THERMAL RADIATION ELEMENT, THERMAL RADIATION ELEMENT MODULE, AND THERMAL RADIATION LIGHT SOURCE

A thermal radiation element includes a substrate; and a plasmonic perfect absorber in which a first conductor layer covering one main surface of the substrate, an insulator layer, and a second conductor layer are laminated in this order, in which the first conductor layer is provided with electrodes through which a current flows in an in-plane direction of a main surface of the first conductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2021-106816, filed on Jun. 28, 2021, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a thermal radiation element. The present invention also relates to a thermal radiation element module and a thermal radiation light source, each of which includes the thermal radiation element.

Related Art

In recent years, ideas for obtaining optical property independent of a material by forming a microstructure on a material surface have been widely studied. Examples of the microstructure include a plasmonic structure, and a plasmonic perfect absorber has been reported as one of plasmonic structures. The plasmonic perfect absorber has a high absorptance in a specific wavelength band, among plasmonic structures. The plasmonic perfect absorber is a resonator structure in which a conductor, an insulator, and a conductor are stacked, and also referred to as a metal-insulator-metal (MIM) structure.

According to Kirchhoff's law, the emissivity is equal to the absorptance in opaque. It has also been reported that the emissivity at a material surface can be controlled using the MIM structure. The emissivity is represented by a ratio between radiation intensities of a real surface and a blackbody surface. Planck's law defines thermal radiation at the blackbody surface, and a value obtained by multiplying the thermal radiation by the emissivity is thermal radiation at the real surface. Thermal radiation is a phenomenon in which thermal energy of an object, such as a blackbody or MIM structure, is emitted as electromagnetic waves according to a temperature of the object. The term “radiation” hereinafter refers to thermal radiation unless otherwise specified.

JP 2018-136576 A can be cited as a prior art document related to emissivity control. JP 2018-136576 A discloses a technique of performing thermal radiation of narrow-band infrared rays by wavelength control of emissivity using the MIM structure.

As described in JP 2020-64820 A, a thermal radiation light source to which the emissivity control using the MIM structure is applied is already known. JP 2020-64820 A discloses a technique of suppressing oxidation of the MIM structure that may occur when the MIM structure is operated in the atmosphere by using a layer suppressing oxidation as a surface layer.

Meanwhile, as illustrated in FIG. 1B of JP 2018-136576 A and FIG. 1 of JP 2020-64820 A, the MIM structure is laminated on a substrate (which is a base in JP 2018-136576 A). Hereinafter, the substrate and the MIM structure laminated on the substrate are collectively referred to as a thermal radiation element.

For utilizing the thermal radiation using such a thermal radiation element, it is essential to heat the MIM structure to a predetermined operating temperature. The higher the operating temperature is, the higher the intensity of the thermal radiation is, while the radiation on a shorter wavelength is emitted. The temperature is a balance of thermal energy. The temperature increases as an input amount increases with respect to a loss amount of thermal energy. When the same materials have the same energy, an amount of rise in temperature depending on a volume. Thermal energy required to raise the temperature of an object by 1° C. is defined as in the following Equation (1), wherein heat capacity is denoted by C [J/° C.], specific heat is denoted by c [J/kg·° C.], density is denoted by ρ [kg/m3], and volume is denoted by V [m3]:

JP 2020-64820 A stated above describes, as a method of heating the MIM structure in the thermal radiation light source, a method of self-heating a substrate by energizing the substrate and a method of externally heating the substrate and the MIM structure using an external heating unit (for example, a heater). In any of these methods, a heat transfer path passes through the substrate when heating the MIM structure. As described above, when viewed from the MIM structure, the substrate functions as a heat source. Therefore, in order to cause the temperature of the MIM structure to reach the operating temperature described above, it is necessary to keep the temperature of the substrate, which is a heat source, equal to or higher than the operating temperature.

Since the substrate is thicker than the MIM structure, the volume inevitably increases. In other words, the heat capacity C of the substrate must be larger than the heat capacity C of the MIM structure. Therefore, the conventional method of heating the entire MIM structure using the substrate as a heat source (for example, the method described in JP 2020-64820 A) can be further improved in terms of energy efficiency.

One aspect of the present invention has been made to solve the problems stated above, which is intended to enhance energy efficiency as compared with in the thermal radiation element of JP 2020-64820 A which is the conventional invention. Another aspect of the present invention is intended to provide a thermal radiation element module and a thermal radiation light source, each of which includes the thermal radiation element having higher energy efficiency than conventional elements.

SUMMARY OF THE INVENTION

In order to implement the aspect of the present invention, a thermal radiation element according to one aspect of the present invention includes: a substrate made of an insulator having a pair of main surfaces; and a plasmonic perfect absorber in which a first conductor layer covering at least a part of one main surface of the substrate, an insulator layer, and a second conductor layer are laminated in this order. The thermal radiation element adopts a configuration in which the first conductor layer is provided with electrodes through which a current flows in an in-plane direction of a main surface of the first conductor layer.

