Patent Application
20080258690
1. Field of the Invention
The present invention relates to a thermal switching element that can control heat transfer and a method for manufacturing the thermal switching element.
2. Description of the Related Art
If there is a thermal switching element that can control heat transfer, the element is applicable in various fields. For example, the thermal switching element may be applied to the field of cooling technology for transferring heat in a specified direction. In this case, the element also can be called a cooling element.
Conventional cooling technologies can be classified into two major categories: a technology using the compression-expansion cycle of a coolant; and a technology using a thermoelectric phenomenon. For the technology using the compression-expansion cycle of a coolant, the coolant is compressed mainly with a compressor. This technology has the advantage of excellent efficiency resulting, e.g., from long years of technical improvements in compressors, and thus is applied widely to consumer appliances such as a freezer, refrigerator, and air conditioner. However, most of the coolant includes chlorofluorocarbon, and the environmental characteristics of chlorofluorocarbon have been a problem. Although an alternative to chlorofluorocarbon is being studied as the coolant at present, so far no coolant material has been developed that can exhibit heat transfer characteristics comparable to those of chlorofluorocarbon by the compression-expansion cycle.
On the other hand, an element (thermoelectric element) using a thermoelectric phenomenon provides cooling without any coolant. Therefore, this element not only can have excellent environmental characteristics, but also can be essentially maintenance free because a mechanical structure is not necessary. A typical example of the thermoelectric element is a Peltier element. However, the thermoelectric element is not applied to a refrigerator or air conditioner, although there are some exceptions, since the efficiency is low with the current technology. For example, when a coolant is used, the Carnot efficiency at operating temperatures (e.g., −25° C. to 25° C.) of a refrigerator or the like may be in the range of about 30% to 50%. However, the efficiency of the Peltier element is less than 10%. Moreover, a-potential thermoelectric element other than the Peltier element has not been developed yet.
Thus, there is a growing demand for a thermal switching element that can transfer heat without any coolant such as chlorofluorocarbon and is distinguished from a conventional thermoelectric element.
When the thermal switching element is combined, e.g., with a heat conductor, a heat insulator, or a heating element, it is also possible to provide a thermal solid-state circuit element having a structure and function similar to those of an electric circuit element. To control heat transfer, active control of electrons that transfer heat is required. In a conventional thermoelectric element, however, it is difficult to control the electrons actively. For example, a thermoelectric phenomenon is attributed to heat transfer caused by electrons that are transported while drifting in a material. The characteristics (thermoelectric characteristics) of the thermoelectric element generally are represented by a thermoelectric index ZT. The larger ZT is, the higher the efficiency of the element becomes. The, thermoelectric index ZT is expressed by a formula S2T/κp (where S is thermoelectric power, T is an absolute temperature, κ is a thermal conductivity, and ρ is a specific electric resistance). This formula indicates that the transport characteristics of electrons in the element significantly contribute to the thermoelectric characteristics. Accordingly, the electron density or the like may affect the thermoelectric characteristics of the element. However, it is difficult to actively control the electron transport characteristics of a conventional thermoelectric element such as a Peltier element.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a thermal switching element that can control heat transfer by having a quite different configuration from that of a conventional technique, and a method for manufacturing the thermal switching element.
A thermal switching element of the present invention includes a first electrode, a second electrode, and a transition body arranged between the first electrode and the second electrode. The transition body includes a material that causes an electronic phase transition by application of energy. The thermal conductivity between the first electrode and the second electrode is changed by the application of energy to the transition body.
A method for manufacturing a thermal switching element of the present invention is directed to a thermal switching element that includes a first electrode, a second electrode, a transition body arranged between the first electrode and the second electrode, and an insulator arranged between the transition body and the second electrode. The transition body includes a material that causes an electronic phase transition by application of energy. The insulator is formed of a vacuum. The thermal conductivity between the first electrode and the second electrode is changed by the application of energy to the transition body. The method includes (I) producing a space between the second electrode and the transition body by locating the second electrode and a laminate including the transition body and the first electrode at a predetermined distance apart so that the second electrode faces the transition body, and (II) forming an insulator between the second electrode and the transition body by maintaining the space under vacuum.
The method for manufacturing a thermal switching element of the present invention also may be referred to as a method for manufacturing the thermal switching element as described above that further includes an insulator, and the insulator is formed of a vacuum and arranged between the transition body and the second electrode.
A method for manufacturing a thermal switching element of the present invention is directed to a thermal switching element that includes a first electrode, a second electrode, a transition body arranged between the first electrode and the second electrode, and an insulator arranged between the transition body and the second electrode. The transition body includes a material that causes an electronic phase transition by application of energy. The insulator is formed of a vacuum. The thermal conductivity between the first electrode and the second electrode is changed by the application of energy to the transition body. The method may include (i) producing a space between the second electrode and the transition body by locating the second electrode and the transition body at a predetermined distance apart, (ii) forming an insulator between the second electrode and the transition body by maintaining the space under vacuum, and (ii) arranging the first electrode so that the transition body is located between the second electrode and the first electrode.
A method for manufacturing a thermal switching element of the present invention is directed to a thermal switching element that includes a first electrode, a second electrode, a transition body arranged between the first electrode and the second electrode, and an insulator arranged between the transition body and the second electrode. The transition body includes a material that causes an electronic phase transition by application of energy. The insulator is formed of a vacuum. The thermal conductivity between the first electrode and the second electrode is changed by the application of energy to the transition body. The method may include (A) forming a laminate by layering the first electrode, the transition body, a precursor made of a material that is mechanically broken more easily than the transition body, and the second electrode in the indicated order, (B) producing a space between the second electrode and the transition body by extending the laminate in the layering direction of the laminate so as to break the precursor and removing the broken precursor, and (C) forming an insulator between the second electrode and the transition body by maintaining the space under vacuum.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the identical elements are denoted by the same reference numerals, and the description may not be repeated.
In the thermal switching element 1 of the present invention, the thermal conductivity can be changed in any form by the application of energy to the transition body 3. For example, when energy is applied to the transition body 3, heat transfer between a pair of electrodes 2a and 2b may become easier or more difficult than that before the application of energy. In other words, the thermal switching element 1 may have two states: a state in which heat moves relatively easily between the electrodes 2a and 2b (i.e., heat transfer in the transition body 3 is relatively easy); and a state in which heat moves with relative difficulty between the electrodes 2a and 2b i.e., heat transfer in the transition body 3 is relatively difficult). When the former is identified as an ON state and the latter is identified as an OFF state, the thermal switching element 1 may be in either ON or OFF state by applying energy to the transition body 3. The thermal conductivity is preferably as small as possible in the OFF state. A change in thermal conductivity between the electrodes 2a and 2b with the application of energy to the transition body 3 may be in either linear or nonlinear form. For example, the applied energy with which the thermal conductivity changes may have a threshold value. Alternatively, a change in thermal conductivity may exhibit hysteresis for energy applied to the transition body 3. These forms of changes in thermal conductivity can be adjusted, e.g., by selecting a phase transition material included in the transition body 3. In this specification, the thermal switching element is in the ON state when heat transfer is relatively easy, while the thermal switching element is in the OFF state when heat transfer is relatively difficult.
