Heat flow switching element

Abstract

To provide a heat flow switching element having a larger change in thermal conductivity and excellent thermal responsiveness.SOLUTION: A heat flow switching element includes semiconductor layers 2N and 2P, and an insulator layer 3 laminated on the semiconductor layers, the insulator layer contains an ionic liquid. In particular, it is preferable that the insulator layer is a porous body containing the ionic liquid. The heat flow switching element may also include a P-type semiconductor layer 2P, the insulator layer 3 laminated on the P-type semiconductor layer, and an N-type semiconductor layer 2N laminated on the insulator layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heat flow switching element whose thermal conductivity can be actively controlled by a bias voltage. [Background technology]

[0002] Conventionally, as a thermal switch that changes thermal conductivity, for example, Patent Document 1 describes a thermal diode in which two thermal conductors with different thermal expansion coefficients are lightly brought into contact with each other, and the way heat flows varies depending on the direction of the temperature gradient. Patent Document 2 also describes a heat dissipation device that is a thermal switch that uses physical thermal contact due to thermal expansion.

[0003] Furthermore, Patent Document 3 describes a variable thermal conductivity device in which the thermal conductivity changes due to a reversible oxidation-reduction reaction that occurs when a voltage is applied to a compound. Furthermore, Non-Patent Document 1 describes a method for bonding a polyimide tape to two Ag2S 0.6 Se 0.4 A heat flow switching element has been proposed in which thermal conductivity is changed by applying an electric field to a material sandwiched between two electrodes.

[0004] The technologies described in Patent Documents 1 and 2 above use physical thermal contact due to thermal expansion, so reproducibility is not possible, and size design is difficult due to minute changes, and plastic deformation due to mechanical contact pressure cannot be avoided. In addition, there is a problem that the influence of convection heat transfer between materials is too large. Furthermore, the technology described in Patent Document 3 uses a redox reaction, which is a chemical reaction, and has the disadvantages of being poor in thermal responsiveness and unstable in thermal conductivity. In contrast to these, the technology described in Non-Patent Document 1 generates charges that can change the thermal conductivity at the material interface by applying a voltage, and heat can be transported by the charges, so that a state in which the thermal conductivity has changed can be immediately transitioned to, and relatively good thermal responsiveness can be obtained. However, since the amount of charge generated is small, a heat flow switching element that generates a larger amount of charge and changes the thermal conductivity even more has been desired (Note that, as described above, a "heat flow switching element" is an element whose thermal conductivity changes depending on a bias voltage, and is an element that has a different function from so-called thermoelectric modules and thermoelectric elements that convert heat into electric power).

[0005] Therefore, the present applicants have developed a heat flow switching element including an N-type semiconductor layer, an insulator layer laminated on the N-type semiconductor layer, and a P-type semiconductor layer laminated on the insulator layer (see Patent Document 4). In this heat flow switching element, when an external voltage is applied to the N-type semiconductor layer and the P-type semiconductor layer, 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 charges carry heat, causing a change in thermal conductivity, resulting in a large change in thermal conductivity and high thermal responsiveness. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 2781892 [Patent Document 2] Patent No. 5402346 [Patent Document 3] JP 2016-216688 A [Patent Document 4] Patent Publication No. 2021-125578 [Non-patent literature]

[0007] [Non-Patent Document 1] Takuya Matsunaga and 4 others, "Fabrication of a heat flow switching element operated by bias voltage," 15th Annual Meeting of the Thermoelectric Society of Japan, September 13, 2018 Summary of the Invention [Problem to be solved by the invention]

[0008] The above conventional techniques still have the following problems. That is, in the technology described in Patent Document 4, 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 the thermal conductivity changes as the electric charges carry heat, but the generated electric charges are limited only near the interfaces, and the total amount is small. In addition, the amount of electric charge is determined by the mobility of electrons in the material, so the mobility is limited between solid semiconductors and insulators. For this reason, there is a demand for a heat flow switching element that induces more electric charges to increase the amount of electric charges and thus causes a larger change in thermal conductivity.

[0009] The present invention has been made in view of the above-mentioned problems, and has an object to provide a heat flow switching element having a larger change in thermal conductivity and excellent thermal responsiveness. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention employs the following configuration: A heat flow switching element according to a first aspect of the invention includes a semiconductor layer and an insulator layer laminated on the semiconductor layer, and the insulator layer contains an ionic liquid.

[0011] In this heat flow switching element, since the insulator layer contains an ionic liquid, even if the external voltage applied to the insulator layer and the semiconductor layer is as small as a few volts, ions are induced in the ionic liquid, which is an ion conductor, near the semiconductor layer of the insulator layer, and charges are induced near the insulator layer of the semiconductor layer by the ions. Therefore, the electronic thermal conductivity of the semiconductor layer is increased by the induced charges. That is, an electric double layer is formed by the ions induced in the insulator layer, and the amount of charge induced on the semiconductor layer side is greater than the polarization of the insulator layer of the dielectric that does not contain the ionic liquid. In addition, the mobility of ions in the ionic liquid is overwhelmingly greater than the mobility of charges in the dielectric, so that the heat flow switching property is superior to that of the conventional one.