In order to implement the aspect of the present invention, a thermal radiation element module according to one aspect of the present invention includes the thermal radiation element according to one aspect of the present invention; and a housing provided with a cavity that houses the thermal radiation element and a power terminal that supplies power to the electrode. In the thermal radiation element module, at least a part of the substrate is fixed to the cavity using a bonding member inside the cavity.

In order to implement the aspect of the present invention, a thermal radiation light source according to one aspect of the present invention includes the thermal radiation element module according to one aspect of the present invention.

According to one aspect of the present invention, it is possible to enhance energy efficiency as compared with the thermal radiation element of JP 2020-64820 A which is the conventional invention. According to another aspect of the present invention, it is possible to provide a thermal radiation element module and a thermal radiation light source, each of which includes the thermal radiation element having higher energy efficiency than conventional elements.

DESCRIPTION OF THE EMBODIMENTS

A thermal radiation element module M according to one embodiment of the present invention will be described with reference toFIGS.1to3.FIG.1includes an upper view that is a plan view of the thermal radiation element module M, and a lower view that is a cross-sectional view of the thermal radiation element module M. The plan view of the thermal radiation element module M is obtained when an opening APCof a cavity C provided in a housing20is viewed in plan view from a normal direction of a main surface of an optical window23. The cross-sectional view of the thermal radiation element module M is obtained in a cross section along the normal direction of a main surface of the optical window23and including a thermal radiation element1.FIG.2is a cross-sectional view of the thermal radiation element1, and is an enlarged view of a part of the thermal radiation element1shown inFIG.1. InFIG.2, each component is enlarged in a thickness direction.FIG.3is an enlarged perspective view in which a part of a plasmonic perfect absorber10included in the thermal radiation element1is enlarged.

[Configuration of Thermal Radiation Element Module]

As illustrated in the upper and lower views ofFIG.1, the thermal radiation element module M includes a plasmonic perfect absorber10, a substrate14, a housing20, an optical window23, a bonding member24, a bonding member31, a metal wire32, and power terminals41and42.

In a configuration of the thermal radiation element module M, the substrate14and the plasmonic perfect absorber10constitute the thermal radiation element1according to the aspect of the present invention.

Additionally, the thermal radiation element module M emits electromagnetic waves (in particular, at least one of visible light, near-infrared light, mid-infrared light, and far-infrared light) caused by thermal radiation by energizing a conductor layer13constituting a part of the plasmonic perfect absorber10using the power terminals41and42. As described above, the thermal radiation element module M functions as a thermal radiation light source that emits electromagnetic waves of at least one of visible light, near-infrared light, mid-infrared light, and far-infrared light. That is, the thermal radiation light source using the thermal radiation element module M is also included in the scope of the present invention. The thermal radiation light source may include the thermal radiation element module M and a power supply module that supplies power to the thermal radiation element module M via the power terminals41and42.

The thermal radiation element module M is configured to cause a current to flow in an in-plane direction of the conductor layer13using the power terminals41and42. The current flowing in the in-plane direction of the conductor layer13generates Joule heat. Therefore, the electromagnetic waves stated above are emitted by heating the thermal radiation element1to a predetermined operating temperature using thermal energy in the thermal radiation element module M. The operating temperature of the thermal radiation element1can be appropriately determined to be within a temperature range in which eutectic reaction does not occur in the plasmonic perfect absorber10. The higher the operating temperature is, the higher intensity the light emitted by the plasmonic perfect absorber10has. In the thermal radiation element1described in the present embodiment, the operating temperature is assumed to be 300° C. or more and 1200° C. or less.

The substrate14is a plate-like member made of an insulator having a pair of main surfaces14aand14b. In a state illustrated inFIG.2, the main surface14ais located on an upper side, and the main surface14bis located on a lower side. A shape of the substrate14can be appropriately tailored, but is preferably a rectangular shape or a square shape. In the present embodiment, the substrate14has a square shape.

In the present embodiment, quartz glass, which is one example of glass, is adopted as a material constituting the substrate14. However, a glass constituting the substrate14is not limited to quartz glass. The glass constituting the substrate14preferably contains SiO2as a main substance. In the present embodiment, the main substance means a substance accounting for the largest content.

In addition, the material constituting the substrate14may be oxide or nitride ceramic. Examples of such a ceramic include a ceramic containing silicon oxide (SiO2) as a main substance, a ceramic made of silicon nitride (Si3N4), a ceramic made of zircon oxide (ZrO2), and a ceramic composed of a mixture of calcium silicate and lithium aluminosilicate. The ceramic composed of a mixture of calcium silicate and lithium aluminosilicate is also referred to as ADCERAM (registered trademark).