The electronic phase transition is a phase transition where the state of electrons in a substance changes regardless of the presence or absence of a structural phase transition (any change in structure itself of the substance, e.g., from solid to liquid). Therefore, the transition body 3 also may include a material whose electronic state is changed by the application of energy. The thermal switching element 1 of the present invention can control heat transfer by changing the state of electrons in the transition body 3.
The heat conduction of a solid material is expressed generally by the sum of a component due to phonon contribution and a component due to electron conduction contribution. The component due to phonon contribution can be a thermal component that is conducted by the lattice vibration of a substance, and the degree of conduction of the thermal component is referred to as lattice thermal conductivity. The component due to electron conduction contribution can be a thermal component that is conducted by the movement of electrons in a substance, and the degree of conduction of the thermal component is referred to as electronic thermal conductivity. The electronic phase transition involves a change in the state of electrons in a substance. Therefore, the thermal switching element 1 of the present invention also can be regarded as an element in which at least the electronic thermal conductivity of the transition body 3 is changed by the application of energy. Such a change in electronic thermal conductivity of the transition body 3 with the application of energy is used to control heat transfer between the electrodes 2a and 2b.
An insulator-metal transition is an example of the electronic phase transition. Thus, the transition body 3 may cause an insulator-metal, transition by the application of energy in the thermal switching element 1 of the present invention. After the transition body 3 has changed to the metallic state, the whole of the transition body 3 is not necessarily a metallic phase, but part of the transition body 3 may include a metallic phase. In view of the characteristics of the thermal switching element, when the transition body 3 undergoes the insulator-metal transition, the thermal conductivity of the transition body 3 in the insulator state is preferably as small as possible. That is, the lattice thermal conductivity of the transition body 3 is preferably as small as possible. The smallest possible lattice thermal conductivity of the transition body 3 is preferred even if the transition body 3 does not cause an insulator-metal transition.
As described above, the thermal switching element 1 of the present invention can control heat transfer via electrons by applying energy to the transition body 3. In this case, the heat transfer may be controlled via thermions. That is, when heat moves relatively easily between the electrodes 2a and 2b (i.e., heat transfer in the transition body 3 is relatively easy: ON state), it may be relatively easy for thermions to move in the transition body 3. When heat moves with relative difficulty between the electrodes 2a and 2b (i.e., heat transfer in the transition body 3 is relatively difficult: OFF state), it may be relatively difficult for thermions to move in the transition body 3. In the thermal switching element 1 of the present invention, such a change in movement of the thermions is attributed to the electronic phase transition caused by the application of energy to the transition body 3.
In this embodiment, the thermions mean “electrons that involve heat transfer”. In many cases, thermions generally indicate electrons emitted from the surface of a heated metal or semiconductor. The electrons passing through the transition body 3 of the thermal switching element 1 of the present invention are not limited to the general thermions, but can be electrons that involve heat transfer. The thermal switching element of the present invention was not achieved until the following were taken into consideration: the transition body arranged between the electrodes to control heat transfer by the application of energy, the combination of materials for each layer such as the transition body, the configuration or arrangement of each layer, and the like.
Therefore, the thermal switching element of the present invention is considered quite different in configuration from a superconducting switch as disclosed, e.g., in JP 01(1989)-216582 A. The superconducting state described in JP 01(1989)-216582 A is physically similar to the superfluid state and has ideal heat insulation properties. Thus, it may be difficult for the superconducting switch of the above document to control heat transfer, which can be performed by the thermal switching element of the present invention. In contrast, the transition body 3 of the thermal switching element 1 of the present invention may be in the normal conducting state (i.e., not in the superconducting state) when electrons move relatively easily.
In the thermal switching element 1 of the present invention, energy applied to the transition body 3 is not particularly limited. For example, at least one selected from electric energy, light energy, mechanical energy, magnetic energy, and thermal energy may be applied to the transition body 3. The choice of which energy to use depends on the type of a phase transition material included in the transition body 3. Two or more types of energy may be applied to the transition body 3. In this case, it is possible to apply the two or more types of energy either simultaneously or in the order of their types as needed. For example, electric energy may be applied first to the transition body 3, followed by light energy, mechanical energy, or the like. There is no particular limitation to a method for applying each type of energy.
The application of electric energy to the transition body 3 may be performed, e.g., by injecting electrons or holes (positive holes) into the transition body 3 or by inducing electrons or holes in the transition body 3. The injection or induction of electrons or holes may be performed, e.g., by producing a potential difference between the electrodes 2a and 2b, and specifically, e.g., by applying a voltage between the electrodes 2a and 2b. More specific examples of the configuration to apply electric energy and examples of the configuration to apply other types of energy will be described later.
The shape or size of the thermal switching element 1 is not particularly limited and may be determined arbitrarily in accordance with the necessary characteristics of the thermal switching element 1. As shown in
The transition body 3 of the thermal switching element 1 of the present invention will be described below. The transition body 3 may include, e.g., any of the following materials as a phase transition material.
The transition body 3 may include, e.g., an oxide with a composition expressed by AxDyOz, where A is at least one element selected from the group consisting of alkali metal (Group Ia), alkaline-earth metal (Group IIa), Sc, Y, and rare-earth element (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er), D is at least one transition element selected from the group consisting of Groups IIa, IVa, Va, VIa, VIIa, VIII, and Ib, and O is oxygen. The groups of elements are described based on IUPAC (1970) in this specification. According to IUPAC (1989), the at least one transition element is selected from Groups 3, 4, 5, 6, 7, 8, 9, 10, and 11. The oxide generally has a crystal structure in which the element D is located basically at a central position in a unit cell of the corresponding crystal lattice, and the atom at the central position is surrounded by a plurality of oxygen atoms.
There is no particular limitation to x, y, and z as long as they are positive numbers. Above all, x, y, and z are preferably numerical values that satisfy the following combinations. The oxides can be classified into a plurality of categories depending on the combinations. The transition body 3 may include an oxide that belongs to each of the categories. The values of x, y, and z of an oxide that belongs to each of the categories do not necessarily satisfy fully the following values (including examples). For example, an oxide may be partially deficient in oxygen or may be doped with a small amount of elements (e.g., the elements of Groups IIa to Vb) other than the elements A and D. The following categories are not established as common knowledge in the technical field of the present invention, but provided for convenience to make a clear explanation of the oxides.
In this category, x, y, and z satisfy x=n+2, y=n+1, and z=3n+4, where n is 0, 1, 2, or 3.
Examples of the oxide belonging to this category include oxides having an xyz index of (214) such as Sr2RuO4 and (La, Sr)2CoO4, and oxides having an xyz index of (327) such as Sr3Ru2O7 and (La, Sr)3Mn207. These oxides exhibit a so-called Ruddlesden-Popper structure.