[0012] The heat flow switching element according to the second invention is characterized in that, in the first invention, it comprises a P-type semiconductor layer, an insulator layer stacked on the P-type semiconductor layer, and an N-type semiconductor layer stacked on the insulator layer. That is, this heat flow switching element includes a P-type semiconductor layer, an insulator layer laminated on the P-type semiconductor layer, and an N-type semiconductor layer laminated on the insulator layer. When an external voltage is applied to the N-type semiconductor layer and the P-type semiconductor layer, cations are induced in the ionic liquid, which is an ion conductor, near the N-type semiconductor layer of the insulator layer, and negative charges (electrons) are induced near the insulator layer of the N-type semiconductor layer by the cations. In addition, anions are induced in the ionic liquid near the P-type semiconductor layer of the insulator layer, and positive charges (holes) are induced near the insulator layer of the P-type semiconductor layer by the anions. Therefore, the electronic thermal conductivity of the N-type semiconductor layer and the P-type semiconductor layer is increased by the induced charges. That is, an electric double layer is formed by the cations near the N-type semiconductor layer and the anions near the P-type semiconductor layer induced in the insulator layer, and the amount of charge induced on the two semiconductor layer side is greater than the polarization of the insulator layer of a dielectric that does not contain ionic liquid.

[0013] The heat flow switching element according to a third invention is the heat flow switching element according to the second invention, characterized in that it comprises an N-side electrode connected to the N-type semiconductor layer and made of a metal, and a P-side electrode connected to the P-type semiconductor layer and made of a metal.

[0014] A fourth aspect of the present invention is a heat flow switching element according to any one of the first to third aspects, characterized in that the insulator layer is a porous body containing an ionic liquid. That is, in this heat flow switching element, the insulator layer is a porous material containing ionic liquid, so that a large amount of ionic liquid can be impregnated and retained within the insulator layer, and the ions in the ionic liquid can move more easily within the insulator layer.

[0015] The heat flow switching element of the fifth invention is characterized in that, in any one of the first to fourth inventions, the semiconductor layer and the insulator layer are laminated directly or via another layer on a substrate of a flexible insulating film, and the semiconductor layer and the insulator layer are flexible and entirely sheet-like. That is, in this heat flow switching element, a semiconductor layer and an insulator layer are laminated directly or through other layers on a substrate of flexible insulating film, and since the semiconductor layer and the insulator layer are flexible and the entire element is in sheet form, it is possible to attach the element to the curved surface of the object to be measured as a flexible element, or to wrap the element in multiple layers to form a roll structure.

[0016] A sixth aspect of the present invention is the heat flow switching element of any one of the first to fifth aspects, characterized in that the insulating layer is paraffin paper containing the ionic liquid. That is, in this heat flow switching element, the insulating layer is made of paraffin paper containing ionic liquid, so that the gaps between the fibers of the paraffin paper can be saturated with a large amount of ionic liquid.

[0017] A seventh aspect of the present invention is a heat flow switching element according to any one of the first to sixth aspects of the present invention, The ionic liquid is CH 20It is characterized by being NOBF4.

[0018] A heat flow switching element according to an eighth aspect of the present invention is any one of the first to sixth aspects of the present invention, The ionic liquid is CH 11 It is characterized by being F6N3O4S2.

[0019] The heat flow switching element according to a ninth aspect of the present invention is the heat flow switching element according to any one of the first to eighth aspects of the present invention, characterized in that the semiconductor layers and the insulator layers are alternately stacked in multiple layers. In other words, in this heat flow switching element, semiconductor layers and insulator layers are stacked alternately in multiple layers, and the amount of ions and charges generated increases in accordance with the increased number of stacked insulator layers, resulting in greater changes in thermal conductivity and higher thermal responsiveness. Effect of the Invention

[0020] According to the present invention, the following effects are obtained. That is, in the heat flow switching element according to the present invention, since the insulator layer contains an ionic liquid, even with a small external voltage of a few volts, an electric double layer is formed by ions induced in the insulator layer, and the amount of charge induced on the semiconductor layer side becomes larger than in the past. Also, since the mobility of ions is overwhelmingly larger than the mobility of charges in the dielectric, it is possible to obtain a larger change in thermal conductivity and excellent heat flow switching properties than in the past. [Brief description of the drawings]

