JP7786019B2 - Nitride insulating material, its manufacturing method, and heat flow switching element and thermoelectric conversion element - Google Patents

Description

The present invention relates to a nitride insulating material with low lattice thermal conductivity, a method for manufacturing the same, and a heat flow switching element and a thermoelectric conversion element.

Conventionally, as a heat flow switch that actively changes the thermal conductivity by a bias voltage, for example, Non-Patent Document 1 proposes a heat flow switching element in which an electrically insulating polyimide tape is sandwiched between two sheets of semiconductor material: Ag ₂ S _0.6 Se _0.4 , and the thermal conductivity is changed by applying an electric field.

Takuya Matsunaga and four others, "Fabrication of a heat flow switching element operated by bias voltage," 15th Annual Meeting of the Thermoelectric Society of Japan, September 13, 2018

The above conventional techniques still have the following problems.
In the technology described in Non-Patent Document 1, applying a voltage generates thermally conductive charges at the interface between a semiconductor material and an insulating material, which can transport heat. This allows for an immediate transition to a changed thermal conductivity state, resulting in relatively good thermal response. However, in order to change the thermal conductivity at the material interface in response to this external electric field (external voltage) and increase the change in thermal conductivity of the entire device, it is necessary to reduce the inherent thermal conductivity of the material that constitutes the device at zero bias. Thermal conductivity is a function proportional to the square of the thermal effusivity, so it is necessary to reduce the inherent thermal effusivity of the material that constitutes the device at zero bias. The inherent thermal conductivity of a material at zero bias is expressed as the sum (addition) of the lattice thermal conductivity and the electronic thermal conductivity.
Thermal conductivity = lattice thermal conductivity + electronic thermal conductivity

Lattice thermal conduction is heat conduction due to vibrations (phonons, lattice vibrations) that travel between crystal lattices. Electronic thermal conduction is heat conduction due to conduction electrons, and generally, electronic thermal conductivity tends to increase as electrical conductivity increases. Regarding the electronic thermal conductivity of semiconductors, in order to maintain the semiconductor's electrical conductivity, the material's inherent electronic thermal conductivity at zero bias must be adjusted to an appropriate value without increasing the total thermal conduction. Note that insulator materials do not have electronic thermal conduction. On the other hand, a lower lattice thermal conductivity is preferable. Materials with low lattice thermal conductivity can reduce the overall thermal conductivity of the device at zero bias, thereby increasing the rate of change in interface-induced thermal conductivity in response to an external electric field and improving the overall heat flow switching performance of the device. Therefore, there is a demand for the use of low thermal conductivity (low thermal permeability) semiconductor and insulator materials due to their low lattice thermal conductivity. Furthermore, the use of nitride materials as constituent materials is desirable to improve the heat resistance of heat flow switching devices.
Furthermore, in a thermoelectric conversion element, it is desirable to use an insulating material with low lattice thermal conductivity and high thermal insulation performance in order to suppress heat release from the surface of the thermoelectric conversion part and ensure a sufficient temperature difference between the high-temperature side and the low-temperature side.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a nitride insulator material with low lattice thermal conductivity, a method for manufacturing the same, and a heat flow switching element and a thermoelectric conversion element.

The present invention employs the following configuration to solve the above problems: Namely, the nitride insulator material according to the first invention is a metal nitride represented by M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element), and is characterized by being a nanocrystal.
This nitride insulator material is a metal nitride represented by the formula M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element), and is a nanocrystal, so it has insulating properties and low lattice thermal conductivity, resulting in low thermal conductivity and low thermal effusivity. Therefore, the nitride insulator material of the present invention is suitable as an electrical and thermal barrier material.
Among the constituent elements, M (at least one of Ta and Hf) and Si are nanocrystallized (crystal size is 5 nm or less, including amorphous), which reduces the lattice thermal conductivity and makes it possible to reduce the thermal effusivity. Furthermore, the content of N among the constituent elements provides insulation. Furthermore, Te among the constituent elements has the effect of further reducing the thermal effusivity.
The expression "Te is an optional element" indicates that the inclusion of Te (tellurium) is optional. In other words, it indicates that Te may or may not be included. In other words, it is M-Si-N or M-Si-N-Te (wherein M represents at least one transition metal element).

A nitride insulating material according to a second invention is the nitride insulating material of the first invention, characterized in that it has a thermal effusivity of less than 2000 Ws ^0.5 /m ² K.
That is, this nitride insulating material has a thermal effusivity of less than 2000 Ws ^0.5 /m ² K, and therefore has a thermal conductivity lower than that of HfO ₂ .
The thermal effusivity is preferably 100 Ws ^0.5 /m ² K or more.

A nitride insulating material according to a third invention is the nitride insulating material of the second invention, characterized in that it has a thermal effusivity of less than 1700 Ws ^0.5 /m ² K.
That is, this nitride insulator material has a thermal effusivity of less than 1700 Ws ^0.5 /m ² K, and therefore has a thermal conductivity lower than that of HfO ₂ or SiN. This nitride insulator material exhibits lower thermal conductivity, i.e., higher thermal insulation, and is therefore more suitable as an insulator layer that constitutes a heat flow switching element and an insulator layer that constitutes a thermoelectric conversion element.

A nitride insulating material according to a fourth invention is the nitride insulating material according to any one of the first to third inventions, characterized in that it has an electrical resistivity of 10 ⁸ Ωcm or more.
That is, since this nitride insulator material has an electrical resistivity of 10 ⁸ Ωcm or more, an insulating property is obtained in which a current of less than 100 μA/mm ² flows in the film thickness direction when a voltage of 10 V is applied in the film thickness direction for a nitride insulator material with a film thickness of 100 nm.

A nitride insulating material according to a fifth invention is characterized in that, in any one of the first to fourth inventions, it is used as a low thermal conductive material.
That is, this nitride insulating material has a low thermal effusivity and is therefore suitable as a low thermal conductive insulating material for use in heat flow switching elements, thermoelectric conversion elements, and the like.