The material constituting the substrate14can be appropriately selected from the materials stated above in terms of a melting point, thermal conductivity, cost, and the like. In order to suppress the eutectic reaction that can occur at a high operating temperature, the high melting point is preferred. In order to increase energy efficiency when the plasmonic perfect absorber10(described later) is heated using Joule heat generated in the conductor layer13of the plasmonic perfect absorber10, the thermal conductivity of the substrate14is preferably lower than the conductivity of the conductor constituting the conductor layer13(described later). In order to suppress the manufacturing cost of the thermal radiation element1, it is preferable that the substrate14has a low cost.

A thickness tS(seeFIG.2) of the substrate14is preferably 100 μm or more and 10 mm or less.

For convenience of description, the substrate14is hereinafter divided into three strip-shaped regions, each of which is parallel. A central region Rcis a main region including the center of the substrate14, and is a region having the widest width (length in a left-right direction inFIGS.1and2) among the three regions. A pair of edge regions REis two regions sandwiching the central region Rc. In the present embodiment, outlines (shapes in plan view) of the central region RCand the pair of edge regions REhave all rectangular shapes. However, the outlines of the central region RCand the pair of edge regions REare not limited thereto, and can be determined as appropriate.

As illustrated inFIG.3, the plasmonic perfect absorber10included in the thermal radiation element1includes a conductor layer11, an insulator layer12, and a conductor layer13. The conductor layer11is one example of the second conductor layer, and the conductor layer13is one example of the first conductor layer. On the main surface14aof the substrate14, the conductor layer13, the insulator layer12, and the conductor layer11are laminated in this order.

The conductor layer13is a film made of a conductor formed on the main surface14awhich is one main surface (upper main surface inFIG.2) of the substrate14so as to cover the main surface14a. That is, the conductor layer13is formed over the central region Rcand the pair of edge regions RE.

In the present embodiment, hafnium nitride (HfN) is adopted as the conductor constituting the conductor layer13. However, the conductor constituting the conductor layer13is not limited to HfN, and may be any material as long as it has metallic conductive characteristics. When the plasmonic perfect absorber10is formed on a surface of the base material which is assumed to have a high temperature at the time of use, the material constituting the conductor layer13is preferably a material having a high melting point such as HfN. The melting point of HfN is typically 3330° C.

A region of the main surface14awhere the conductor layer13is formed may be the entire main surface14aor a part of the surface of the base material, and can be appropriately determined. In the present embodiment, the conductor layer13is formed on the entire main surface14a.

In the present embodiment, a thickness t13(seeFIG.2) of the conductor layer13is set to 100 nm. However, the thickness t13is not limited to 100 nm, and can be appropriately determined within a range of, for example, 10 nm to 10 μm. The thickness t13is one example of the thickness t1recited in the claims.

The insulator layer12is a film made of an insulator formed on a main surface13a(upper main surface inFIG.2) which is a main surface opposite to the substrate14among main surfaces of the conductor layer13, so as to cover at least a part of the main surface13a. In the present embodiment, as illustrated inFIG.2, the insulator layer12is laminated on the conductor layer13so as to cover the central region Rc. In the present embodiment, since the central region Rchas a rectangular outline, the conductor layer13has also a rectangular outline.

In the present embodiment, the insulator layer12which is a solid film having a uniform thickness is formed so as to cover the entire central region Rc. However, the insulator layer12may be formed only in a region encompassed in the central region Rc, where a plurality of conductor patterns111is formed. Similarly, to the conductor layer11, the insulator layer12may be composed of the plurality of conductor patterns arranged periodically, each of the plurality of insulator patterns has a circular shape or a regular polygonal shape.

In the present embodiment, SiO2is adopted as the material constituting the insulator layer12. However, the material constituting the insulator layer12may be any insulator, and is not limited to SiO2. Examples of such a material include insulating oxides. In a case where the plasmonic perfect absorber10is formed on the main surface14aof the substrate14that is assumed to have a high temperature during use, the material constituting the insulator layer12is preferably any of SiO2, aluminum oxide (Al2O3), aluminum nitride (AlN), and a mixture of SiO2and Al2O3.

In the present embodiment, a thickness t12(seeFIG.2) of the insulator layer12is set to 180 nm. However, the thickness t12is not limited to 180 nm, and can be appropriately determined within a range of, for example, 10 nm to 10 μm.

The conductor layer11is formed on a main surface12a(upper main surface inFIG.2) which is a main surface opposite to the insulator layer12among main surfaces of the insulator layer12. Similarly to the insulator layer12, the conductor layer11is laminated only in the central region Rc. Therefore, the insulator layer12and the conductor layer11are laminated in only the central region Rcin the plasmonic perfect absorber10.

The conductor layer11includes the plurality of (nine inFIG.3) conductor patterns111each having a circular shape. However, the shape of each conductor pattern111is not limited to the circular shape, and may be a regular polygonal shape. Preferable examples of the regular polygonal shape include a regular hexagonal shape.