When n=0, this category may include oxides in which the element D is placed at the position of the element A and/or the element A is placed at the position of the element D. Examples of such oxides may be an oxide with a composition expressed by DxAyOz and an oxide with a composition expressed by DxDyOz. Specifically this category may include, e.g., oxides having a spinel structure such as Mg2TiO4, Cr2MgO4, and Al2MgO4 (xyz index (214)), and oxides (xyz index (214)) that do not contain the element A such as Fe2CoO4 and Fe2FeO4 (i.e., Fe3O4).
In this category, x, y, and z satisfy x=n+1, y=n+1, and z=3n+5, where n is 1, 2, 3, or 4. Examples of the oxide belonging to this category include oxides having the partial intercalation of oxygen.
In this category, x, y, and z satisfy x=n, y=n, and z=3n, where n is 1, 2, or 3. When n=1, examples of the oxide belonging to this category include oxides having a perovskite crystal structure such as SrTiO3, BaTiO3, KNbO3, LiNbO3, SrMnO3, and SrRuO3. When n=2, examples of the oxide that belongs to this category include oxides having an xyz index of (226) such as Sr2FeMoO6 and SmBaMn2O6.
In this category, x, y, and z satisfy x=n+1, y=n, and z=4n+1, where n is 1 or 2. When n=1, examples of the oxide belonging to this category include oxides having an xyz index of (215) such as Al2TiO5 and Y2MoO5. When n=2, examples of the oxide that belongs to this category include oxides such as SrBi2Ta2O9.
In this category, x, y, and z satisfy x=0 or 1, y=0 or 1, and z=1, where either x or y is 0. Examples of the oxide belonging to this category include BeO, MgO, BaO, CaO, NiO, MnO, CoO, CuO, and ZnO.
In this category, x and y satisfy x=0, 1, or 2, y=0, 1, or 2, where either x or y is 0, and if x is 0, z is obtained by adding 1 to y, and if y is 0, z is obtained by adding 1 to x. Examples of the oxide belonging to this category include TiO2, VO2, MnO2, GeO2, CeO2, PrO2, SnO2, Al2O3, V2O3, Ce2O3, Nd2O3, Ti2O3, Sc2O3, and La2O3.
When x=0 or 2, y=0 or 2, and z=5, examples of the oxide may be Nb2O5, V2O5, and Ta2O5, where either x or y is 0.
The transition body 3 may include two or more types of the above oxides. For example, the transition body 3 may include oxides having a superlattice as a combination of a structural unit cell and a small unit cell of the oxides with different values of n in the same category. Specific categories may be, e.g., the category 1 (the oxides having a Ruddlesden-Popper structure) and the category 2 (the oxides having the intercalation of oxygen). The crystal lattice structure of such oxides having a superlattice is formed so that, e.g., oxygen octahedral layers of a single or plural elements D are separated by at least one block layer including the element A and oxygen.
The transition body 3 may include a strongly correlated electron material, e.g., a Mott insulator.
The transition body 3 may include a magnetic semiconductor. As a base material of the magnetic semiconductor, e.g., a compound semiconductor can be used. Specifically, examples of the compound semiconductor include the following: compound semiconductors of Groups I-V, I-VI, II-IV, II-V, II-VI, III-V, III-VI, IV-IV, I-III-VI, I-V-VI, II-III-VI, and II-IV-V such as GaAs, GaSe, AlAs, InAs, AlP, AlSb, GaP, GaSb, InP, InSb, In2Te3, ZnO, ZnS, ZnSe, ZnT, CdSe, CdTe, CdSb, HgS, HgSe, HgTe, SiC, GeSe, PbS, Bi2Te3, Sb2Se3, Mg2Si, Mg2Sn, Mg3Sb2, TiO2, CuInSe2, CuHgIn4, ZnIn2Se4, CdSnAs2, AgInTe2, AgSbSe2, GaN, AlN, GaAlN, BN, AlBN, and GaInNAs. Any of these compound semiconductors is used as a base material, to which at least one element selected from Groups IVa to VIII and IVb is added, thereby providing a magnetic semiconductor.
Alternatively, it is also possible to use a magnetic semiconductor with a composition expressed by Q1Q2Q3, where Q1 is at least one element selected from Sc, Y, a rare earth element (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, or Er), Ti, Zr, Hf, V, Nb, Ta, Cr, Ni, and Zn, Q2 is at least one element selected from V, Cr, Mn, Fe, Co, and Ni, and Q3 is at least one element selected from C, N, O, F, and S. The composition ratio of the elements Q1, Q2, and Q3 is not particularly limited.
Alternatively, it is also possible to use a magnetic semiconductor with a composition expressed by R1R2R3, where R1 is at least one element selected from B, Al, Ga, and In, R2 is at least one element selected from N and P, and R3 is at least one element selected from Groups IVa to VIII and IVb. The composition ratio of the elements R1, R2, and R3 is not particularly limited.
Alternatively, it is also possible to use a magnetic semiconductor with a composition expressed by ZnOR3, where R3 is the same as that described above, Zn is zinc, and O is oxygen. The composition ratio of the elements Zn, O, and R3 is not particularly limited.
Alternatively, it is also possible to use a magnetic semiconductor with a composition expressed by TOR3, where T is at least one element selected from Ti, Zr, V, Nb, Fe, Ni, Al, In, and Sn, R3 is the same as that described above, and O is oxygen. The composition ratio of the elements T, O, and R3 is not particularly limited.
The transition body 3 may include a material that causes a transition between metamagnetism and ferromagnetism by an externally applied electric field. For example, La (Fe, Si) or FeRh can be used. In this case, the application of electric energy allows the transition body 3 to cause an electronic phase transition.
When thermal energy is applied to the transition body 3 to cause an electronic phase transition, the transition body 3 may include, e.g., GaSb, InSb, InSe, Sb2Te3, GeTe, Ge2Sb2Te5, InSbTe, GeSeTe, SnSb2Te4, InSbGe, AgInSbTe, (Ge, Sn) SbTe, GeSb (Se, Te), or Te81Ge15Sb2S2.
The shape or size of the transition body 3 is not particularly limited and may be determined arbitrarily in accordance with the necessary characteristics of the thermal switching element 1. When the transition body 3 is formed in a layer as shown in
A material used for the electrodes 2a, 2b is not particularly limited as long as it is a conductive material. For example, a material having a linear resistivity of not more than 100 μΩ cm, specifically Cu, Al, Ag, Au, Pt, or TiN, can be used. If necessary, a semiconductor material also can be used. It is preferable that the semiconductor material has a small work function. The shape or size of the electrodes 2a, 2b is not particularly. limited and may be determined arbitrarily in accordance with the necessary characteristics of the thermal switching element 1.
Next, configuration examples of a thermal switching element of the present invention will be described.
The thermal conductivity of the insulator 4 is preferably smaller than that of the transition body 3 in the OFF state (e.g., when the transition body 3 undergoes an insulator-metal transition, it is in the insulator state). Thus, the thermal switching element 1 can achieve higher efficiency.