A heat flow switching element according to a sixth aspect of the present invention comprises an N-type semiconductor layer, an insulator layer stacked on the N-type semiconductor layer, and a P-type semiconductor layer stacked on the insulator layer, wherein the insulator layer is formed from any one of the nitride insulator materials according to the first to fifth aspects of the present invention.
That is, this heat flow switching element comprises an N-type semiconductor layer, an insulator layer stacked on the N-type semiconductor layer, and a P-type semiconductor layer stacked on the insulator layer, so when an external voltage is applied to the N-type semiconductor layer and the P-type semiconductor layer, electric charges are induced mainly at the interfaces between the P-type semiconductor layer and the N-type semiconductor layer and the insulator layer, and these electric charges carry heat, causing a change in thermal conductivity.
In particular, since the insulator layer is formed from any of the nitride insulator materials of the first to third inventions, the insulating layer has low lattice thermal conductivity, resulting in low lattice thermal conductivity and low thermal effusivity, and the rate of change of thermal conductivity can be increased by an external electric field (external voltage).
Furthermore, when the N-type semiconductor layer and the P-type semiconductor layer are made of nitride, the insulator layer is also made of nitride, which improves the bonding strength at the interfaces between the P-type semiconductor layer and the insulator layer and between the N-type semiconductor layer and the insulator layer.

The rate of increase Δk of thermal conductivity after voltage application, which is the performance of the heat flow switch, is evaluated by the following formula.
Δk=k(V)/k(0)-1
Δk=b(V) ² /b(0) ² -1
k (V): Thermal conductivity when voltage is applied (W/mK)
k(0): Thermal conductivity without voltage application (W/mK)
b (V): Thermal effusivity when voltage is applied (Ws ^0.5 /m ² K)
b(0): Thermal effusivity without voltage application (Ws ^0.5 /m ² K)
The thermal conductivity due to the interface, which changes with the above-mentioned external voltage, is defined as the "third thermal conductivity" and is conveniently distinguished from the thermal conductivity inherent to the material (the sum of the lattice thermal conductivity and the electronic thermal conductivity), which does not change with the external voltage.

k(V) = electronic thermal conductivity of semiconductor + lattice thermal conductivity of semiconductor + lattice thermal conductivity of insulator + third thermal conductivity k(0) = electronic thermal conductivity of semiconductor + lattice thermal conductivity of semiconductor + lattice thermal conductivity of insulator. To improve heat flow switch performance, it is preferable to select a material with low electronic thermal conductivity and lattice thermal conductivity. Regarding the electronic thermal conductivity of the semiconductor, in order to maintain the conductivity of the semiconductor, the electronic thermal conductivity inherent to the material at zero bias must be adjusted to an appropriate value so as not to increase the total thermal conductivity. On the other hand, regarding lattice thermal conductivity, a material with low lattice thermal conductivity can reduce k(0) and reduce the thermal conductivity of the entire element at zero bias. Therefore, the lower the lattice thermal conductivity, the greater the contribution of electronic thermal conductivity in response to an external electric field from zero bias. This increases the rate of change of thermal conductivity in response to the external electric field, improving heat flow switch performance.

Furthermore, since charges are generated both at and near the interface between the N-type semiconductor layer and the insulator layer, and at and near the interface between the P-type semiconductor layer and the insulator layer, a large amount of charges is generated, resulting in a large change in thermal conductivity and high thermal responsiveness. Furthermore, since this is a mechanism that physically changes thermal conductivity without using a chemical reaction mechanism, it is possible to immediately transition to a state where thermal conductivity has changed, and good thermal responsiveness can be obtained.
Furthermore, since the amount of charge induced at the interface varies depending on the magnitude of the external voltage, it is possible to adjust the thermal conductivity by adjusting the external voltage, making it possible to actively control the heat flow through this element.
Furthermore, since the insulating layer is an insulator and no current is generated when a voltage is applied, no Joule heat is generated, making it possible to actively control the heat flow without self-heating.

The heat flow switching element according to a seventh invention is the sixth invention, characterized in that it comprises an upper high thermal conductivity portion provided on the top surface, a lower high thermal conductivity portion provided on the bottom surface, and a peripheral heat insulation portion provided to cover the outer edges of the N-type semiconductor layer, the insulator layer, and the P-type semiconductor layer, and the peripheral heat insulation portion is formed from the nitride insulator material having lower thermal conductivity than the upper high thermal conductivity portion and the lower high thermal conductivity portion.
In other words, in this heat flow switching element, the peripheral heat insulating portion is formed of the nitride insulator material, which has lower thermal conductivity than the upper high thermal conductivity portion and the lower high thermal conductivity portion, so that the heat flow in the in-plane direction can be suppressed and heat flow switching ability can be obtained in the stacking direction. In particular, when an N-side electrode and a P-side electrode are disposed on the periphery of each layer, the flow of heat into these electrodes can be suppressed as much as possible by the peripheral heat insulating portion, which has low thermal conductivity.

A thermoelectric conversion element according to an eighth aspect of the present invention comprises an insulating base material, a P-type thermoelectric conversion unit and an N-type thermoelectric conversion unit formed on the insulating base material, a connection electrode unit connecting the P-type thermoelectric conversion unit and the N-type thermoelectric conversion unit, and an insulator covering surfaces of the P-type thermoelectric conversion unit and the N-type thermoelectric conversion unit, wherein the insulator is formed from a nitride insulator material according to any one of claims 1 to 5.
In other words, in this thermoelectric conversion element, the insulator is formed from any one of the nitride insulator materials of the first to fifth inventions, and since the surface of the thermoelectric conversion part is covered with an insulator made of a nitride insulator material with low thermal conductivity, heat release from the surface of the thermoelectric conversion part is suppressed, and a sufficient temperature difference between the high-temperature side and the low-temperature side can be ensured.
Furthermore, when the P-type thermoelectric conversion section and the N-type thermoelectric conversion section are nitrides, the insulator is also nitride, which improves the bonding strength at the interfaces between the P-type semiconductor layer and the N-type semiconductor layer and the insulator layer.

A thermoelectric conversion element according to a ninth invention is the thermoelectric conversion element of the eighth invention, characterized in that the P-type thermoelectric conversion portion, the N-type thermoelectric conversion portion, and the insulator are in the form of films.
That is, in this thermoelectric conversion element, the P-type thermoelectric conversion portion, the N-type thermoelectric conversion portion, and the insulator are in the form of films, so that the entire element can be made thinner.

A tenth aspect of the present invention is a method for producing a nitride insulator material according to any one of the first to fifth aspects of the present invention, characterized in that a film is formed by reactive sputtering in a nitrogen-containing atmosphere using an M-Si-Te sputtering target (wherein M represents at least one of Ta and Hf, and Te is an optional element).
That is, in this method for producing a nitride insulator material, a M-Si-Te sputtering target (where M represents at least one of Ta and Hf, and Te is an optional element) is used to perform reactive sputtering in a nitrogen-containing atmosphere to form a film, and therefore it is possible to obtain a nitride insulator layer or nitride insulator film that is a metal nitride represented by the formula M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element), is nanocrystalline, and has small surface roughness.