A reference numeral111is given to only one conductor pattern111among the plurality of conductor patterns111. As illustrated inFIG.3, the plurality of conductor patterns111is two-dimensionally and periodically arranged on the main surface12a. In the present embodiment, as illustrated inFIG.3, a square arrangement is adopted as the periodic two-dimensional arrangement of the conductor patterns111. However, the periodic two-dimensional arrangement is not limited to the square arrangement, and may be, for example, a six-way arrangement.

In the cross-sectional view illustrated inFIG.2, the plurality of conductor patterns111constituting the conductor layer11are not shown. In practice, a periodic two-dimensional structure including the plurality of conductor patterns111is formed on the entire main surface12a.

In the present embodiment, hafnium nitride (HfN) is adopted as the conductor constituting each conductor pattern111of the conductor layer11. However, the conductor constituting each conductor pattern111is not limited to HfN, and may be any material as long as it has metallic conductive characteristics. The conductor constituting each conductor pattern111is the same as the conductor constituting the conductor layer13.

In the present embodiment, a thickness t11of the conductor layer11(seeFIG.2; i.e. a thickness of each conductor pattern111) is set to 100 nm. However, the thickness t13is not limited to 40 nm, and can be appropriately determined within a range of, for example, 10 nm to 10 μm. The thickness t11is one example of the thickness t2recited in the claims.

The thickness t13of the conductor layer13and the thickness t11of the insulator layer12preferably satisfy a relationship of t13>1.5× t11.

As illustrated inFIGS.1and2, a base layer131and an electrode pad132are laminated in this order on the conductor layer13in one edge region RE(a left side in the state illustrated inFIG.2). A base layer131and an electrode pad133are laminated in this order on the conductor layer13in the other edge region RE(a right side in the state illustrated inFIG.2).

The pair of base layers131and the pair of electrode pads132and133are provided in a band shape along the edge region RE. The pair of base layers131and the pair of electrode pads132and133are one example of the pair of electrodes recited in the claims.

By connecting wirings having different polarities and supplying power to each of the electrode pads132and133, a current flows from one of the electrode pads132and133to the other. That is, the current flows through the conductor layer13in the in-plane direction of the main surface13a. Therefore, the pair of base layers131and the electrode pads132and133provided on the main surface13aof the conductor layer13are one example of the electrodes that cause the current to flow in the in-plane direction of the main surface of the conductor layer13.

In the present embodiment, the pair of base layers131, elongated in a band shape, and the each of the electrode pads132and133are provided so as to sandwich the central region Rc. That is, the pair of base layers131and each of the electrode pads132and133are provided along each of the pair of opposite sides in the central region Rchaving the rectangular shape (square shape in the present embodiment).

In the present embodiment, gold is adopted as a material constituting the electrode pads132and133. However, the material is not limited to gold, and can be appropriately determined in consideration of a high conductivity, a low reactivity, a high melting point, and the like.

In the present embodiment, a two-layer film of Cr/Pt in which chromium (Cr) and platinum (Pt) are laminated in this order is used as the pair of base layers131. The thicknesses of Cr and Pt are not particularly limited, but are each 50 nm in the present embodiment. However, the pair of base layers131may have a configuration as a single layer film or a multilayer film made of three or more layers. The material of each film constituting the pair of base layers131can also be appropriately selected. The pair of base layers131can be omitted in some cases in terms of compatibility and reactivity with the material constituting the substrate14and the material constituting the electrode pads132and133.

The housing20is a rectangular parallelepiped block. In the present embodiment, a material constituting the housing20is aluminum, which is one example of metal. However, the metal constituting the housing20is not limited to aluminum, and can be appropriately selected. The material constituting the housing20is not limited to metal, and may be an alloy, an inorganic compound such as ceramic, or an organic compound such as resin. However, in a case where the operating temperature of the thermal radiation element1is set to 150° C. or higher, the material constituting the housing20is preferably any of metal, alloy, and ceramic.

Out of a pair of main surfaces of the housing20, the main surface located on an upper side in the state illustrated inFIG.1is referred to as a main surface20a, and the main surface located on a lower side in the state illustrated inFIG.1is referred to as a main surface20b. The cavity C is formed in the main surface20a. A depth of the cavity C is smaller than a thickness of the housing20. Therefore, the cavity C does not penetrate the main surface20b.

The cavity C includes two subcavities C1and C2.

The subcavity C1is formed in a region close to the main surface20a(that is, a shallow region). The subcavity C2is formed in a region farther away from the main surface20aas compared to the subcavity C1(that is, a deep region). An opening APCof the subcavity C1is determined to have a size that is able to accommodate the thermal radiation element1in plan view. A reference sign APCis clearly illustrated in the upper view ofFIG.1, but APCis omitted in the lower view ofFIG.1.