[0021] [Figure 1] 1 is a conceptual cross-sectional view showing a first embodiment of a heat flow switching element according to the present invention. [Diagram 2] FIG. 2 is a conceptual diagram for explaining the principle in the first embodiment. [Diagram 3] FIG. 2 is a conceptual cross-sectional view showing another example (heat flow switching element 1A) of the first embodiment of the heat flow switching element according to the present invention. [Figure 4]FIG. 2 is a conceptual cross-sectional view showing another example (heat flow switching element 1B) of the first embodiment of the heat flow switching element according to the present invention. [Diagram 5] FIG. 2 is a conceptual cross-sectional view showing another example (heat flow switching element 1C) of the first embodiment of the heat flow switching element according to the present invention. [Figure 6] FIG. 2 is a perspective view showing a case in which a heat flow switching element is wound around a measurement object in the first embodiment. [Figure 7] FIG. 4 is a conceptual cross-sectional view showing a second embodiment of a heat flow switching element according to the present invention. [Figure 8] FIG. 11 is a conceptual plan view showing a heat flow switching element in the second embodiment. [Figure 9] FIG. 11 is a perspective view showing a case where the heat flow switching element is in a roll shape in the second embodiment. [Figure 10] FIG. 11 is a conceptual cross-sectional view showing a third embodiment of a heat flow switching element according to the present invention. [Figure 11] FIG. 11 is a perspective view for explaining a method for measuring the in-plane thermal conductivity in an embodiment of a heat flow switching element according to the present invention. [Figure 12] 4 is a graph showing the bias voltage dependence of thermal conductivity in Example 1 of the heat flow switching element according to the present invention. [Figure 13] 1 is a graph showing the results of an X-ray diffraction experiment of Ag2+ΔSxSe1-x with different composition ratios in an example according to the present invention. [Figure 14] 1 is a graph showing the results of an X-ray diffraction experiment of Ag2+ΔSxSe1-x with different composition ratios in an example according to the present invention. [Figure 15] 1 shows data on changes in thermal conductivity measured by a cyclic heating method for Example 1 and Example 2 in the examples according to the present invention. [Figure 16] 13 is a graph showing the bias voltage dependence of thermal conductivity in a heat flow switching element according to Example 3 of the present invention. [Figure 17]13 shows data on the change in thermal conductivity measured by a cyclic heating method for Example 3 in the embodiment according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A first embodiment of a heat flow switching element according to the present invention will be described below with reference to Figures 1 to 6. In the drawings used in the following description, the scale is appropriately changed as necessary to make each part recognizable or easily recognizable.

[0023] As shown in Figures 1 and 2, the heat flow switching element 1 of this embodiment includes semiconductor layers 2N and 2P and an insulator layer 3 laminated on the semiconductor layers 2N and 2P, and the insulator layer 3 contains an ionic liquid. Moreover, the heat flow switching element 1 of this embodiment includes a P-type semiconductor layer 2P, which is the semiconductor layer, the insulator layer 3 stacked on the P-type semiconductor layer 2P, and an N-type semiconductor layer 2N, which is the semiconductor layer stacked on the insulator layer 3. Furthermore, the heat flow switching element 1 of this embodiment includes an N-side electrode 4N connected to the N-type semiconductor layer 2N and made of metal, and a P-side electrode 4P connected to the P-type semiconductor layer 2P and made of metal.

[0024] The insulating layer 3 is paraffin paper (so-called medicine wrapping paper) containing an ionic liquid. Furthermore, the insulating layer 3 may be made of a porous material containing an ionic liquid. As the porous body, a separator made of porous polyethylene, polypropylene, polyolefin, cellulose, polyimide, aramid, nylon, polyvinylidene fluoride-hexafluoropropylene, or the like can be used. The porous material of the insulator layer 3 is preferably one that has low thermal conductivity of less than 0.3 W / mK and is highly insulating.

[0025] The ionic liquid is, for example, CH 20NOBF4 (also known as N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate) and CH 11 F6N3O4S2 (also known as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM] [TFSI]), etc. The anion species of the ionic liquid material is CH of the BF4 system (tetrafluoroborate system). 20 Compared to NOBF4, the above imide-based [(CF3SO2)2N] - (Bis(trifluoromethanesulfonyl)imide, TFSI, TFSA) C8H 11 When F6N3O4S2 or the like is used as the ionic liquid, the withstand voltage is improved. The ionic liquid is preferably a liquid at 25°C. In addition to the above, examples of the ionic liquid include CH3C3H3N2C4H9[(CF3SO2)2N], CH3C3H3N2C4H9PF6, CH3(CH3CH2CH2)C5H 10 N[(CF3SO2)2N],C8H 11 F6N3O4S2,C 10 H 20 F6N2O5S2, etc. These are known as organic nitrogen (ammonium) based ionic liquids.

[0026] The melting points of the ionic liquids listed above are CH 20 NOBF4 is 9℃, CH3C3H3N2C4H9[(CF3SO2)2N] is -4℃, CH3C3H3N2C4H9PF6 is 6.5℃, CH3(CH3CH2CH2)C5H 10 N[(CF3SO2)2N] is 12℃, C8H 11 F6N3O4S2 is -3℃,C 10 H 20 F6N2O5S2 has a melting point of -15°C and is liquid at 25°C. The insulating layer 3 may be made of a gelled ionic liquid.