In the thermal switching element 1 including the insulator 4 as shown in
The insulator 4 may be formed, e.g., of a vacuum. When the insulator 4 is formed of a vacuum, the configuration of the element can be simplified. A method for producing the thermal switching element including the insulator 4 formed of a vacuum will be described later. In this case, a vacuum may be an atmosphere in which the pressure is, e.g., about 1 Pa or less. For the insulator 4 formed of a vacuum, thermions may be transported basically by thermionic transport. Depending on the thickness of the insulator 4, there may be some thermions transported by tunnel transport.
A general solid insulating material, e.g., ceramics such as an oxide or resin, can be used as the insulator 4. In this case, it is preferable that an amorphous or microcrystalline insulator is used as the insulator 4. In this specification, the microcrystalline state indicates that crystal grains having an average grain size of not more than 10 nm are dispersed in an amorphous base. When a solid insulator is used, the insulator 4 is preferably formed of a tunnel insulator. For the insulator 4 formed of a tunnel insulator, thermions that carry heat may be transported by tunnel transport. To form the tunnel insulator, e.g., a general material with tunnel insulating properties can be used. Specific examples of the material include an oxide, nitride, and oxynitride of Al, Mg, or the like. The thickness of the insulator 4 formed of a tunnel insulator is, e.g., in the range of 0.5 nm to 50 nm, and preferably in the range of 1 nm to 20 nm.
As the insulator 4, e.g., an inorganic polymer material also can be used. Examples of the inorganic polymer material include a silicate material and aluminum silicate material.
The inorganic polymer material in
For the inorganic polymer material in
The inorganic polymer material in
The insulator 4 is not limited to the inorganic polymer material and may be an insulating material that includes the similar hollow regions of, e.g., continuous or separate voids. Such an insulating material can provide the effect comparable to that of the inorganic polymer material. The insulating material can be produced, e.g., by a method in which powder is prepared as a base material and then fired, chemical foaming, physical foaming, or sol-gel process. However, the insulating material preferably includes a myriad of voids having an average diameter of about several nm to several tens of nm. Like the inorganic polymer material, the insulating material also may include electron emission materials, and thus can provide the effect comparable to that of the inorganic polymer material.
Specifically, e.g., dried gel produced by the sol-gel process may be used. The dried gel is a nano-porous body that includes a framework made up of particles having an average particle diameter of about several nm to several tens of nm and continuous hollow regions having an average diameter of about not more than 100 nm. A preferred material for the gel is, e.g., a semiconductor material or insulating material in view of the efficient electric field concentration, and particularly silica (silicon oxide) is suitable. A method for producing a porous silica gel, which is the dried gel including silica, will be described later.
A material for the electrode 8 may be the same as that for the electrodes 2a, 2b. In particular, a material having a small work function (e.g., not more than 2 eV) relative to the vacuum level is suitable. Specifically, e.g., a Cs compound or alkaline-earth metal compound can be used. The use of such materials allows thermions to be supplied more efficiently to the insulator 4.
The shape or size of the electrode 8 is not particularly limited and may be determined arbitrarily in accordance with the necessary characteristics of the thermal switching element 1. When the electrode 8 is formed in a layer as shown in
If necessary, another material may be arranged further between each of the layers of the thermal switching element 1 as shown in
Next, a method for applying energy to the transition body of a thermal switching element of the present invention will be described.
A material for the electrode 10 may be the same as that for the electrodes 2a, 2b. A material for the insulator 9 is not particularly limited as long as it is an insulating material or semiconductor material. For example, the material for the insulator 9 may be a compound of at least one element selected from Groups IIa to VIa including Mg, Ti, Zr, Hf, V, Nb, Ta, and Cr, lanthanide (including La and Ce), and Groups IIb to IVb including Zn, B, Al, Ga, and Si and at least one element selected from F, O, C, N, and B. Specifically, e.g., SiO2, Al2O3, or MgO can be used. As a semiconductor, e.g., ZnO, SrTiO3, LaAlO3, AlN, or SiC can be used.
The shape or size of the insulator 9 is not particularly limited. When the insulator 9 is formed in a-layer as shown in
A thermal switching element that includes the structure in
When magnetic energy is applied to the transition body 3, a flux guide for focusing a magnetic field generated in the electrode 10 may be arranged in contact with or in the vicinity of the electrode 10. The flux guide is useful to efficiently introduce the magnetic field 12 into the transition body 3, and thus the thermal switching element can achieve higher efficiency.
The shape of the flux guide is not particularly limited as long as it can focus a magnetic field generated in the electrode 10, and may be determined arbitrarily in accordance with the necessary characteristics of the thermal switching element, the requirements for the manufacturing process, or the like. For example, when the flux guide 13 is combined with the electrode 10, the cross section may be either rectangular (
A material for the flux guide 13 is not particularly limited as long as it can focus a magnetic field generated in the electrode 10; and may be a ferromagnetic material. Specifically, e.g., a soft magnetic alloy film that includes at least one element selected from Ni, Co, and Fe can be used.
It is preferable that the ferromagnetic material used for the flux guide 13 does not have an excessively large coercive force. When the ferromagnetic material with excessively large coercive force is used for the flux guide, there are possibilities that the control of a magnetic field applied to the transition body 3 is reduced due to the magnetization retention of the flux guide 13 itself, and that excessive energy is required to change the magnetization direction of the flux guide 13 itself and thus reduces the efficiency of the thermal switching element.
When the flux guides 13 are arranged in the vicinity of the transition body 3, the flux guides 13 may be divided as shown in
When the light 14 enters the transition body 3 via the electrode 2a and/or the electrode 2b, the electrode (the electrode 2b in
A method for applying thermal energy to the transition body 3 is not particularly limited to the example of
The deformable body 16 can be made, e.g., of a piezoelectric material or magnetostrictive material. When the deformable body 16 includes a piezoelectric material, e.g., a current flowing through the electrode 10 may be introduced into the deformable body 16. When the deformable body 16 includes a magnetostrictive material, e.g., a magnetic field generated by a current flowing through the electrode 10 may be introduced into the deformable body 16.
As is evident from the above explanation of a method for applying energy to the transition body 3, a plurality of different types of energy can be applied either simultaneously or in a specific order to the transition body 3 of the thermal switching element of the present invention. For example, the electrode 10 can be used for the application of different types of energy. If necessary, another material may be arranged further between each of the layers as shown in
The thermal switching element 1 of the present invention also can serve as a cooling element that conducts heat from one electrode selected from the electrodes 2a and 2b to the other electrode. For example, when a material that also has the function of an insulator is used for the transition body 3 of the thermal switching element in
For the thermal switching element 1 including the insulator 4 as shown in
Next, a method for manufacturing a thermal switching element of the present invention will be described.