According to the present invention, the following effects are achieved.
That is, the nitride insulator material of the present invention is a metal nitride represented by the formula M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element), and is in the form of a nanocrystal, so that it has insulating properties and low lattice thermal conductivity, thereby achieving low thermal conductivity with a low thermal effusivity. Therefore, the nitride insulator material of the present invention is suitable as an electrical and thermal barrier material (an insulating material and a heat insulating material).
Furthermore, in the heat flow switching element of the present invention, the insulating layer is formed from the nitride insulator material of the present invention, and the insulating layer has low lattice thermal conductivity, which increases the rate of change of thermal conductivity in response to an external electric field, thereby improving heat flow switching performance.
Furthermore, in the thermoelectric conversion element of the present invention, the insulator is formed from the nitride insulator material of the present invention, and the insulator has low lattice thermal conductivity, which suppresses heat release from the surface of the thermoelectric conversion part, thereby ensuring a sufficient temperature difference between the high-temperature side and the low-temperature side.

1 is a perspective view showing a heat flow switching element in a first embodiment of a nitride insulating material, a manufacturing method thereof, and a heat flow switching element according to the present invention; FIG. 2 is a conceptual diagram for explaining the principle of a heat flow switching element in the first embodiment. FIG. 10 is a cross-sectional view showing a heat flow switching element in a second embodiment of the nitride insulator material, its manufacturing method, and heat flow switching element according to the present invention. FIG. 10 is a perspective view showing a thermoelectric conversion element in a third embodiment of the nitride insulator material, the manufacturing method thereof, and the thermoelectric conversion element according to the present invention. FIG. 10 is a cross-sectional view showing a thermoelectric conversion element in a fourth embodiment of the nitride insulator material, the manufacturing method thereof, and the thermoelectric conversion element according to the present invention. FIG. 1 is an explanatory diagram showing the layout of an insulation evaluation test in an embodiment of a nitride insulator material and a manufacturing method thereof, as well as a heat flow switching element and a thermoelectric conversion element according to the present invention. 1 is a graph showing an XRD pattern in an example according to the present invention. 1 is a cross-sectional SEM image in an embodiment according to the present invention. 1A and 1B are cross-sectional SEM images showing Example 7(a) and Example 25(b) in examples according to the present invention. 1A and 1B are TEM images showing Example 7(a) and Example 25(b) in examples according to the present invention. 10A and 10B are diffraction pattern images showing Example 7(a) and Example 25(b) in examples according to the present invention.

A first embodiment of a nitride insulating material, a manufacturing method thereof, a heat flow switching element, and a thermoelectric conversion element according to the present invention will be described below with reference to Figures 1 and 2. Note that the scale of the drawings used in the following description has been changed as necessary to make each part recognizable or easily recognizable.

As shown in FIGS. 1 and 2 , the heat flow switching element 1 of this embodiment includes an N-type semiconductor layer 3, an insulator layer 4 stacked on the N-type semiconductor layer 3, and a P-type semiconductor layer 5 stacked on the insulator layer 4.
Furthermore, the heat flow switching element 1 of this embodiment includes an N-side electrode 6 connected to the N-type semiconductor layer 3 and a P-side electrode 7 connected to the P-type semiconductor layer 5 .

The insulator layer 4 is a nitride insulator material with low thermal conductivity, which is a metal nitride represented by M-Si-N-Te (wherein M represents at least one of Ta and Hf, and Te is an optional element), and is a nanocrystal.
In this specification, if the crystal size is 5 nm or less, it is called nanocrystal, including amorphous materials.
The crystal size was determined by randomly selecting 10 crystals in a cross-sectional TEM image and averaging their equivalent circle diameters.

The insulator layer 4 is a metal nitride represented by M-Si-N-Te (wherein M represents at least one of Ta and Hf, and Te is an optional element), and the metal nitride is Ta-Si-N, Hf-Si-N, Ta-Hf-Si-N, or Ta-Si-N-Te.
Furthermore, the N-type semiconductor layer 3 and the P-type semiconductor layer 5 are made of a nitride semiconductor material with low thermal conductivity, for example, a metal nitride represented by A-Si-N-Te (where A represents at least one transition metal element, and Te is an optional element), and are nanocrystals.
That is, the metal nitrides include Cr—Si—N, Mn—Si—N, Ni—Si—N, Mo—Si—N, W—Si—N, Cr—W—Si—N, Cr—Si—N—Te, and W—Si—N—Te.

These films are formed by various methods such as sputtering and molecular beam epitaxy (MBE).
In the sputtering method, the above metal nitride can be deposited in a sputtering apparatus using targets of various composition ratios in an atmosphere of a mixed gas of Ar gas and nitrogen gas, while varying the sputtering gas pressure, nitrogen gas partial pressure, etc.
In this embodiment, an M-Si-Te sputtering target (wherein M represents at least one of Ta and Hf, and Te is an optional element) is used to perform reactive sputtering in a nitrogen-containing atmosphere to form the insulator layer 4, which is a nitride semiconductor material.
It is acceptable for the film to contain a small amount of O (oxygen) as an inevitable impurity during film formation.
Furthermore, if a voltage can be applied directly to the N-type semiconductor layer 3 and the P-type semiconductor layer 5, the N-side electrode 6 and the P-side electrode 7 are not necessary.

The heat flow switching element 1 of this embodiment also includes an insulating substrate 2, on which an N-side electrode 6 is formed. That is, the N-side electrode 6, N-type semiconductor layer 3, insulator layer 4, P-type semiconductor layer 5, and P-side electrode 7 are stacked in this order on the substrate 2. Note that the stacking order on the substrate 2 may be reversed. Furthermore, the substrate 2 itself may serve as the P-side electrode 7 or N-side electrode 6.

An external power source V is connected to apply a voltage to the N-side electrode 6 and the P-side electrode 7. The arrows in Fig. 1 indicate the direction in which the voltage (electric field) is applied.
The N-type semiconductor layer 3 and the P-type semiconductor layer 5 are formed as thin films with a thickness of less than 1 μm. In particular, since the charges e (positive charges and negative charges) generated at the interface with the insulator layer 4 and in the vicinity thereof are mainly accumulated in a thickness range of 5 to 10 nm, it is more preferable that the N-type semiconductor layer 3 and the P-type semiconductor layer 5 be formed with a film thickness of 100 nm or less. It is preferable that the N-type semiconductor layer 3 and the P-type semiconductor layer 5 have a film thickness of 5 nm or more.
The insulator layer 4 preferably has a thickness of 40 nm or more, which is set to a thickness that does not cause dielectric breakdown. Note that if the insulator layer 4 is too thick, it becomes difficult to transport the charge e, so the thickness is preferably less than 1 μm.