[0027] The semiconductor layers 2N and 2P are, for example, Ag 2+δ S x Se1-x In this case, the P-type and N-type of the semiconductor layers 2N and 2P are determined by the x value and the addition of N-type and P-type dopants. For example, Ag2S 0.6 Se 0.4 becomes the N-type semiconductor layer 2N. In this way, the semiconductor layers 2N and 2P are represented by the chemical formula A 2+δ M (where A is at least one of Ag and Cu, and M is at least one of S, Se and Te. δ is in the range of -0.5≦δ≦+0.5) can be particularly used. For example, the above Ag 2+δ S x Se 1-x In addition, Ag5Te3 (δ=-1 / 3) or the like can be used for the semiconductor layers 2N and 2P.

[0028] The semiconductor layers 2N and 2P preferably have a low thermal conductivity of less than 2 W / mK, and more preferably have a low thermal conductivity of less than 1 W / mK. Moreover, the semiconductor layers 2N and 2P preferably have a low electrical resistance of 10 Ωm or less, and, with regard to thermal conductivity, have a high electronic thermal conductivity. Various deposition methods are used to form each layer, including sputtering, molecular beam deposition (MBD), atomic layer deposition (ALD), chemical vapor deposition (CVD), chemical solution deposition (CSD), sol-gel, etc. Note that molecular beam epitaxy (MBE), known as one of the methods used for crystal growth of semiconductors, etc., is included in the molecular beam deposition (MBD) technology. The N-side electrode 4N and the P-side electrode 4P are formed of a metal such as Mo, Al, or Cu. An external power source V is connected to the N-side electrode 4N and the P-side electrode 4P, and a voltage is applied thereto.

[0029] As another example of the first embodiment (thermal flow switching element 1A), in the above embodiment, the insulator layer 3 is sandwiched and laminated between the N-type semiconductor layer 2N and the P-type semiconductor layer 2P, but as shown in FIG. 3, it is also acceptable to laminate two layers, that is, the insulator layer 3 and one of the N-type semiconductor layer 2N or the P-type semiconductor layer 2P, the semiconductor layer 2N, 2P. Furthermore, if a voltage can be applied directly to the N-type semiconductor layer 2N and the P-type semiconductor layer 2P, the N-side electrode 4N and the P-side electrode 4P are not necessary.

[0030] In another example (heat flow switching element 1A) of the first embodiment, a voltage can be applied directly to the N-type semiconductor layer 2N without using the N-side electrode 4N, and the N-type semiconductor layer 2N also functions as an electrode. That is, wire bonding or lead wires may be directly connected to the N-type semiconductor layer 2N. In particular, the above Ag 2+δ S x Se 1-x The N-type semiconductor layer 2N can be used as an electrode having low thermal conductivity.

[0031] In the above heat flow switching element 1A, the N-side electrode 4N is omitted and the N-type semiconductor layer 2N serves as the N-side electrode. However, as in FIG. 1, as another example (heat flow switching element 1B), the N-side electrode 4N may be formed on the N-type semiconductor layer 2N as shown in FIG. 4. In this manner, in the heat flow switching element 1B, electrodes (N-side electrode 4N, P-side electrode 4P) are formed above and below the two-layer structure of the insulating layer 3 and the N-type semiconductor layer 2N.

[0032] Furthermore, as another example (heat flow switching element 1C) of the first embodiment, each layer may be laminated on a substrate 5 as shown in Fig. 5. For example, a P-side electrode 4P, an insulator layer 3, an N-type semiconductor layer 2N, and an N-side electrode 4N may be laminated in this order on an insulating substrate 5 such as a glass substrate. The material used for the insulating substrate 5 is preferably an insulating material having a low thermal conductivity of less than 2 W / mK, more preferably less than 1 W / mK. Therefore, even in the case of a glass substrate, a substrate material having a lower thermal conductivity is preferred. In this case, since each layer is laminated on the substrate 5, each layer is supported by the substrate 5, facilitating film formation and allowing the element to have stable strength and the like. The layers may be stacked in the reverse order on the substrate 5. The substrate 5 itself may serve as the P-side electrode 4P or the N-side electrode 4N.

[0033] In this embodiment, for example, in the layer structure shown in FIG. 1, the semiconductor layers 2N and 2P are made of a flexible material (e.g., Ag 2+δ S x Se 1-x When the heat flow switching element 1 is formed from a material such as a conductor, both ends can be connected to form a cylindrical shape, and the heat flow switching element 1 can be attached in a wound state to the outer circumferential surface of a cylindrical attachment object M, for example, as shown in FIG. 6. The cylindrical attachment object M is, for example, a pipe through which a heat medium flows.

[0034] In this way, since the heat flow switching element 1 is curved into a cylindrical shape, it can be installed so as to cover the outer circumferential surface of a cylindrical or columnar attachment object M, thereby making it possible to adjust the amount of heat released from a pipe or the like through which a heat medium flows. Also, by attaching this heat flow switching element 1 so as to cover the outer circumferential surface of a cylindrical container, it is possible to turn the cylindrical container into a heat storage container capable of adjusting temperature.