The individual layers of a thermal switching element can be formed by a general thin film formation process. Examples of the process include various types of sputtering such as pulse laser deposition (PLD), ion beam deposition (IBD), cluster ion beam, RF, DC, electron cyclotron resonance (ECR), helicon, inductively coupled plasma (ICP), and facing target sputtering, molecular beam epitaxy (MBE), and ion plating. In addition to these PVD methods, e.g., CVD, plating, or a sol-gel process can be used as well. When microfabrication is necessary, general methods used for a semiconductor process or a magnetic head fabrication process may be combined. Specifically, e.g., physical or chemical etching techniques such as ion milling, reactive ion etching (RIE), and focused ion beam (FIB), a stepper technique for forming fine patterns, and photolithography with an electron beam (EB) method or the like can be used in combination. Moreover, chemo-mechanical polishing (CMP) or cluster ion beam etching may be used to flatten the surface of each layer (e.g., an electrode) or the like. The individual layers may be formed on a substrate. A material for the substrate is not particularly limited and may be, e.g., Si, SiO2, or oxide single crystals such as GaAs and SrTiO3.
The following is an explanation of a method for manufacturing the thermal switching element 1 in which the insulator 4 is in the vacuum state and arranged between the transition body 3 and the electrode 2b, as shown in
In the example of
The predetermined distance in the step (I) may correspond, e.g., to the necessary thickness of a vacuum insulating portion to be formed. Specifically, the predetermined distance may be, e.g., not more than 50 nm, and preferably not more than 15 nm, as described above. The lower limit of the distance is not particularly limited and may be, e.g., not less than 0.3 nm.
In the step (I), there is no particular limitation to a method in which the electrode 2b and the laminate are located at a predetermined distance apart so that a space is produced between the electrode 2b and the transition body 3. For example, the laminate and/or the electrode 2b may be moved while controlling the distance between them, which can be performed in any manner. Specifically, e.g., a piezoelectric body 17 is arranged to move the electrode 2b and/or the laminate (step (I-a)), and then the piezoelectric body 17 is deformed (step (I-b)), as shown in
In the step (I-a), there is no particular limitation to a method for arranging the piezoelectric body 17 as long as the electrode 2b and/or the laminate can be moved. For example, the piezoelectric body 17 may be arranged in contact with the electrode 2b and/or the laminate, as shown in
In the step (II), there is no particular limitation to a method for maintaining the space produced in the step (I) under vacuum. For example, the space may be evacuated to create a vacuum and then sealed while keeping the distance between the laminate and the electrode 2b after the step (I). To maintain the space under vacuum, e.g., the whole of the laminate and the electrode 2b may be placed in a vacuum atmosphere. It is also possible to perform the steps (I) and (II) simultaneously. For example, the steps (I) may be performed in a vacuum atmosphere, and a space produced between the laminate and the electrode 2b may be sealed in the same atmosphere. When the step (I) includes two or more processes, the whole of the laminate and the electrode 2b may be placed in a vacuum atmosphere during the step (I). As described above, a vacuum may be an atmosphere in which the pressure is, e.g., about 1 Pa or less.
In the example of
The methods for producing the space and the vacuum insulating portion in the steps @) and (ii) may be the same as those in the steps (I) and (II), respectively. For example, the step (i) may include a step (i-a) in which the piezoelectric body 17 is arranged to move at least one selected from the electrode 2b and the transition body 3 and a step (i-b) in which the piezoelectric body 17 is deformed so that the electrode 2b and the transition body 3 are located at a predetermined distance apart, and a space is produced between the electrode 2b and the transition body 3.
There is no particular limitation to a method for arranging the electrode 2a in the step (iii), and any of the above thin film formation processes can be used. The step W is not necessarily performed after the step (ii) and may be performed, e.g., at any time between the beginning of the step (i) and the end of the step (ii).
First, a multilayer film that includes the electrode 2a, the transition body 3, the electrode 2b, and a precursor 18 instead of the vacuum insulating portion is formed as shown in
Next, as shown in
Subsequently, as shown in
There is no particular limitation to a method for forming the multilayer film in the step (A), and any of the above film formation processes can be used.
In the step (B), a method for extending the multilayer film in its layering direction is not particularly limited and may be performed, e.g., by using the piezoelectric body 17 as shown in
In the step (B-a), there is no particular limitation to a method for arranging the piezoelectric body 17 as long as the multilayer film can be extended. For example, the piezoelectric body 17 may be arranged in contact with the electrode 2b of the multilayer film, as shown in
In the step (B-b), the piezoelectric body 17 may either expand or shrink to extend the multilayer film. Alternatively, it is also possible to combine the expansion and shrinkage of the piezoelectric body 17. For example, when the piezoelectric body 17 expands and shrinks so that the amount of expansion is equal to the amount of shrinkage, a space can be produced while maintaining the same distance (between the transition body 3 and the electrode 2b) as the thickness of the precursor 18.
In the step (B), a method for removing the remaining precursor 18 is not particularly limited and may be performed, e.g., by blowing the gas 19 as shown in
In the step (C), there is no particular limitation to a method for maintaining the space produced in the step (B) under vacuum. For example, the space may be evacuated to create a vacuum and then sealed while keeping the distance between the transition body 3 and the electrode 2b after the step (B). To maintain the space under vacuum, e.g., the whole of the transition body 3, the electrode 2b, and the electrode 2a may be placed in a vacuum atmosphere. It is also possible to perform the steps (A) and/or (B) and the step (C) simultaneously. For example, the steps (A) and (B) may be performed in a vacuum atmosphere, and a space produced between the transition body 3 and the electrode 2b may be sealed in the same atmosphere. Further, the whole of the transition body 3, the electrode 2a, and the electrode 2b may be placed in a vacuum atmosphere at any time between the beginning of the step (A) and the end of the step (B). As. described above, a vacuum may be an atmosphere in which the pressure is, e.g., about 1 Pa or less.
The following is an example of a method for producing a nano-porous body used for the insulator 4. A method for producing porous silica will be described as an example of the nano-porous body.
The method for producing porous silica can be divided into two major steps: a step of producing a wet gel, and a step of drying the wet gel (drying process).
First, the step of producing a wet gel will be described. A silica wet gel can be synthesized, e.g., by mixing materials for silica in a solvent and allowing the mixture to undergo a sol-gel reaction. In this case, a catalyst may be used as needed. During the formation of a wet gel, the materials react in the solvent to produce fine particles, the fine particles constitute a three-dimensional network, and thus a reticulate framework is formed. The shape (e.g., the average diameter of voids in the porous silica produced) of the framework can be controlled, e.g., by selecting the materials and the solvent composition or by adding a catalyst or viscosity modifier as needed. In the actual production process, the silica wet gel may be produced in the following manner: the silica materials mixed in the solvent are applied to a substrate and allowed to stand for a given time so that the silica material is gelatinized.
A method for applying the silica material to the substrate is not particularly limited, and any method such as spin coating, dipping, or screen printing may be selected in accordance with the necessary thickness, shape, or the like.
A temperature at which the wet gel is produced is not particularly limited and may be, e.g., in the vicinity of room temperature. If necessary, heating may be performed at a temperature not more than the boiling point of the solvent used.