2, the type of charge e generated at the interface between the N-type semiconductor layer 3 and the insulator layer 4 and in the vicinity thereof is an electron, represented by a white circle. Also, the type of charge e generated at the interface between the P-type semiconductor layer 5 and the insulator layer 4 and in the vicinity thereof is a hole, represented by a black circle. (A hole is a hole created by a lack of electrons in the valence band of the semiconductor, and appears to have a relatively positive charge.)
The N-type and P-type of the N-type semiconductor layer 3 and the P-type semiconductor layer 5 are determined by the content of N (nitrogen). Note that the N-type and P-type can also be set by adding a metal element indicating the N-type or P-type as a dopant to the nitride insulator material.
The base material 2 may be, for example, a glass substrate.
The N-side electrode 6 and the P-side electrode 7 are made of a metal such as Mo or Al.

As shown in Figure 2, the heat flow switching element 1 of this embodiment generates thermally conductive charges e at and near the interface between the N-type semiconductor layer 3 and the insulator layer 4 when an electric field (voltage) is applied. The generated charges e carry heat, causing a change in thermal conductivity.

In order to obtain a larger change in thermal conductivity due to the charges generated at the interface and its vicinity by the application of an electric field (voltage), a material with low lattice thermal conductivity is suitable, and the nitride insulator material of this embodiment is a material with low lattice thermal conductivity, i.e., low thermal conductivity.
Furthermore, the third thermal conductivity defined above increases in accordance with the amount of electric charge e generated in response to the applied external electric field (voltage).
Since electric charge e is generated at the interfaces between the N-type semiconductor layer 3 and the P-type semiconductor layer 5 and the insulator layer 4, the amount of electric charge e generated can be increased by increasing the total area of the interfaces.

The thermal conductivity is measured, for example, by the pulsed light heating thermoreflectance method, which involves instantaneously heating a thin film sample formed on a substrate with a pulsed laser and measuring the rate of surface temperature decrease or increase due to thermal diffusion into the thin film to determine the thermal diffusivity or thermal effusivity of the thin film in the film thickness direction. Among the pulsed light heating thermoreflectance methods, the method of directly measuring thermal diffusivity (rear heating/surface temperature measurement (RF) method) requires the use of a transparent substrate through which the pulsed laser can pass. Therefore, if the substrate is not transparent, the thermal conductivity is measured using the surface heating/temperature measurement (FF) method, which measures the thermal effusivity and converts it into thermal conductivity. This measurement requires a metal film, such as Mo or Al.
In this embodiment, the thermal effusivity is measured by the surface heating/temperature measurement (FF) method.

In the heat flow switching element 1 of this embodiment, charge e is generated both at and near the interface between the N-type semiconductor layer 3 and the insulator layer 4, and at and near the interface between the P-type semiconductor layer 5 and the insulator layer 4. This generates a large amount of charge, resulting in a large change in thermal conductivity and high thermal response. Furthermore, because the mechanism physically changes thermal conductivity without using a chemical reaction mechanism, the element can immediately transition to a changed state of thermal conductivity, resulting in good thermal response.

Furthermore, since the amount of charge induced at the interface varies depending on the magnitude of the external voltage, it is possible to adjust the thermal conductivity by adjusting the external voltage, making it possible to actively control the heat flow through this element.
Since the insulating layer 4 is an insulator and no current is generated when a voltage is applied, no Joule heat is generated, making it possible to actively control the heat flow without self-heating.
Furthermore, when the N-type semiconductor layer 3 and the P-type semiconductor layer 5 are made of nitride, the insulator layer 4 is also made of nitride, which improves the bonding strength at the interfaces between the P-type semiconductor layer and the insulator layer and between the N-type semiconductor layer and the insulator layer.

As described above, the nitride insulator material (insulator layer 4) of this embodiment is a metal nitride represented by M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element), and is a nanocrystal, so it has insulating properties and low lattice thermal conductivity, resulting in low thermal conductivity with a low thermal effusivity. Therefore, the insulator layer 4 of this embodiment functions as both an electrical and thermal barrier layer.
Among the constituent elements, M (at least one of Ta and Hf) and Si are nanocrystallized (crystal size is 5 nm, including amorphous), which reduces the lattice thermal conductivity and makes it possible to reduce the thermal effusivity. Furthermore, the content of N among the constituent elements provides insulation. Furthermore, Te among the constituent elements has the effect of further reducing the thermal effusivity.

In particular, the nitride insulator material of this embodiment has a thermal effusivity of less than 2000 Ws ^0.5 /m ² K and an electrical resistivity of 10 ⁸ Ω cm or more. Therefore, the nitride insulator material of this embodiment has a thermal conductivity lower than that of HfO ₂ and exhibits insulation properties such that only a current of less than 100 μA/mm ² flows when a voltage of 10 V is applied.
Furthermore, some nitride insulator materials of this embodiment can achieve a thermal effusivity of less than 1700 Ws ^0.5 /m ² K and an electrical resistivity of 10 ⁸ Ωcm or more. Therefore, such nitride insulator materials can achieve lower thermal conductivity than HfO ₂ or SiN, and can achieve insulation such that only a current of less than 100 μA/mm ² flows when a voltage of 10 V is applied. The nitride insulator material of this embodiment exhibits lower thermal conductivity, i.e., higher thermal insulation, and is therefore more suitable as an insulator layer that constitutes a heat flow switching element and as an insulator layer that constitutes a thermoelectric conversion element.

The heat flow switching element 1 of this embodiment comprises an N-type semiconductor layer 3, an insulator layer 4 laminated on the N-type semiconductor layer 3, and a P-type semiconductor layer 5 laminated on the insulator layer 4. When an external voltage is applied to the N-type semiconductor layer 3 and the P-type semiconductor layer 5, electric charge e is induced mainly at the interfaces between the P-type semiconductor layer 5 and the N-type semiconductor layer 3 and the insulator layer 4, and this electric charge e carries heat, causing a change in thermal conductivity.