[0035] In this way, in the heat flow switching element 1 of the present embodiment, since the insulator layer 3 contains an ionic liquid, even if the external voltage applied to the insulator layer 3 and the semiconductor layers 2N, 2P is small, such as a few volts, as shown in FIG. 2, ions are induced in the ionic liquid, which is an ion conductor, near the semiconductor layers 2N, 2P of the insulator layer 3, and charges are induced near the insulator layer 3 of the semiconductor layers 2N, 2P by these ions. Therefore, the electronic thermal conductivity of the semiconductor layers 2N, 2P is increased by the induced charges. That is, an electric double layer is formed by the ions induced in the insulator layer 3, and the amount of charge induced on the semiconductor layers 2N, 2P side is greater than the polarization of the insulator layer of a dielectric that does not contain an ionic liquid. In addition, the mobility of ions in the ionic liquid is overwhelmingly greater than the mobility of charges in the dielectric, so that the heat flow switching property is superior to that of the conventional device.

[0036] In particular, by providing a P-type semiconductor layer 2P, an insulator layer 3 laminated on the P-type semiconductor layer 2P, and an N-type semiconductor layer 2N laminated on the insulator layer 3, when an external voltage is applied to the N-type semiconductor layer 2N and the P-type semiconductor layer 2P, positive ions (ion+) are induced in the ionic liquid, which is an ion conductor, near the N-type semiconductor layer 2N of the insulator layer 3, and negative charges (electrons) (e-) are induced near the insulator layer 3 of the N-type semiconductor layer 2N by these positive ions. In addition, negative ions (ion-) are induced in the ionic liquid near the P-type semiconductor layer 2P of the insulator layer 3, and positive charges (holes) (h+) are induced near the insulator layer 3 of the P-type semiconductor layer 2P by these negative ions.

[0037] For this reason, the electronic thermal conductivity of the N-type semiconductor layer 2N and the P-type semiconductor layer 2P increases due to the induced charges. That is, an electric double layer is formed by the cations near the N-type semiconductor layer 2N and the anions near the P-type semiconductor layer 2P induced in the insulator layer 3, and the amount of charge induced on the two semiconductor layers 2N and 2P side becomes larger than the amount of charge induced by the polarization of the insulator layer 3 of a dielectric that does not contain ionic liquid. Furthermore, when the insulator layer 3 is a porous body containing an ionic liquid, a large amount of the ionic liquid can be impregnated and retained within the insulator layer 3, and ions in the ionic liquid can move more easily within the insulator layer 3. Furthermore, when the insulating layer 3 is paraffin paper containing an ionic liquid, the gaps between the fibers of the paraffin paper can be impregnated with a large amount of ionic liquid. Paraffin is used as a component of medicine packaging paper, and paraffin paper, which is paper containing paraffin, is characterized by being chemically stable, insoluble in many liquids, and resistant to oxidation and atmospheric water when used in normal air. Therefore, paraffin paper containing ionic liquid is more chemically stable than normal paper containing ionic liquid, making it possible to use heat flow switching elements for a long period of time.

[0038] In addition, in Fig. 2, the type of charge (e-) generated in the vicinity of the insulator layer 3 of the N-type semiconductor layer 2N is an electron, which is represented by a black circle. Also, the type of charge (h+) generated in the vicinity of the insulator layer 3 of the P-type semiconductor layer 2P is a hole, which is represented by a white circle. (A hole is a hole created by a shortage of electrons in the valence band of a semiconductor, and appears to have a relatively positive charge.)

[0039] Next, second and third embodiments of the heat flow switching element according to the present invention will be described below with reference to Figures 7 to 10. In the following description of each embodiment, the same components as those described in the above embodiments are denoted by the same reference numerals, and the description thereof will be omitted.

[0040] The difference between the second embodiment and the first embodiment is that the heat flow switching element 1C of the first embodiment employs a substrate 5 which is a glass substrate, whereas the heat flow switching element 21 of the second embodiment employs a substrate 25 which is a flexible insulating film, as shown in Figures 7 to 9. That is, in the second embodiment, as shown in FIG. 7, semiconductor layers 2N and 2P and an insulator layer 3 are laminated on a substrate 25 made of an insulating film directly or via another layer.

[0041] In the second embodiment, the semiconductor layers 2N and 2P and the insulating layer 3 are flexible and are entirely in a sheet shape. For example, the semiconductor layers 2N and 2P may be made of flexible Ag 2+δ S x Se 1-x etc. can be adopted. As shown in FIG. 8, the insulating film substrate 25 is formed to extend in a strip shape longer than the laminated portion 26 of the semiconductor layers 2N and 2P and the insulating layer 3.

[0042] The insulating film substrate 25 is preferably made of an insulating material having a low thermal conductivity of less than 2 W / mK. More preferably, the insulating material has a low thermal conductivity of less than 1 W / mK. The insulating film substrate 25 is formed of a resin, and examples of the resin that can be used include a polyimide resin sheet. Other materials that can be used for the insulating film substrate 25 include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), and LCP (liquid crystal polymer).