Examples of the materials for silica include alkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, trimethoxymethylsilane, and dimethoxydimethylsilane, oligomer of these compounds, water glass compounds such as sodium silicate (silicate of soda) and potassium silicate, and colloidal silica. They may be used individually or as a mixture of two or more compounds.
The solvent is not particularly limited as long as it dissolves the materials to produce silica. For example, general inorganic/organic solvents such as water, methanol, ethanol, propanol, acetone, toluene, and hexane may be used individually or as a mixture of two or more solvents.
Examples of the catalyst include water, acids such as hydrochloric acid, sulfuric acid, and acetic acid, and bases such as ammonia, pyridine, sodium hydroxide, and potassium hydroxide.
The viscosity modifier is not particularly limited as long as it can adjust the viscosity of the solvent mixed with the materials. For example, ethylene glycol, glycerin, polyvinyl alcohol, or silicone oil can be used.
To disperse the electron emission materials in the porous silica, e.g., the electron emission materials as well as the above materials may be mixed and dispersed in the solvent, and then the mixture may be gelatinized.
Next, the step of drying the wet gel will be described. A method for drying the wet gel is not particularly limited. For example, normal drying such as air drying, drying by heating, and drying under reduced pressure, supercritical drying, or freeze drying can be used. In this case, the supercritical drying is preferred to suppress the shrinkage of the gel due to drying. Even if the normal drying is used, the surface of a solid-phase component of the wet gel may be treated so as to have water repellency, thereby suppressing the shrinkage of the gel due to drying.
The solvent that has been used in producing the wet gel can be used as a solvent for the supercritical drying. Alternatively, the solvent included in the wet gel may be substituted beforehand for a solvent that can be handled more easily in the supercritical drying. Any solvent generally used as a supercritical fluid, e.g., alcohols such as methanol, ethanol, and isopropyl alcohol, carbon dioxide, or water can be used for the substitute solvent. Moreover, the solvent included in the wet gel also may be substituted beforehand for acetone, isoamyl acetate, hexane, or the like that are eluted easily with the supercritical fluid.
The supercritical drying may be performed, e.g., in a pressure vessel such as an autoclave. When methanol is used as the supercritical fluid, the wet gel may be dried by maintaining the inside of the autoclave at a pressure of not less than 8.09 MPa and a temperature of not less than 239.4° C., which are the critical conditions of methanol, and by gradually releasing the pressure while the temperature is kept constant. Similarly, when carbon dioxide is used as the supercritical fluid, the wet gel may be dried by maintaining the inside of the autoclave at a pressure of not less than 7.38 MPa and a temperature of not less than 31.1° C. and by gradually releasing the pressure while the temperature is kept constant. Similarly, when water is used as the supercritical fluid, the wet gel may be dried by maintaining the inside of the autoclave at a pressure of not less than 22.04 WPa and a temperature of not less than 374.2° C. and by gradually releasing the pressure while the temperature is kept constant. The drying time may be, e.g., not less than the time it takes for the solvent in the wet gel to be replaced at least one time by the supercritical fluid.
For a method that includes water repellent treatment of the wet gel before drying, a surface treating agent used for the water repellent treatment may react chemically on the surface of a solid-phase component of the wet gel, and then the wet gel may be dried. The water repellent treatment can reduce surface tension generated in the voids of the wet gel, so that the shrinkage of the gel during drying can be suppressed.
Examples of the surface treating agent include a halogen-based silane treating agent such as trimethylchlorosilane or dimethyldichlorosilane, an alkoxy-based silane treating agent such as trimethylmethoxysilane or trimethylethoxysilane, a silicone-based silane treating agent such as hexamethyldisiloxane or dimethylsiloxane oligomer, an amine-based silane treating agent such as hexamethyldisilazane, and alcohol-based treating agent such as propyl alcohol or butyl alcohol. Any other materials also can be used as long as they provide the effect comparable to that of the above surface treating agents.
The use of an inorganic material or organic polymer material also can produce the same nano-porous body. For example, any material generally used in forming ceramics such as aluminium oxide (alumina) can be used. After the nano-porous body is produced by the above method, the electron emission materials may be dispersed, and formed inside the nano-porous body using, e.g., a vapor synthetic method.
Hereinafter, the present invention will be described more specifically by way of examples. The present invention is not limited to the following examples.
In Example 1, a thermal switching element 1 as shown in
First, a resist 20 was deposited on SrTiO3 crystals that served as the transition body 3 (
Using the thermal switching element 1 thus produced, electric energy was applied to the transition body 3 by applying a voltage between the electrode 10 and the transition body 3, and changes in thermal conductivity between-the electrodes 2a and 2b before and after the application of energy were examined. The thermal conductivity between the electrodes 2a and 2b was measured by a Harman method. The Harman method evaluates the state of heat conduction using a temperature difference between both ends of a sample caused by the application of a current to the sample. Specifically, the thermal conductivity can be determined by a formula STI/ΔT, where S is thermoelectric power (V/K), T is an average temperature (K) of the sample, I is a current value (A), and ΔT (K) is a temperature difference of the sample. Unless otherwise specified, the thermal conductivity was measured at room temperature. The same is true for the following examples.
The evaluation showed that when no voltage was applied between the electrode 10 and the transition body 3, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied between the electrode 10 and the transition body 3 was increased. When the applied voltage was several tens of volts, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a voltage.
Next, a thermal switching element 1 as shown in
Using the thermal switching element 1 thus produced, electric energy was applied to the transition body 3 by applying a voltage between the electrode 10 and the transition body 3, and changes in thermal. conductivity between the electrodes 2a and 2b before and after the application of energy were examined.
Consequently, when no voltage was applied between the electrode 10 and the transition body 3, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied between the electrode 10 and the transition body 3 was increased. When the applied voltage was 2.5 V, thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a voltage.
In Example 1, SrTiO3 was used for the transition body. When other materials such as LaTiO3, (La, Sr) TiO3, YTiO3, (Sm, Ca) TiO3, (Nd, Ca) TiO3, (Pr, Ca) TiO3, SrTiO3-d (0<d≦0.1), and (Pr1-xCax) MnO3 (0<x≦0.5) were used for the transition body 3, the same result was obtained as well. Moreover, oxides expressed by X1BaX22O6 (where X1 is at least one element selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb and X2 is Mn and/or Co) such as GdBaMn2O6 or oxides expressed by (V1-yX3y) Ox (where 0≦y≦0.5, 1.5≦x≦2.5, and X3 is at least one element selected from Cr, Mn, Fe, Co, and Ni) also provided the same result.
In Example 2, a thermal switching element 1 as shown in
First, SrTiO3 was used as a substrate 22, on which the SrRuO3 electrode 2a was formed by sputtering. Then, the Cr:SrTiO3 transition body 3 was formed on the electrode 2a, and the Pt electrode 2b was formed on the transition body 3. The transition body 3 and the electrode 2b also were formed by sputtering. The transition body 3 and the electrode 2a were formed in a heating atmosphere at about 450° C. to 700° C. The thicknesses of the electrode 2a, the transition body 3, and the electrode 2b were about 200 nm, about 300 nm, and about 2 μm, respectively.