On the other hand, an opening of the subcavity C2formed on a bottom surface of the subcavity C1is determined to have a size that can be included by the thermal radiation element1in plan view. The cavity C thus configured is formed in a stepped shape.

The thermal radiation element1is accommodated in the subcavity C1of the cavity C. At least a part of the edge region REof the substrate14constituting the thermal radiation element1is fixed to a bottom wall of the subcavity C1using the bonding member31. In the present embodiment, sintered silver (Ag) is adopted as the bonding member31. The silver thus sintered has heat resistance to withstand the operating temperature of the thermal radiation element1(for example, any temperature falling within a range from 300° C. to 1200° C.), and is thus preferable as the bonding member31.

As described above, since the thermal radiation element1has a high operating temperature, in order to enhance energy efficiency, it is preferable to suppress thermal energy dissipated by heat conduction from the thermal radiation element1to the housing20. In the thermal radiation element module M, since the subcavity C2is formed in the housing20in addition to the subcavity C1, it is possible to limit a path of heat conduction that can occur between the thermal radiation element1and the housing20.

Electrode pads21and22are provided on the bottom wall of the subcavity C1so as to run in parallel with the electrode pads132and133. The electrode pad21and the electrode pad132are electrically connected by the metal wire32(see the lower view ofFIG.1). Similarly, the electrode pad22and the electrode pad133are electrically connected by the metal wire (reference numeral is omitted) (see the lower view ofFIG.1).

In the present embodiment, the electrode pads21and22are also extended in a band shape similarly to the electrode pads132and133. Since the electrode pads21and22and the electrode pads132and133are both extended in a band shape, a plurality of metal wires32can be used to conduct the electrodes. Therefore, it is possible to reduce a resistance value that can be generated between the electrode pad21and the electrode pad132and between the electrode pad22and the electrode pad133, and it is possible to ensure redundancy in a case where the electrode pads are electrically connected to each other.

As illustrated in the lower view ofFIG.1, the housing20is provided with the power terminals41and42. The power terminal41is drawn from the outside to the inside of the housing20. A tip of the power terminal41is electrically connected to the electrode pad21. Similarly, the power terminal42is drawn from the outside to the inside of the housing20. A tip of the power terminal42is electrically connected to the electrode pad22. A portion where each of the power terminals41and42is drawn to the inside of the housing20is sealed so as to maintain hermeticity.

As illustrated in the upper view and the lower view ofFIG.1, the opening APCis covered with the optical window23. A material constituting the optical window23preferably has translucency and heat resistance to withstand the operating temperature of the thermal radiation element1(for example, any temperature falling within a range from 300° C. to 1200° C.). In the present embodiment, a plate-shaped member made of quartz glass is adopted.

The optical window23is joined to the main surface20aof the housing20using the bonding member24. In the present embodiment, gold (Au)-tin (Sn) solder is used as the bonding member24.

The thermal radiation element module M is configured such that a pressure inside the cavity C is lower than a pressure (for example, atmospheric pressure) outside the cavity C. This configuration can be implemented, for example, by sealing the cavity C under a reduced pressure environment in which the pressure is lower than the atmospheric pressure. The pressure inside the cavity C is preferably, but not limited to, 1×103Pa or less. As the pressure inside the cavity C is lower, the adiabaticity of the cavity C can be enhanced.

SUMMARY

The thermal radiation element1according to one aspect of the present invention includes: the substrate14made of an insulator; and the plasmonic perfect absorber10in which the conductor layer13(first conductor layer) covering at least a part of one main surface14a(entire in the present embodiment), the insulator layer12, and the conductor layer11(second conductor layer) are laminated in this order. In the plasmonic perfect absorber10, the conductor layer13is provided with the base layer131and the electrode pads132and133which are electrodes through which the current flows in the in-plane direction of the main surface13a.

According to this configuration, the conductor layer13is used as a heat source when viewed from the plasmonic perfect absorber10. That is, the substrate14having a larger volume than that of the plasmonic perfect absorber10when viewed from the plasmonic perfect absorber10is not a heat source. Therefore, in a case where the plasmonic perfect absorber10is heated to the operating temperature, it is not necessary to heat the substrate14having a large volume to the operating temperature or higher, whereby the thermal radiation element1can enhance energy efficiency as compared with the thermal radiation element of JP 2020-64820 A which is a conventional invention.

The thermal radiation element1adopts a configuration in which the thermal conductivity of the insulator constituting the substrate14is lower than the thermal conductivity of the conductor constituting the conductor layer13.

According to this configuration, the thermal energy generated by the conductor layer13as a heat source can be suppressed from escaping to the substrate14, whereby the energy efficiency can be further enhanced.