[0043] In the heat flow switching element 21 of the second embodiment, as shown in FIG. 9, a substrate 25 of a strip-shaped insulating film on which a laminated portion 26 (an N-type semiconductor layer 2N, an insulator layer 3, and a P-type semiconductor layer 2P) is laminated is wound in a spiral shape as shown in FIG. That is, in the second embodiment, by spirally winding a strip-shaped insulating film substrate 25 into a cylindrical shape, laminated portion 26 on insulating film substrate 25 is spirally wound while sandwiching substrate 25.

[0044] The N-side electrode 4N and the P-side electrode 4P are provided near the central axis of the wound coil and are connected to an external wiring L. When this heat flow switching element 21 is rolled into a cylindrical shape, it becomes possible to control the heat flow in the axial direction. Thus, in the heat flow switching element 21 of the second embodiment, the semiconductor layers 2N, 2P and the insulator layer 3 are laminated directly or through other layers on a substrate 25 made of a flexible insulating film, and since the semiconductor layers 2N, 2P and the insulator layer 3 are flexible and in the form of a sheet as a whole, they can be wound in multiple layers to form a roll structure.

[0045] Next, the third embodiment differs from the first embodiment in that, in the heat flow switching element 1 of the first embodiment, one N-type semiconductor layer 2N, one insulator layer 3 and one P-type semiconductor layer 2P are stacked, whereas, in the heat flow switching element 31 of the third embodiment, multiple N-type semiconductor layers 2N and multiple P-type semiconductor layers 2P are stacked alternately with an insulator layer 3 sandwiched between them, as shown in FIG. 10. That is, in the third embodiment, an insulator layer 3 is first formed, and then an N-type semiconductor layer 2N and a P-type semiconductor layer 2P are repeatedly stacked on top of the insulator layer 3 in this order with the insulator layer 3 interposed therebetween to form a laminate of two N-type semiconductor layers 2N, two P-type semiconductor layers 2P, and five insulator layers 24.

[0046] Each N-type semiconductor layer 2N is connected to an N-side electrode 4N, which is an N-side connector provided at the base end. Also, each P-type semiconductor layer 2P is connected to a P-side electrode 4P, which is a P-side connector provided at the base end. That is, the tip portion of each N-type semiconductor layer 2N is disposed away from the P-side electrode 4P, and the insulating layer 3 is interposed between the tip portion and the P-side electrode 4P. Further, the tip portion of each P-type semiconductor layer 2P is disposed so as to be spaced apart from the N-side electrode 4N, and an insulating layer 3 is interposed between the tip portion and the N-side electrode 4N.

[0047] The semiconductor layers 2N and 2P are patterned using, for example, a metal mask. By forming the layers with the metal mask shifted in position, a plurality of N-type semiconductor layers 2N and a plurality of P-type semiconductor layers 2P are laminated. The insulating layer 3 is, for example, paraffin paper (so-called medicine wrapping paper) containing an ionic liquid, as in the first embodiment.

[0048] In this way, in the heat flow switching element 31 of the third embodiment, the N-type semiconductor layers 2N and the P-type semiconductor layers 2P are stacked alternately with the insulator layer 3 in between, so that when an external voltage is applied, the charge generated in response to the increased number of ions due to stacking also increases, resulting in a greater change in thermal conductivity and high thermal responsiveness. EXAMPLES

[0049] In order to measure the in-plane heat flow in the heat flow switching element of the present invention, as shown in FIG. 11, a heat flow switching element 1C, which is another example of the first embodiment, was used as a sample and its thermal conductivity was measured using a cyclic heating method.

[0050] The element of Example 1 of the present invention was fabricated as follows. A Mo electrode was formed to a thickness of 100 nm by sputtering on the glass substrate 5. This Mo electrode was designated as a P-side electrode 4P. In addition, Ag was deposited on a 25 μm thick medicine wrapping paper (paraffin paper) by molecular beam deposition (MBD). 2+δ S 0.75 Se 0.25 The Ag film was deposited at 910 nm. 2+δ S x Se 1-x is defined as an N-type semiconductor layer. Next, add about 10 mL of C8H 20 NOBF4 (ionic liquid) is soaked into the paper to form a porous body (paper wrap) containing ionic liquid. This porous body containing ionic liquid is electrically insulated and is used as an insulating layer. Next, this medicine wrapping paper is attached onto the Mo electrode (P-side electrode 4P). In this manner, Example 1 was prepared. In the above preparation, Ag was used for the medicine wrapping paper. 2+δ S x Se 1-x After forming a film of Ag, the ionic liquid is soaked into the medicine paper. 2+δ S x Se 1-x Alternatively, a film may be formed.