In particular, because the insulator layer 4 is formed from the above-mentioned nitride insulator material, it has low thermal conductivity, exhibiting low lattice thermal conductivity and low thermal effusivity at zero bias, and the rate of change of thermal conductivity can be increased by an external electric field (external voltage). In other words, the lower the lattice thermal conductivity, the greater the contribution of interface-induced thermal conductivity in response to an external electric field from zero bias, and the greater the rate of change of thermal conductivity in response to an external electric field, improving heat flow switch performance.

In the manufacturing method for the nitride insulator material (insulator layer 4) of this embodiment, a M-Si-Te sputtering target (where M represents at least one of Ta and Hf, and Te is an optional element) is used to form the film by reactive sputtering in a nitrogen-containing atmosphere. This makes it possible to obtain a metal nitride of the formula M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element), a nanocrystalline nitride insulator layer or nitride insulator film with low surface roughness.

Next, second and third embodiments of the nitride insulating material and its manufacturing method, as well as the heat flow switching element and thermoelectric conversion element according to the present invention, will be described below with reference to Figures 3 and 4. In the following description of each embodiment, the same components as those described in the above embodiments will be designated by the same reference numerals, and their description will be omitted.

The second embodiment differs from the first embodiment in that, in the first embodiment, one N-type semiconductor layer 3, one insulator layer 4, and one P-type semiconductor layer 5 are laminated, whereas in the heat flow switching element 21 of the second embodiment, multiple N-type semiconductor layers 23 and multiple P-type semiconductor layers 25 are laminated alternately with an insulator layer 24 sandwiched therebetween, as shown in FIG. 3 .
That is, in the second embodiment, an insulator layer 24 is first formed on a substrate 22, and then N-type semiconductor layers 23 and P-type semiconductor layers 25 are repeatedly stacked on top of the insulator layer 24 in this order with the insulator layer 24 interposed therebetween, thereby forming a stack of three N-type semiconductor layers 23, three P-type semiconductor layers 25, and seven insulator layers 24.

Each N-type semiconductor layer 23 is connected to an N-side connecting portion 23a provided at the base end, and an N-side electrode 26 is formed on a part of the N-side connecting portion 23a. Each P-type semiconductor layer 25 is connected to a P-side connecting portion 25a provided at the base end, and a P-side electrode 27 is formed on a part of the P-side connecting portion 25a.
Each of the above layers is patterned using a metal mask. By forming the layers while shifting the position of the metal mask, multiple N-type semiconductor layers 23, P-type semiconductor layers 25, and insulator layers 24 are stacked.
Further, lead wires 26a and 27a are connected to the N-side electrode 26 and the P-side electrode 27, respectively.

In this way, in the heat flow switching element 21 of the second embodiment, N-type semiconductor layers 23 and P-type semiconductor layers 25 are stacked alternately with insulator layers 24 sandwiched between them. Therefore, when an external voltage is applied, the electric charge e generated in response to the increased number of interfaces increases, resulting in greater changes in thermal conductivity and faster thermal response.

The heat flow switching element 21 of the second embodiment also includes an upper high thermal conductivity portion 28 provided on the top surface, a lower high thermal conductivity portion (substrate 22) provided on the bottom surface, and a peripheral heat insulating portion 29 provided to cover the outer edges of the N-type semiconductor layer 23, insulator layer 24, and P-type semiconductor layer 25, and the peripheral heat insulating portion 29 is formed from the above-mentioned nitride insulator material, which has lower thermal conductivity than the upper high thermal conductivity portion 28 and the lower high thermal conductivity portion (substrate 22).

That is, the peripheral heat insulating portion 29 is a metal nitride represented by M-Si-N-Te (wherein M represents at least one of Ta and Hf, and Te is an optional element), and is a nanocrystal.
Like the peripheral heat insulating portion 29, the insulator layer 24 is also a metal nitride represented by M-Si-N-Te (wherein M represents at least one of Ta and Hf, and Te is an optional element), and is preferably a nanocrystal.
In addition, the upper high thermal conductivity portion 28 is formed from a high thermal conductivity material such as silicon-based resin (silicone), and the base material 22, which is the lower high thermal conductivity portion, is a high thermal conductivity substrate formed from alumina or the like.

The peripheral heat insulating portion 29 covers the periphery of the uppermost insulating layer 24 while leaving the uppermost insulating layer 24 exposed, and the upper high thermal conductivity portion 28 is formed on the upper portion so as to contact the exposed uppermost insulating layer 24.
The outer peripheral heat insulating portion 29 is also formed to cover the N-side electrode 26 and the P-side electrode 27 that are disposed on the outer periphery of each layer and connected to lead wires 26a and 27a.

In the second embodiment, the heat flow direction is the stacking direction (the direction of the arrow in FIG. 3 ), and for example, the upper high thermal conductivity section 28 side is the high temperature side, and the lower high thermal conductivity section, the substrate 22 side, is the low temperature side. As long as the heat flow direction is the stacking direction, the upper high thermal conductivity section 28 side may be the low temperature side, and the lower high thermal conductivity section, the substrate 22 side, may be the high temperature side.
As described above, in the heat flow switching element 21 of the second embodiment, the peripheral insulation portion 29 is formed of a nitride insulator material having lower thermal conductivity than the upper high thermal conductivity portion 28 on the top surface and the lower high thermal conductivity portion on the bottom surface of the substrate 22. Therefore, while the entire N-type semiconductor layer 23, insulator layer 24, and P-type semiconductor layer 25 serve as a heat flow path, heat can be prevented from flowing via the peripheral insulation portion 29, whose thermal conductivity does not change, and heat flow switching ability can be obtained in the stacking direction.

Next, the third embodiment differs from the second embodiment in that the second embodiment uses a heat flow switching element, whereas the third embodiment uses a thermoelectric conversion element 31 as shown in FIG.
That is, the thermoelectric conversion element 31 of the third embodiment comprises an insulating substrate 32, a P-type thin-film thermoelectric conversion portion 33p and an N-type thin-film thermoelectric conversion portion 33n formed on the insulating substrate 32, a connection electrode portion 34 connecting the P-type thin-film thermoelectric conversion portion 33p and the N-type thin-film thermoelectric conversion portion 33n, a pair of electrode terminal portions 35 formed at the ends of the connected P-type thin-film thermoelectric conversion portion 33p and N-type thin-film thermoelectric conversion portion 33n, and an insulator film 39 covering the surfaces of the insulating substrate 32, the P-type thin-film thermoelectric conversion portion 33p, the N-type thin-film thermoelectric conversion portion 33n, and the connection electrode portion 34.

The insulator film 39 is formed from the same nitride insulator material as in the first embodiment. That is, the insulator film 39 is a metal nitride nanocrystal film represented by the formula M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element).