Using the thermal switching element 1 thus produced, electric energy was applied to the transition body 3 by applying a voltage between the electrodes 2a and 2b, and changes in thermal conductivity between the electrodes 2a and 2b before and after the application of energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no voltage was applied between the electrodes 2a and 2b, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied between the electrodes 2a and 2b was increased. When the applied voltage was about 0.5 V, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a voltage. Moreover, the thermal conductivity of the thermal switching element 1 exhibited hysteresis. Therefore, even if a voltage applied between the electrodes 2a and 2b was reduced to zero after the thermal conductivity appeared, the thermal conductivity between the electrodes 2a and 2b was maintained without any change. Subsequently, the thermal conductivity between the electrodes 2a and 2b disappeared by applying a voltage opposite to the direction of the first applied voltage between the electrodes. This showed that a nonvolatile thermal switching element was achieved by selecting the material for the transition body 3. A thermal device with more reduced power consumption can be constructed by using the nonvolatile thermal switching element.
In Example 2, Cr:SrTiO3 was used for the transition body. When other materials such as SrZrO3, (La, Sr) TiO3, Y (Ti, V) O3, SrTiO3-d (0<d≦0.1), and (Pr1-xCax) MnO3 (0<x≦0.5) were used for the transition body 3, the same result was obtained as well. Moreover, oxides expressed by X1BaX22O6 (where X1 is at least one element selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb and X2 is Mn and/or Co) such as NdBaMn2O6 or oxides expressed by (V1-yX3y) Ox (where 0≦y≦0.5, 1.5≦x≦2.5, and X3 is at least one element selected from Cr, Mn, Fe, Co, and Ni) also provided the same result.
In Example 3, a thermal switching element 1 as shown in
The Nb:SrTiO3 was used as a substrate 22, on which the following thin films were deposited by laser ablation. The deposition was performed in an oxygen atmosphere in the range of 10 mmTorr to 500 mmtorr while heating at 450° C. to 700° C. First, SrTiO3 (thickness: 50 nm) was arranged on the substrate 22, and LaSrMnO3 (thickness: 100 nm) was arranged on the SrTiO3, thereby forming the transition body 3. Then, SrRuO3 (thickness: 10 nm) was arranged on the transition body 3. Next, Pt (thickness: 240 nm) was arranged on the SrRuO3 by sputtering. The sputtering was performed at 400° C. Subsequently, the laminate of SrRuO3 and Pt was microfabricated into the electrodes 2a and 2b, as shown in
Using the thermal switching element 1 thus produced) a magnetic field 12 was applied to the transition body 3 by allowing a current 11 to flow through the electrode 10, and changes in thermal conductivity between the electrodes 2a and 2b before and after the application of magnetic energy were examined. The thermal conductivity was measured in the same manner as Example 1. The current flowed through all the plurality of electrodes 10 in the same direction.
Consequently, when no current flowed through the electrode 10, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a current flowing through the electrode 10 was increased. When the current was about 2.5 mA per electrode 10, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a magnetic field.
In Example 3, (La, Sr) MnO3 was used for the transition body. When other materials such as (La, Sr)3Mn2O7, X42FeReO6, X42FeMoO6, (La, X4)2CuO4, (Nd, Ce)2CuO4, (La, X4)2NiO4, LaMnO3, YMnO3, (Sm, Ca) MnO3, (Nd, Ca) MnO3, (Pr, Ca) MnO3, (La, X4) FeO3, YFeO3, (Sm, X4) FeO3, (Nd, X4) FeO3, (Pr, X4) FeO3, (La, X4) CoO3, (Y, X4) VO3, (Bi, X4) MnO3, and SrTiO3-d (0<d≦0.1) were used for the transition body 3, the same result was obtained as well. In this case, X4 is at least one element selected from Sr, Ca, and Ba. Moreover, oxides expressed by X1BaX22O6 (where X1 is at least one element selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb and X2 is Mn and/or Co) such as SmBaMn2O6 or oxides expressed by (V1-yX3y) Ox (where 0≦y≦0.5, 1.5≦x≦2.5, and X3 is at least one element selected from Cr, Mn, Fe, Co, and Ni) also provided the same result.
In Example 4, a thermal switching element including the configuration as shown in
MgO was used as a substrate, on which the following thin films were layered by laser ablation. The layering was performed in an oxygen atmosphere in the range of 10 mmTorr to 500 mmTorr while heating at 450° C. to 700° C. First, ITO (Sn-doped In2O3 having a thickness of 50 nm) was layered on the substrate, and (Pr, Ca) MnO3 (thickness: 100 nm) was layered on the ITO, thereby forming the transition body 3. Next, Pt (thickness: 240 nm) was layered on SrRuO3 by sputtering. The sputtering was performed at 400° C. Subsequently, the laminate of SrRuO3 and Pt was microfabricated into the electrodes 2a and 2b. Thus, the thermal switching element was produced.
Using the thermal switching element thus produced, light energy was applied to the transition body 3 by allowing pulsed laser light (wavelength: 532 nm) to enter from the substrate side, and changes in thermal conductivity between the electrodes 2a and 2b before and after the application of light energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no light entered the transition body 3, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, pulsed laser light entered the transition body 3. When the transition body 3 was irradiated with an ultrashort pulse of 100 femtoseconds at about 0.5 W, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the irradiation of light. Even if the wavelength of the pulsed laser light was varied from the near-infrared region to the visible light region, the same result also was obtained.
In Example 5, a thermal switching element including the configuration as shown in
LiTaO3 was used as a substrate, on which the following thin films were formed by magnetron sputtering. The film formation was performed in an oxygen-argon mixed atmosphere (a partial pressure ratio Ar:O2=1:1) in the range of 10 mmTorr to 500 mmTorr while heating at 450° C. to 700° C. First, V2O3 (thickness: 50 nm) was formed on the substrate as the transition body 3. Next, Pt (thickness: 50 nm) was formed on the transition body 3 at 400° C., and then was microfabricated into the electrodes 2a and 2b. Subsequently, Ni—Cr alloy (thickness: 100 nm) Was formed by electron-beam evaporation as the resistor 15. Further, Au (thickness: 300 nm) was formed as the electrode 10.
Using the thermal switching element thus produced, the resistor 15 generated heat by allowing a current to flow through the electrode 10, and the generated heat was applied to the transition body 3. Then, changes in thermal conductivity between the electrodes 2a and 2b before and after the application of thermal energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no current flowed through the electrode 10, i.e., the resistor 15 did not generate heat, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a current flowing through the electrode 10 was increased. When the current was about 4 mA, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of heat.
In Example 5, V2O3 was used for the transition body. When other materials such as VOx (1.5≦x≦2.5), Ni (S, Se)2, EuNiO3, SmNiO3, (Y, X4) VO3, SrTiO3-d (0<d≦0.1), and (Pr1-xCax) MnO3 (0<x≦0.5) were used for the transition body 3, the same result was obtained as well. In this case, X4 is at least one element selected from Sr, Ca, and Ba. Moreover, oxides expressed by X1BaX22O6 (where X1 is at least one element selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb and X2 is Mn and/or Co) or oxides expressed by (V1-yX3y) Ox (where 0≦y≦0.5, 1.5≦x<2.5, and X3 is at least one element selected from Cr, Mn, Fe, Co, and Ni) also provided the same result.