The thermal radiation element1adopts a configuration in which the conductor layer11includes the plurality of conductor patterns111arranged two-dimensionally and periodically, each of the plurality of conductor patterns111having a circular shape or a regular polygonal shape.

According to this configuration, the wavelength range of the light emitted from the plasmonic perfect absorber10can be adjusted by adjusting the size and the periodic arrangement of the plurality of conductor patterns111.

The thermal radiation element1adopts a configuration in which the thickness t13of the conductor layer13(thickness t1 of the first conductor layer) and the thickness t11of the conductor layer11(thickness t2 of the second conductor layer) satisfy the relationship of t13>1.5× t11(t1>1.5× t2).

According to this configuration, since the resistance value of the conductor layer13is appropriately lowered, a large current easily flows through the conductor layer13. Therefore, the thermal energy generated in the conductor layer13can be increased.

The thermal radiation element1adopts a configuration in which the thickness tSof the substrate14is 100 μm or more and 10 mm or less.

According to this configuration, the strength of the substrate14supporting the plasmonic perfect absorber10can be increased to a practically sufficient strength. In this way, for allowing the substrate14to have sufficient strength, the thickness tSis significantly thicker than the total thickness of the plasmonic perfect absorber10. Therefore, the thermal radiation element1can enhance the energy efficiency more reliably than the conventional thermal radiation element.

The thermal radiation element1adopts a configuration in which the thickness t13(thickness t1 of the first conductor layer), the thickness t12of the insulator layer12(thickness td of the insulator layer), and the thickness t11(thickness t2 of the second conductor layer) are all 10 nm or more and 10 μm or less.

According to this configuration, it is possible to prevent the total thickness of the plasmonic perfect absorber10from becoming unintentionally thick and to prevent the total thickness of the plasmonic perfect absorber10from becoming thicker than the thickness tS. Therefore, the thermal radiation element1can enhance the energy efficiency more reliably than the conventional thermal radiation element.

Further, the thermal radiation element1adopts a configuration in which a region (central region Rc) where the conductor layer13(first conductor layer) is formed has a rectangular shape (i.e. square shape in the present embodiment), and the electrode includes the pair of base layers131and the pair of electrode pads132and133, corresponding to the pair of electrodes. The thermal radiation element1adopts a configuration in which each of the pair of electrodes is provided on each of the pair of opposite sides in a region having the rectangular shape (central region Rc).

According to this configuration, uniform current distribution of the current flowing in the in-plane direction of the main surface13aof the conductor layer13can be established. Since the uniform distribution of Joule heat generated in the conductor layer13can be established, the temperature distribution on the main surface13acan be made uniform approximately.

The thermal radiation element1adopts a configuration in which the substrate14is composed of glass or ceramic.

According to this configuration, since the thermal conductivity of the insulator constituting the substrate14can be reliably made lower than the thermal conductivity of the conductor constituting the conductor layer13, the thermal energy generated by the conductor layer13can be reliably suppressed from escaping to the substrate14. Therefore, the energy efficiency can be reliably enhanced.

The thermal radiation element1adopts a configuration in which the conductor layer13(first conductor layer) and the conductor layer11(second conductor layer) are made of hafnium nitride (HfN).

According to this configuration, since HfN has a high melting point, it is possible to suppress the eutectic reaction that can occur with at least one of the insulator constituting the substrate14and the insulator constituting the insulator layer12. Therefore, the operating temperature of the thermal radiation element1can be increased.

The thermal radiation element1adopts a configuration in which the insulator layer12is made of at least one of SiO2, Al2O3, and AlN.

According to this configuration, the insulator layer12having high insulating properties can be easily formed.

The thermal radiation element module M according to one aspect of the present invention includes the thermal radiation element1; and the housing20provided with the cavity C that houses the thermal radiation element1and the power terminals41and42that supply power to the pair of base layers131and the pair of electrode pads132and133, corresponding to the electrodes. In the thermal radiation element module M, at least a part of the substrate14is fixed to the cavity C using the bonding member31inside the cavity C.

The thermal radiation element module M has the same advantageous effect as that of the thermal radiation element1. The thermal radiation element constituting the thermal radiation element module M is not limited to the thermal radiation element1, and may be a thermal radiation element1A illustrated inFIG.4or a thermal radiation element1B illustrated inFIG.5. The thermal radiation elements1A and1B will be described later.

Thermal radiation element module M adopts a configuration in which the opening APCof the cavity C includes the thermal radiation element1in plan view of the opening APC(see the upper view ofFIG.1), the opening APCis sealed by the optical window23having translucency, and the pressure inside the cavity C is lower than the pressure outside the cavity C.

According to this configuration, since the adiabaticity of the cavity C can be enhanced as compared with a case where the pressure inside the cavity C is equal to or higher than the pressure outside the cavity C, the thermal energy generated by the conductor layer13can be reduced from being dissipated to the outside of the cavity C. Therefore, the energy efficiency of the entire thermal radiation element module M can also be enhanced.