At least one of the P-type thin-film thermoelectric conversion portion 33p and the N-type thin-film thermoelectric conversion portion 33n is formed of a nitride thermoelectric conversion material.
For example, the nitride thermoelectric conversion material is made of a metal nitride represented by the general formula: (Cr _1-x M _x ) _1-y N _y (where M represents at least one of Ti, V, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W, Si, Al, B, and Y; 0≦x<1.0, 0.40≦y<0.54), has a cubic NaCl-type crystal structure (space group Fm-3m (No. 225)), and has P-type or N-type thermoelectric properties.

In this embodiment, both the P-type thin-film thermoelectric conversion unit 33p and the N-type thin-film thermoelectric conversion unit 33n are formed from the above-mentioned nitride thermoelectric conversion material, but the P-type thin-film thermoelectric conversion unit may be formed from an organic thermoelectric material (printed material), and the N-type thin-film thermoelectric conversion unit 33n may be formed from the above-mentioned nitride thermoelectric conversion material.

The P-type thin-film thermoelectric conversion units 33p and N-type thin-film thermoelectric conversion units 33n are formed in multiple lines or strips, extending parallel to each other and arranged alternately. The ends of adjacent P-type thin-film thermoelectric conversion units 33p and N-type thin-film thermoelectric conversion units 33n are connected by connection electrode units 34, forming a single thin-film thermoelectric conversion unit that is folded back multiple times, with a pair of electrode terminal units 35 formed at both ends.

The connection electrode portion 34 and the electrode terminal portion 35 are patterned and made of Ag, Ag alloy, or the like.
Lead wires 36 are connected to the pair of electrode terminals 35 , and the lead wires 36 are connected to a power source 37 .

The insulating substrate 32 is preferably made of a material with low thermal conductivity, and can be, for example, an insulating film or glass. The insulating film can be, for example, a polyimide resin sheet. Other insulating films may also be used, such as LCP (liquid crystal polymer), PET (polyethylene terephthalate), or PEN (polyethylene naphthalate). The glass substrate can be, for example, alkali-free glass, alkali glass, or glass film.

When an insulating film is used for the insulating substrate 32, the resulting thermoelectric conversion element 31 is a sheet-type. For example, it can be a sheet-type Peltier element (cooling element) that converts electrical energy into thermal energy and transports heat, a sheet-type Seebeck element (thermoelectric power generation element) that converts thermal energy into electrical energy and generates electricity due to temperature differences, or a sheet-type thermopile that functions as an infrared sensor that applies the principles of a thermocouple.

In this way, in the thermoelectric conversion element 31 of the third embodiment, the insulator film 39 is formed from the above-mentioned nitride insulator material, and since the surface is covered with the insulator film 39 made of a nitride insulator material with low thermal conductivity, heat release from the surfaces of the P-type thin-film thermoelectric conversion section 33p and the N-type thin-film thermoelectric conversion section 33n is suppressed, and a sufficient temperature difference between the high-temperature side and the low-temperature side can be ensured.
Furthermore, when the P-type thin-film thermoelectric conversion unit 33p and the N-type thin-film thermoelectric conversion unit 33n are nitrides, the insulator film 39 is also a nitride, and therefore the bonding strength at the interfaces between the P-type thin-film thermoelectric conversion unit 33p and the N-type thin-film thermoelectric conversion unit 33n and the insulator film 39 is increased.

Next, the fourth embodiment differs from the third embodiment in that the P-type thin-film thermoelectric conversion portion 33p, the N-type thin-film thermoelectric conversion portion 33n, and the insulator film 39 are all film-like, whereas in the thermoelectric conversion elements 41A and 41B of the fourth embodiment, the P-type thermoelectric conversion portion 43p, the N-type thermoelectric conversion portion 43n, and the insulator 49 are all bulk rather than film-like, as shown in Figures 5(a) and 5(b).

Furthermore, in the third embodiment, the ends of adjacent P-type and N-type thin-film thermoelectric conversion units 33p and 33n are connected by connecting electrode units 34 on the same plane, forming a single thin-film thermoelectric conversion unit that is folded over multiple times as a whole, whereas in the fourth embodiment, the ends of adjacent bulk P-type and N-type thermoelectric conversion units 43p and 43n are connected by upper and lower connecting electrode units 44, forming a continuous thermoelectric conversion unit that is folded over multiple times as a whole in vertical cross section.

In this embodiment, a bulk insulator 49 made of the above-mentioned nitride insulator material is bonded to both sides of the P-type thermoelectric conversion unit 43p and the N-type thermoelectric conversion unit 43n, covering the side surfaces (surfaces).
The P-type thermoelectric conversion portion 43p, the N-type thermoelectric conversion portion 43n, the insulator 49, and the connection electrode portion 44 are sandwiched between insulating substrates 42A and 42B.

In the thermoelectric conversion element 41A shown in FIG. 5(a), the insulator 49 joined to the side surface of the P-type thermoelectric conversion unit 43p and the insulator 49 joined to the side surface of the N-type thermoelectric conversion unit 43n are in contact with each other. In contrast, in the thermoelectric conversion element 41B shown in FIG. 5(b), the insulator 49 joined to the side surface of the P-type thermoelectric conversion unit 43p and the insulator 49 joined to the side surface of the N-type thermoelectric conversion unit 43n are spaced apart and do not contact each other.

In this way, in the thermoelectric conversion elements 41 and 41B of the fourth embodiment, the insulator 49 is formed from the above-mentioned nitride insulator material. Therefore, because the surface (side surface) is covered with the insulator 49 made of a nitride insulator material with low thermal conductivity, heat release from the surface is suppressed even when the element is constructed in bulk, and a sufficient temperature difference between the high-temperature side and the low-temperature side can be ensured.

The crystal structure, thermal effusivity, and electrical resistivity of the examples of the present invention were measured in which the materials (Ta—Si—N, Hf—Si—N, Ta—Si—N—Te) listed in Tables 2 and 3 below were deposited on glass substrates by reactive sputtering in a nitrogen-containing atmosphere based on the first embodiment. The results of the crystal structure and thermal effusivity are shown in Tables 2 and 3.
The composition of each example was set by changing the nitrogen fraction (N ₂ /(Ar+N ₂ )) and the Si/(M+Si) ratio.
The composition was analyzed by elemental analysis using X-ray photoelectron spectroscopy (XPS). XPS quantitative analysis was performed on the sputtered surface at a depth of 20 nm from the outermost surface using Ar sputtering. The quantitative accuracy of N/(M + Si + N) was ±2%, and that of Si/(M + Si) was ±1%.