[0051] The element of Example 2 of the present invention is an Ag film having a different δ value from that of Example 1, which is formed by changing the film forming conditions of the molecular beam deposition apparatus and using the molecular beam deposition method (MBD method). 2+δ S 0.75 Se 0.25 The other conditions for fabricating the element were the same as those in Example 1. Example Ag 2+δ S x Se 1-x The semiconductor layer is a single phase. (a), (b), and (c) of FIG. 13 and (a) and (b) of FIG. 14 are, respectively, Ag2S 0.6 Se 0.4 ,Ag2S 0.45 Se 0.55 ,Ag2S 0.5 Se 0.5,Ag2S 0.10 Se 0.90 ,Ag 2+δ S 0.75 Se 0.25 The results of thin film X-ray diffraction experiments are shown below. Using a Cu tube, the incident angle was set to 0 degrees, and 2θ-θ measurements (general symmetric measurements) were performed in the range of 2θ = 20 to 100 degrees. The results showed that Ag2S 0.6 Se 0.4 ,Ag2S 0.45 Se 0.55 ,Ag2S 0.5 Se 0.5 ,Ag2S 0.10 Se 0.90 ,Ag 2+δ S 0.75 Se 0.25 It was confirmed that the Ag-S-Se film is a single-phase film with high crystallinity. Since the film is formed on a Si substrate, a diffraction peak originating from the Si substrate is detected at around 33 degrees (composition analysis such as surface SEM-EDX has confirmed that the Ag-S-Se film does not contain Si). Thin-film X-ray diffraction (grazing incidence X-ray diffraction) with an incidence angle of 1 degree was also performed, confirming that the Ag-S-Se film is a single-phase film.

[0052] All of the Ag-S-Se films shown as examples are crystalline materials, and are thin film materials that exhibit extremely low thermal conductivity of less than 1 W / mK at room temperature under zero bias (when no external voltage is applied). (Note that when measuring the thermal conductivity of thin films in the film thickness direction, the time-domain thermoreflectance method (TDTR method) was used, and it was confirmed that the Ag-S-Se films exhibit extremely low thermal conductivity of less than 1 W / mK at room temperature.)

[0053] In the present invention, the heat flow switching characteristic evaluation employs a cyclic heating method for measuring the thermal conductivity in the in-plane direction. In the cyclic heating method, a P-side electrode 4P of Mo formed by sputtering on a substrate 5 of a glass substrate and a Ag2S film formed by MBD are x Se 1-xA terminal of an external power source V was attached to the N-side electrode 4N of the Cu plate placed on the N-type semiconductor layer 2N of the substrate 5, and a voltage was applied. Heating was performed periodically using a heater H placed on the N-type semiconductor layer 2N, and the temperature of the sample surface was measured using a thermal camera C. The thermal conductivity of the substrate 5 in the in-plane direction was calculated from the temperature change.

[0054] As a result of the above measurement, in Example 1, a linear increase in thermal conductivity along the bias voltage from −0.2 V to +0.4 V was confirmed as shown in Fig. 12. The measurement of the cyclic heating method in Example 1 was carried out in the air. The direction of bias application is defined as positive from the P-side electrode 4P (Mo electrode) to the N-type semiconductor layer. When a voltage of -0.2 V was applied, the thermal conductivity was 0.48 W / mK, whereas when a voltage of +0.4 V was applied, the thermal conductivity was 0.65 W / mK, confirming an increase in thermal conductivity of about 35%. 15(a) shows the raw data of Example 1 in which the change in thermal conductivity was measured by the cyclic heating method (the frequency during cyclic heating was 30 mHz). Positions A and B indicate the measurement positions when the thermal conductivity was measured by the cyclic heating method, and positions A and B are spaced 0.072 mm apart in the in-plane direction. As a result, the phase delay ΔΦ when -0.2V is applied -0.2V The phase lag ΔΦ when +0.4V is applied is 0.4V It can be seen that the thermal conductivity increases when a voltage of +0.4 V is applied.

[0055] In Example 2, the thermal conductivity was 0.35 W / mK when a voltage of -0.4 V was applied, whereas the thermal conductivity was 0.70 W / mK when a voltage of +0.2 V was applied, confirming a two-fold (100%) increase in thermal conductivity. Figure 15(b) shows the raw data of Example 2, in which the change in thermal conductivity was measured by the cyclic heating method. The measurement conditions for the cyclic heating method in Example 2 were the same as those in Example 1. As a result, the phase delay ΔΦ when -0.4V is applied -0.4V The phase lag ΔΦ when +0.2V is applied is 0.2V is smaller, and it can be seen that the thermal conductivity increases when a voltage of +0.2 V is applied. Thus, in the embodiment of the present invention, it is seen that the thermal conductivity is significantly increased by a small bias voltage of 1 V or less. 2+δ S x Se 1-x The increase in thermal conductivity is believed to be due to the increase in electronic thermal conductivity caused by charges induced at the interface of the N-type semiconductor layer.