Additionally, the thermal radiation element module M emits electromagnetic waves (in particular, at least one of visible light, near-infrared light, mid-infrared light, and far-infrared light) caused by thermal radiation by heating the thermal radiation element1to the predetermined operating temperature using the thermal energy. As described above, the thermal radiation element module M functions as a thermal radiation light source that emits electromagnetic waves of at least one of visible light, near-infrared light, mid-infrared light, and far-infrared light. That is, the thermal radiation light source including the thermal radiation element module M is also included in the scope of the present invention.

The advantageous effect achieved by one aspect of the present invention has been described using the thermal radiation element1illustrated inFIGS.1and2. The advantageous effect of the thermal radiation element1described above can be similarly obtained in the thermal radiation elements1A and1B described later.

Modified Example 1

The thermal radiation element1A as Modified Example 1 of the thermal radiation element1will be described with reference toFIG.4.FIG.4is a cross-sectional view of the thermal radiation element1corresponding toFIG.2, and is a cross-sectional view of the thermal radiation element1A.

The thermal radiation element1A is obtained by replacing the pair of base layers131and the electrode pads132and133included in the thermal radiation element1with a pair of base layers131A and electrode pads132A and133A. Therefore, in the present modified example, the pair of base layers131A and the electrode pads132A and133A will be described.

In the thermal radiation element1, the electrode pads132and133have a width (length in the left-right direction inFIG.2) narrower than a width of the annular edge region RE. Therefore, as illustrated inFIG.2, the electrode pads132and133are formed so as to cover a part of the edge region REin one cross section of the thermal radiation element1.

Meanwhile, in the thermal radiation element1A, the pair of base layers131A and the electrode pads132A and133A have a width (length in the left-right direction inFIG.4) equivalent to the width of the annular edge region RE. Therefore, as illustrated inFIG.4, the pair of base layers131A and the electrode pads132A and133A are formed so as to cover the entire edge region REin one cross section of the thermal radiation element1A.

As is apparent from the electrode pads132and133and the electrode pads132A and133A, the width of the pair of electrode pads for causing the current to flow through the conductor layer13can be appropriately determined, and may be electrically connected to a part of the conductor layer11in addition to the conductor layer13. The same applies to the pair of base layers131A. In the thermal radiation element1A, a part of the vicinity of upper ends of the electrode pads132A and133A may overlap an outer edge portion of the conductor layer11.

Modified Example 2

The thermal radiation element1B as Modified Example 2 of the thermal radiation element1will be described with reference toFIG.5.FIG.5is a cross-sectional view of the thermal radiation element1corresponding toFIG.2, and is a cross-sectional view of the thermal radiation element1B.

The thermal radiation element1B is obtained by replacing the insulator layer12, the conductor layer11, the pair of base layers131, and the electrode pads132and133included in the thermal radiation element1with an insulator layer12B, a conductor layer11B, a pair of base layers131B, and electrode pads132B and133B, respectively. Therefore, in the present modified example, the insulator layer12B, the conductor layer11B, the pair of base layers131B, and the electrode pads132B and133B will be described.

In the thermal radiation element1, the insulator layer12and the conductor layer11are formed so as to cover the central region Rcof the main surface13aof the conductor layer13.

Meanwhile, in the thermal radiation element1B, the insulator layer12B and the conductor layer11B are formed so as to cover the entire main surface13aof the conductor layer13.

In addition, as illustrated inFIG.5, the pair of base layer131B and the electrode pads132B and133B are formed so as to cover side surfaces of the substrate14, the conductor layer13, the insulator layer12B, and the conductor layer11B (that is, side surfaces of the thermal radiation element1B) in one cross section of the thermal radiation element1B. One base layer131B and the electrode pad132B are laminated in this order on one side surface (side surface on the left side inFIG.5) of the thermal radiation element1B, and the other base layer131B and the electrode pad1338are laminated in this order on a side surface (side surface on the right side inFIG.5) facing the side surface stated above.

In the thermal radiation element1B, a part in the vicinity of lower ends of the pair of base layers131B and the electrode pads132B and133B is also formed in a region in the vicinity of an edge of the main surface14bwhich is a lower main surface of the substrate14. In the thermal radiation element1B, the pair of base layers131B and the electrode pads132B and133B formed in a region in the vicinity of the edge of the main surface14bare joined to the electrode pads21and22using the bonding member31(see the lower view ofFIG.1). As described above, in the present modified example, the bonding member31fixes the thermal radiation element1B to a bottom wall of the subcavity C1inside the cavity C, and ensures conduction between the electrode pads132B and133B and the electrode pads21and22.

Similarly to the pair of base layers131and the pair of base layers131A, the pair of base layers131B may be a single layer film, a two-layer film, or a multilayer film made of at least three layers. Each film constituting the pair of base layers131B can be configured in the same manner as each film constituting the pair of base layers131and the pair of base layers131A.