As comparative examples, the thermal effusivity and electrical resistivity of films made of Al—N, HfO ₂ , Ta—Si, Hf—Si, and Si—N were also measured. The results of the crystal structure and thermal effusivity are also shown in Table 1.
A magnetron sputtering device was used for sputtering, and a nitride insulating material film was formed to a thickness of 200 nm on a glass substrate (20×20×0.5 mm) by RF method, and Mo was sputtered to a thickness of 100 nm on the resulting film to form a device.
The surface roughness Ra of each of the nitride insulating material films after sputtering was small, less than 2 nm. The surface roughness Ra was evaluated using X-ray reflectivity measurement.

The thermal effusivity was measured by the FF method (surface heating/surface temperature measurement) of the pulsed light heating thermoreflectance method (using a thin film thermal property measuring device: PicoTherm PicoTR). The measurement was carried out at room temperature.
The thermal conductivity is calculated from the thermal effusivity using the following formula:
Thermal conductivity k = (thermal effusivity b) ² /volume heat capacity
= (thermal effusivity b) ² / (specific heat × density)

From these results, all of the examples of the present invention were low thermal conductive materials with a thermal effusivity of less than 2000 Ws ^0.5 /m ² K. Furthermore, all of the comparative examples had a thermal effusivity of 2000 Ws ^0.5 /m ² K or more, whereas among the examples of the present invention, Hf—Si—N, Ta—Si—N—Te, and Ta—Si—N containing 17.9 at% or more of Ta were particularly low thermal conductive materials with a thermal effusivity of less than 1700 Ws ^0.5 /m ² K.
In Ta-Si-N, increasing the amount of Ta tends to decrease the thermal effusivity and increase the volumetric heat capacity. When the Ta content is 17.9 at% or more, a material with low thermal conductivity of less than 1 Ws ^0.5 /m ² K and high thermal insulation properties can be obtained.
Furthermore, the thermal effusivity of Example 35 (Ta-Si-N-Te), which contained Te, was 250 Ws ^0.5 /m ² K. Example 35 had a thermal effusivity that was significantly smaller than Examples 1 to 34, and was a low thermal conductive material with a thermal effusivity of less than 1000 Ws ^0.5 /m ² K. Example 35 exhibits very low thermal conductivity, i.e., very high thermal insulation, and is therefore more suitable as an insulator layer that constitutes a heat flow switching element and an insulator layer that constitutes a thermoelectric conversion element.
The electrical resistivity of each example of the present invention was 10 ⁸ Ωcm or more, indicating high insulating properties. Comparative Examples 3 and 4 were metal compounds containing no nitrogen, and all had electrical resistivities of less than 10 Ωcm. Comparative Examples 1, 2, and 5 had electrical resistivities of 10 ⁸ Ωcm or more, indicating high insulating properties, but all were highly thermally conductive materials with thermal effusivities of 2000 Ws ^0.5 /m ² K or more.
The electrical resistivity of both the M-Si-N-Te of the example (where M represents at least one of Ta and Hf, and Te is an optional element) and the Si-N of comparative example 5 was 10 ⁸ Ωcm or more, but because the example contains the heavy metal element Ta or Hf, the lattice thermal conductivity is smaller than that of Si-N, resulting in a smaller thermal effusivity.
This electrical resistivity measurement (insulation evaluation test) was performed using the arrangement shown in FIG. 6 . The measurement was performed at room temperature. Specifically, a 100 mm M-Si-N-Te (where M represents at least one of Ta and Hf, and Te is an optional element) thin film 12, which is the nitride insulator material of the present invention, was formed on a Si substrate 11. A 50 nm Mo electrode 13 was then formed thereon. A voltage was applied between the Si substrate 11 and the Mo electrode 13 using a high-voltage source meter, and the electrical resistivity was determined based on the current value. The M-Si-N-Te thin film (100 mm) 12 had an area 100 times or more larger than that of the Mo electrode 13, and the Mo electrode 13 was positioned approximately at the center of the M-Si-N-Te thin film (100 mm) 12, thereby preventing surface current from flowing to the periphery of the M-Si-N-Te thin film 12 and enabling measurement of the electrical resistivity of the film itself.

As can be seen from Tables 2 and 3, the crystal structure of each of the examples of the present invention was nanocrystalline, whereas the Al—N comparative example 1 had columnar crystals. The thermal effusivity of the Al—N columnar crystals of comparative example 1 was significantly greater than 2000 Ws ^0.5 /m ² K.
_HfO2 Comparative Example 2, Ta-Si Comparative Example 3, Hf-Si Comparative Example 4, and Si-N Comparative Example 5 all had nanocrystalline crystal structures, but had thermal effusivities of 2000 Ws ^0.5 /m ² K or higher. In particular, Ta-Si Comparative Example 3 and Hf-Si Comparative Example 4 were metal compounds that did not contain nitrogen, and had high thermal effusivities of 2500 Ws ^0.5 /m ² K or higher.

Next, for Example 5 in Table 2, an XRD pattern (using a fully automatic multipurpose X-ray diffractometer (SmartLab: manufactured by RIGAKU)) is shown in FIG. 7, and a cross-sectional SEM image (45-degree oblique field of view, 200,000x magnification) is shown in FIG. 8. This cross-sectional SEM image was taken from a substrate that was cleaved. FIG. 8 shows both the cross-sectional structure and surface structure of the Ta-Si-N film. It can be seen that Example 5 of the present invention has high surface smoothness, is dense, and has high density.
Thin-film XRD was performed using grazing incidence X-ray diffraction (thin-film XRD) under conditions of a Cu tube and an incident angle of 1 degree. No sharp peaks indicating long-period crystallinity, which would suggest a relatively large crystal size, were detected.

Furthermore, Fig. 9 shows cross-sectional SEM images (45-degree oblique field of view, 50,000x magnification) of Examples 7 and 25 of the present invention. This cross-sectional SEM image was taken from a substrate that had been cleaved. Fig. 9 also shows the cross-sectional and surface structures of the Ta-Si-N film and the Hf-Si-N film. It can be seen that Examples 7 and 25 of the present invention have high surface smoothness, are dense, and have high density.
Furthermore, Fig. 10 shows cross-sectional TEM (HAADF-STEM) images (high-angle annular dark-field scanning transmission electron microscope) of Examples 7 and 25. The magnification of this TEM image is 1,050,000 times.
As can be seen from these images, the crystalline structures of Examples 7 and 25 of the present invention are dense nanocrystals with a crystal size of 5 nm or less. Note that in this specification, the term "nanocrystal" refers to any material with a crystal size of 5 nm or less, including amorphous materials.