[0056] Next, a device according to Example 3 of the present invention was fabricated as follows. First, in Example 3, a 50 nm thick Au electrode was formed on a glass substrate by sputtering, and this Au electrode was used as a P-side electrode. In addition, Ag was deposited on a 100 μm thick drug packaging paper by molecular beam deposition (MBD). 2+δ S 0.75 Se 0.25 The Ag film was deposited at 960 nm. 2+δ S x Se 1-x is defined as an N-type semiconductor layer. Next, write C8H on this medicine paper. 11 By soaking the paper in F6N3O4S2 (ionic liquid), a porous body (medicine wrapping paper) containing the ionic liquid was formed. Furthermore, the medicine wrapping paper containing the ionic liquid was attached and adhered onto an Au electrode (positive electrode), thereby producing the element of Example 3.

[0057] For this Example 3 of the present invention, the cyclic heating method was adopted to measure the thermal conductivity in the in-plane direction, and the heat flow switching characteristics were evaluated, similarly to Examples 1 and 2. The measurement by the cyclic heating method in Example 3 was carried out in a vacuum. The measurement results confirmed a linear increase in thermal conductivity along with the bias voltage from 0 V to +2.4 V, as shown in FIG. When a voltage of 0 V was applied, the thermal conductivity was 0.5 W / mK, whereas when a voltage of +2.4 V was applied, the thermal conductivity was 0.94 W / mK, confirming an increase in thermal conductivity of 1.9 times the heat flow switching performance.

[0058] As for Example 3 of the present invention, similarly to Examples 1 and 2, the raw data of Example 3 in which the change in thermal conductivity was measured by the cyclic heating method is shown in FIG. The frequency during cyclic heating was 300 mHz. Positions A and B were spaced 0.324 mm apart in the in-plane direction. As a result, the phase delay ΔΦ when the bias voltage is 0V 0V The phase lag ΔΦ when +2.4V is applied is 2.4V However, it has become smaller (ΔΦ 2.4V / ΔΦ 0V = 0.59), and it can be seen that the thermal conductivity increases when a voltage of +2.4 V is applied. In Examples 1 and 2, the ionic liquid material of the insulator layer 3 was BF4-based (tetrafluoroborate-based) CH 20 In Example 3, the ionic liquid material for the insulator layer 3 is an imide-based [(CF3SO2)2N] - (Bis(trifluoromethanesulfonyl)imide) C8H 11 Since the imide-based material in Example 3 has a higher withstand voltage than the BF4-based materials in Examples 1 and 2, the heat flow switching element can be operated at a higher bias voltage.

[0059] The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0060] For example, when the insulator layer is made of a gel of an ionic liquid, the C8H 11 When F6N3O4S2[EMIM TFSI] is used as the ionic liquid, a gelled material can be obtained as shown below. First, P(VDF-HFP) as the polymer powder to be gelled and N,N-dimethylformamide as the organic solvent were mixed with the ionic liquid CH 11 By adding an appropriate amount to F6N3O4S2[EMIM TFSI], a mixture that will become the base for the above gel material is created. Next, the mixture that forms the base of the above gel material, PS(5000)-PNMA(75000)-PS(5000), and the organic solvent dichloromethane are mixed in a ratio of 7:1:270 and heat-treated at an appropriate temperature of about 60°C to obtain an ionic liquid gel material. A heat flow switching element can be produced by bonding an insulating layer of the gelled ionic liquid to a semiconductor layer prepared separately. [Explanation of symbols]

[0061] 1, 21, 31... heat flow switching element, 2N, 2P... semiconductor layer, 2P... P-type semiconductor layer, 2N... N-type semiconductor layer, 3... insulator layer, 4N... N-side electrode, 4P... P-side electrode, 5, 25... substrate

Claims

1. A semiconductor layer; an insulator layer laminated on the semiconductor layer, A heat flow switching element, characterized in that the insulator layer contains an ionic liquid.

2. 2. The thermal flow switching element according to claim 1, A P-type semiconductor layer; the insulator layer laminated on the P-type semiconductor layer; and an N-type semiconductor layer laminated on the insulating layer.

3. 3. The thermal flow switching element according to claim 2, an N-side electrode connected to the N-type semiconductor layer and made of a metal; a P-side electrode connected to the P-type semiconductor layer and made of a metal.

4. 3. The heat flow switching element according to claim 1, A heat flow switching element, wherein the insulator layer is a porous body containing the ionic liquid.

5. 3. The heat flow switching element according to claim 1, The semiconductor layer and the insulator layer are laminated on a substrate of a flexible insulating film directly or via another layer, the semiconductor layer and the insulator layer are flexible; A heat flow switching element characterized in that the entire element is in a sheet form.

6. 3. The heat flow switching element according to claim 1, A heat flow switching element, characterized in that the insulating layer is paraffin paper containing the ionic liquid.

7. 3. The heat flow switching element according to claim 1, The ionic liquid is ８ H ２０ NOBF ４ A heat flow switching element comprising:

8. 3. The heat flow switching element according to claim 1, The ionic liquid is ８ H １１ F ６ N ３ O ４ S ２ A heat flow switching element comprising:

9. 3. The heat flow switching element according to claim 1, A heat flow switching element comprising a plurality of said semiconductor layers and said insulating layers laminated alternately.

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