switching element according to claim 2, wherein the phase transition layer and the heating element are arranged on the same surface of the thermally conductive layer with a gap between them. (Appendix 8) 8. The switching element according to claim 7, wherein at least one of the phase transition layer, the heat generating element, and the thermal conduction layer is covered with a thermal conduction promotion layer that is an insulator having a higher thermal conductivity than the thermal conduction layer. (Appendix 9) a heat conduction promotion layer that is an insulator having a higher thermal conductivity than the heat conduction layer and is thermally connected to the phase transition layer; 3. The switching element according to claim 2, wherein the phase transition layer and the heat generating element are arranged on the same side of the thermal conduction promotion layer with an interval therebetween. (Appendix 10) an antenna substrate on which an antenna array constituted by a plurality of patch antennas arranged in an array and switching elements corresponding to each of the plurality of patch antennas are arranged; a temperature control substrate on which a thin film transistor circuit is arranged that controls the temperature of the switching element associated with each of the plurality of patch antennas, The switching element is a phase transition layer made of a material that undergoes a metal-insulator phase transition and disposed on a signal line through which a signal to be transmitted or received propagates; a thermally conductive layer formed on the surface of the phase change layer, the thermally conductive layer being an insulator having a higher thermal conductivity than the phase change layer; A planar antenna having a rectangular shape with long sides perpendicular to the extension direction of the signal line and short sides shorter than the side length of the phase transition layer, and a heat-generating element thermally connected to the phase transition layer and the thermal conduction layer. [Explanation of symbols]

[0222] 6 Planar Antenna 10, 20, 30, 40, 70 Switching element 11, 21, 31, 41 boards 12, 22, 32, 42, 72 Heat conduction layer 13, 23, 43, 44 Heat conduction promotion layer 16, 26, 37 Insulation layer 27 Insulating layer 50 phase shift wiring 51 PCB 52 Thermal Conduction Layer 54 Heat conduction promotion layer 60 Antenna Array 61 Phase shifter 62 Matrix Circuit 67 Drive Circuit 68 Control Circuit 69 Signal source 600 Antenna Equipment 610 Antenna board 611 First board 612 Second board 620 Thermal Conduction Layer 630 Temperature Control Board 671 First drive circuit 672 Second drive circuit

Claims

1. a phase transition layer made of a material that undergoes a metal-insulator phase transition and disposed on a signal line through which a signal to be transmitted or received propagates; a thermally conductive layer formed on the surface of the phase change layer, the thermally conductive layer being an insulator having a higher thermal conductivity than the phase change layer; a heating element that is rectangular in shape and has long sides perpendicular to the extension direction of the signal line and short sides that are shorter than the side lengths of the phase transition layer, and that is thermally connected to the phase transition layer and the thermal conduction layer.

2. The phase transition layer is 2. The switching element according to claim 1, wherein the substance that undergoes metal-insulator phase transition contains vanadium dioxide.

3. The switching element according to claim 2 , wherein the phase change layer is disposed between the heating element and the thermally conductive layer.

4. The switching element according to claim 2 , wherein the thermally conductive layer is disposed between the phase transition layer and the heat generating element.

5. 5. The switching element according to claim 3, further comprising a heat conduction promotion layer, the heat conduction promotion layer being an insulator having a higher thermal conductivity than the heat conduction layer and thermally connected to the phase transition layer.

6. 5. The switching element according to claim 3, wherein the phase transition layer is connected to the signal line via metal vanadium.

7. 3. The switching element according to claim 2, wherein the phase change layer and the heating element are disposed on the same surface of the thermally conductive layer with a space therebetween.

8. 8. The switching element according to claim 7, wherein at least one of the phase transition layer, the heat generating element, and the thermal conduction layer is covered with a thermal conduction promotion layer that is an insulator having a higher thermal conductivity than the thermal conduction layer.

9. a heat conduction promotion layer that is an insulator having a higher thermal conductivity than the heat conduction layer and is thermally connected to the phase transition layer; 3. The switching element according to claim 2, wherein the phase transition layer and the heat generating element are arranged on the same side of the thermal conduction promotion layer with a gap therebetween.

10. an antenna substrate on which an antenna array constituted by a plurality of patch antennas arranged in an array and switching elements corresponding to each of the plurality of patch antennas are arranged; a temperature control board, in which a drive circuit for driving the switching element corresponding to each of the plurality of patch antennas is arranged for each of the switching elements; The switching element is a phase transition layer made of a material that undergoes a metal-insulator phase transition and disposed on a signal line through which a signal to be transmitted or received propagates; a thermally conductive layer formed on the surface of the phase change layer, the thermally conductive layer being an insulator having a higher thermal conductivity than the phase change layer; A planar antenna having a rectangular shape with long sides perpendicular to the extension direction of the signal line and short sides shorter than the side length of the phase transition layer, and a heat-generating element thermally connected to the phase transition layer and the thermal conduction layer.

Images