Next, a detailed analysis of the cross-sectional structure of Ta—Si—N and Hf—Si—N was performed using a TEM device. Electron beam diffraction images of the film cross sections of Examples 7 and 25 are shown in FIG. 11. In neither case were electron beam diffraction images showing long-period crystallinity, which would suggest a relatively large crystal size, detected, indicating that the crystal size was very small or that the nanocrystals were amorphous. The TEM image observation results show that the Examples are dense nanocrystals with crystal sizes of 5 nm or less. Furthermore, these images show that the diffraction rings are clearer in Example 25 than in Example 7, indicating that nanocrystals with smaller crystal sizes were obtained in Example 7 (Ta—Si—N) than in Example 25 (Hf—Si—N).
Grazing incidence X-ray diffraction (thin film XRD) was also performed, and peaks indicating a crystallized film were observed for the columnar crystal material of the comparative example, but no sharp peaks indicating long-period crystallinity, which would suggest a relatively large crystal size, were detected for the example. The results of XRD, SEM, and TEM show that the example is made of very small or amorphous nanocrystals with a crystal size of 5 nm or less.

Furthermore, it can be seen that the nanocrystal films of the examples have high surface smoothness (surface roughness Ra of less than 2 nm), and are dense and high density.
In other words, the low thermal conductivity (high thermal insulation) is not due to low density, such as voids, but rather indicates that the nitride material itself has low thermal conductivity. These results show that nanocrystalline crystal size reduces thermal conduction due to vibrations (phonons, lattice vibrations) transmitted between crystal lattices, reducing lattice thermal conduction and resulting in a low thermal conductivity semiconductor material with a thermal effusivity of less than 2000 Ws ^0.5 /m ² K. Furthermore, among the examples of the present invention, Hf-Si-N, Ta-Si-N-Te, and Ta-Si-N containing 17.9 at% or more of Ta in particular exhibited low thermal conductivity with a thermal effusivity of less than 1700 Ws ^0.5 /m ² K.
Furthermore, the thermal effusivity of Example 35 (Ta-Si-N-Te), which contains Te, was 250 Ws ^0.5 /m ² K, making it a very low thermal conductive material with a thermal effusivity of less than 1000 Ws ^0.5 /m ² K. XRD, SEM, and TEM of Example 35 were performed, confirming that it was a nanocrystalline film with a crystal size of 5 nm or less. Furthermore, it was found that Example 35 had high surface smoothness (surface roughness Ra less than 2 nm), and was dense and high-density. In other words, even in Example 35 (Ta-Si-N-Te), which contains Te, the low thermal conductivity (high thermal insulation) is not due to low density such as voids, but rather indicates that the nitride material containing Te itself has low thermal conductivity. Because it exhibits very low thermal conductivity, i.e., very high thermal insulation, it is more suitable as an insulator layer constituting a heat flow switching element and as an insulator layer constituting a thermoelectric conversion element.
The composition ranges of each element in M-Si-N-Te in Examples 1 to 35 were 5.9 to 37.9 at% for M, 8.0 to 44.1 at% for Si, 42.6 to 59.0 at% for N, and 0 to 8.4 at% for Te, with the total of each element being 100 at%. Also, Si/(M+Si) was 17.4 to 87.2 at%.

The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

1, 21...heat flow switching element, 3, 23...N-type semiconductor layer, 4, 24...insulator layer, 5, 25...P-type semiconductor layer, 22...substrate (lower high thermal conductivity portion), 28...upper high thermal conductivity portion, 29...periphery heat insulating portion, 31, 41A, 41B...thermoelectric conversion element, 32...insulating substrate, 33p...P-type thin-film thermoelectric conversion portion, 43p...P-type thermoelectric conversion portion, 33n...N-type thin-film thermoelectric conversion portion, 43n...N-type thermoelectric conversion portion, 34, 44...connection electrode portion, 39...insulator film, 49...insulator

Claims (10)

A nitride insulating material is a metal nitride represented by M-Si-N-Te (where M represents at least one of Ta and Hf), and is characterized by being a nanocrystal. The nitride insulating material according to claim 1 ,
A nitride insulating material characterized by a thermal effusivity of less than 2000 Ws ^0.5 /m ² K. The nitride insulating material according to claim 2,
A nitride insulating material characterized by a thermal effusivity of less than 1700 Ws ^0.5 /m ² K. The nitride insulating material according to any one of claims 1 to 3,
A nitride insulating material characterized by having an electrical resistivity of 10 ⁸ Ωcm or more. The nitride insulating material according to any one of claims 1 to 4,
A nitride insulating material characterized by being used as a low thermal conductive material. an N-type semiconductor layer;
an insulator layer stacked on the N-type semiconductor layer;
a P-type semiconductor layer stacked on the insulator layer,
A thermal flow switching element, wherein the insulating layer is formed from the nitride insulating material according to claim 1 . 7. The thermal flow switching element according to claim 6,
an upper high thermal conductivity portion provided on the top surface;
a lower high thermal conductivity portion provided on the bottom surface;
a peripheral heat insulating portion provided to cover peripheral edges of the N-type semiconductor layer, the insulator layer, and the P-type semiconductor layer,
A heat flow switching element, wherein the outer peripheral heat insulating portion is formed of the nitride insulating material having lower thermal conductivity than the upper high thermal conductivity portion and the lower high thermal conductivity portion. an insulating substrate;
a P-type thermoelectric conversion section and an N-type thermoelectric conversion section formed on the insulating substrate;
a connection electrode portion that connects the P-type thermoelectric conversion portion and the N-type thermoelectric conversion portion;
an insulator covering surfaces of the P-type thermoelectric conversion unit and the N-type thermoelectric conversion unit;
A thermoelectric conversion element, characterized in that the insulator is formed from the nitride insulator material according to any one of claims 1 to 5. The thermoelectric conversion element according to claim 8,
The thermoelectric conversion element is characterized in that the P-type thermoelectric conversion portion, the N-type thermoelectric conversion portion, and the insulator are in the form of a film. A method for producing the nitride insulating material according to any one of claims 1 to 5, comprising the steps of:
A method for producing a nitride insulating material, characterized by forming a film by reactive sputtering in a nitrogen-containing atmosphere using an M-Si-Te sputtering target (where M represents at least one of Ta and Hf).