EXAMPLES

First Example

The thermal radiation element module M according to a first example of the present invention will be described below. In the present example, the configuration of the thermal radiation element1A illustrated inFIG.4is adopted as the thermal radiation element, and each component is designed as follows. In the thermal radiation element module M of this example, it has been confirmed that, in a case where 500° C. is adopted as one example of the operating temperature of the thermal radiation element1A, near-infrared light of 1.0 μm or more and 2.0 μm or less is stably emitted. That is, the thermal radiation element module M of this example can be suitably used as a thermal radiation light source that stably emits near-infrared light of 1.0 μm or more and 2.0 μm or less when 500° C. is adopted as the operating temperature.

As the substrate14, a plate-shaped member made of quartz glass, having the thickness tSof 500 μm and the square shape with a side length of 5 mm is used.

An HfN film having the thickness t13of 100 nm is used as the conductor layer13.

As the insulator layer12, an SiO2film having the thickness t12of 180 nm is used.

An HfN film having the thickness t11of 40 nm is used as the conductor layer11. In addition, as shapes of the plurality of conductor patterns111constituting the conductor layer11, a circular shape having a diameter of 400 nm is adopted. As the periodic arrangement of the plurality of conductor patterns111, a square arrangement having a period of 650 nm is adopted.

As the pair of base layers131A, a two-layer film of Cr/Pt is used. The thickness of each of Cr and Pt is 50 nm.

As the electrode pads132A and133A, a band-shaped gold film having a thickness of 400 nm, a width (length in the left-right direction inFIG.4) of 200 μm, and a length (length in the depth direction inFIG.4) of 5 mm is adopted.

The electrical resistivity of HfN adopted in this example is about 1×103(Ω·mm), and the electrical resistivity of SiO2adopted in this example is about 1×105(Ω·mm). In the thermal radiation element1A of this example, the plasmonic perfect absorber10A has a thickness of 220 nm in total.

A gold wire having a diameter φ of 25 μm is used as the metal wire32that electrically connects the electrode pad21and the electrode pad132and the metal wire (see the lower view ofFIG.1) that electrically connects the electrode pad22and the electrode pad133.

As the pressure inside the cavity C, 1×100 Pa is employed.

Second Example

The thermal radiation element module M according to a second example of the present invention will be described below. In the present example, the configuration of the thermal radiation element1B illustrated inFIG.5is adopted as the thermal radiation element, and each component is designed as follows. In the thermal radiation element module M of this example, it has been confirmed that, in a case where 700° C. is adopted as one example of the operating temperature of the thermal radiation element1B, near-infrared light of 1.0 μm or more and 2.0 μm or less is stably emitted. That is, the thermal radiation element module M of this example can be suitably used as a thermal radiation light source that has the operating temperature of 700° C. and stably emits near-infrared light of 1.0 μm or more and 2.0 μm or less.

As the substrate14, a plate-shaped member made of quartz glass, having the thickness tSof 500 μm and the square shape with a side length of 10 mm is used.

An HfN film having the thickness t13of 200 nm is used as the conductor layer13.

As the insulator layer12, an SiO2film having the thickness t12of 320 nm is used.

An HfN film having the thickness t11of 40 nm is used as the conductor layer11. In addition, shapes of the plurality of conductor patterns111constituting the conductor layer11are the same as the shapes of the plurality of conductor patterns111adopted in the first example.

As the pair of base layers131B, a two-layer film of Cr/Pt is adopted. The thickness of Cr is 100 nm, and the thickness of Pt is 200 nm.

As the electrode pads132B and133B, a gold film having a thickness (length in the left-right direction inFIG.5) of 500 nm is used. On one side surface of the substrate14and the plasmonic perfect absorber10B, one base layer131B and an electrode pad132B are laminated in this order on the entire surface, and on a side surface facing the one side surface, the other base layer131B and the electrode pad133B are laminated in this order on the entire surface.

The electrical resistivity of HfN adopted in this example is about 1×10−3(Ω·mm), and the electrical resistivity of SiO2adopted in this example is about 1×1015(Ω·mm). In the thermal radiation element1B of this example, the plasmonic perfect absorber10B has a thickness of 580 nm in total.

In this example, sintered silver is used as the bonding member31that bonds and conducts the one base layer131B and a part of the electrode pad132B (part in the vicinity of a lower end in the state shown inFIG.5) and the electrode pad21, and the bonding member31that bonds and conducts the other base layer131B and a part of the electrode pad133B (part in the vicinity of the lower end in the state shown inFIG.5) and the electrode pad22.

As the pressure inside the cavity C, 1×100 Pa is employed.

ADDITIONAL REMARKS

The present invention is not limited to the embodiments stated above, and various modifications can be made within the scope defined in claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.