In Example 6, a thermal switching element 1 as shown in
LiTaO3 (thickness: 0.8 μm), which is a kind of piezoelectric material, was used as the deformable body 16, on which the following thin films were provided by sputtering. The arrangement of each layer was performed in an argon-nitrogen mixed atmosphere (a partial pressure ratio Ar:N2=3:2) in the range of 0.1 mmTorr to 100 mmTorr while heating at 200° C. to 500° C. First, LaVO3 (thickness: 100 nm) was arranged on the deformable body 16 as the transition body 3. Next, Al (thickness: 1000 nm) was arranged on the transition body 3 so as to form the electrodes 2a and 2b. Further, Al (thickness: 1000 nm) was arranged on the surface of the deformable body 16 that was opposite to the surface in contact with the transition body 3 so as to form the electrode 10. The electrode 10 was in the form of a comb by using a photolithographic technique, as shown in
Using the thermal switching element 1 thus produced, the deformable body 16 was deformed by the application of a voltage with the electrode 10, and pressure resulting from the deformation was applied to the transition body 3. Then, changes in thermal conductivity between the electrodes 2a and 2b before and after the application of mechanical energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no voltage was applied to the deformable body 16, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied to the deformable body 16 was increased. When the applied voltage was about 0.5 V, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of pressure, which is a kind of mechanical energy.
In Example 6, LaVO3 was used for the transition body. When other materials such as (Y, X4) MnO3, (La, X4) MnO3, (Bi, X4) MnO3, (Bi, X4) TiO3, (Bi, X4)3Ti2O7, (Pb, X4) TiO3, SrTiO3-d (0<d≦0.1), and (Pr1-xCax) MnO3 (0<x≦0.5) were used for the transition body 3, the same result was obtained as well. In this case, X4 is at least one element selected from Sr, Ca, and Ba. Moreover, oxides expressed by X1BaX22O6 (where X1 is at least one element selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb and X2 is Mn and/or Co) such as SmBaMn2O6 or oxides expressed by (V1-yX3y) Ox (where 0≦y≦0.5, 1.5≦x≦2.5, and X3 is at least one element selected from Cr, Mn, Fe, Co, and Ni) also provided the same result. In Example 6, LiTaO3 was used as the deformable body 16. When other materials such as LiNbO3,(Ba, Sr) TiO3, and Pb (Zr, Ti) O3 were used as the deformable body 16, the same result was obtained as well.
In Example 7, a thermal switching element 1 including the insulator 4 as shown in
First, SrRuO3 (thickness: 200 nm) was provided on a SrTiO3 substrate as the electrode 2a. Then, SrTiO3 doped with Cr in the range of 0.1 at % to 10 at % (Cr:SrTiO3 having a thickness of 300 nm) was provided on the electrode 2a as the transition body 3. The electrode 2a and the transition body 3 were formed by laser ablation (at a substrate temperature of 450° C. to 700° C.).
Next, a porous silica layer (thickness: about 0.1 μm) was formed by the above sol-gel process and provided on the transition body 3 so as to form the insulator 4. The following is an explanation of a specific method for producing the porous silica layer.
A solution including a silica material was prepared by mixing tetramethoxysilane, ethanol, and ammonia aqueous solution (0.1 N) at a molar ratio of 1:3:4. Diamond particles having an average particle diameter of about 10 nm were dispersed in the solution as electron emission materials. After stirring the solution, it had a viscosity suitable for application. Then, the solution was applied to the transition body 3 in a thickness of about 0.1 μm by spin coating. Subsequently, the applied silica sol was polymerized and gelatinized by drying. The silica gel thus formed was evaluated using a high-resolution scanning electron microscope. The evaluation showed that a wet gel structure including a three-dimensional network of Si—O—Si bond was formed as shown in
Next, the wet gel thus produced was washed with ethanol and substituted with a solvent, which then was subjected to supercritical drying with carbon dioxide, thereby producing a porous silica layer. The supercritical drying was performed in such a manner that a pressure of 12 MPa and a temperature of 50° C. were maintained for four hours, then the pressure was released gradually to atmospheric pressure, and subsequently the temperature was reduced to room temperature. The dried sample was annealed at 400° C. in a nitrogen atmosphere, and thus adsorbates on the porous silica layer were removed.
The porosity of the porous silica layer evaluated using a Brunauer-Emmett-Teller (BET) method was about 92%. The average pore diameter of the porous silica layer also was estimated by the same technique, and the resultant value was about 20 nm.
A laminate including the electrode 2a, the transition body 3, and the insulator 4 thus produced was annealed at 400° C. in a hydrogen atmosphere. This annealing allows the surface of the diamond particles included in the porous silica layer to be hydrogenated, so that the diamond particles can be more activated as electron emission materials.
Finally, Pt (thickness: 2000 nm) was provided on the insulator 4 as the electrode 2b by sputtering.
Using the thermal switching element 1 thus produced, electric energy was applied to the transition body 3 by applying a voltage between the electrodes 2a and 2b, and changes in thermal conductivity between the electrodes 2a and 2b before and after the application of energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no voltage was applied between the electrodes 2a and 2b, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied between the electrodes 2a and 2b was increased. When the applied voltage was about 5 V the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a voltage.
The radiant current density between the two electrodes was measured at the time of appearance of the thermal conductivity, and the resultant value was several 10 mA/cm2. Moreover, the electrode 2a came into contact with Au that was kept at 30° C. while maintaining the thermal conductivity of the thermal switching element 1, and a change in temperature of the electrode 2a was measured. Consequently, a phenomenon was observed in which the temperature of the electrode 2a was reduced by about 30 degrees, i.e., was reduced to about 0° C. Thus, it was confirmed that the thermal switching element including the insulator 4 also functioned as a cooling element.
In Example 7, a thermal switching element 1 including the insulator 4 and the electrode 8 as shown in
First, SrRuO3 (thickness: 200 nm) was provided on a SrTiO3 substrate as the electrode 2a. Then, SrTiO3 doped with Cr in the range of 0.1 at % to 10 at % (Cr:SrTiO3 having a thickness of 300 nm) was provided on the electrode 2a as the transition body 3. Next, (Sr, Ca, Ba) CO3 (thickness: 50 nm) was arranged on the transition body 3 as the electrode 8, and a porous silica layer (thickness: 0.1 μm) was arranged on the electrode 8 in the same manner as described above so as to form the insulator 4. The electrode 2a, the transition body 3, and the electrode 8 were formed by laser ablation (at a substrate temperature of 450° C. to 700° C.). Finally, Pt (thickness: 2000 nm) was arranged on the insulator 4 as the electrode 2b by sputtering. Thus, the thermal switching element 1 as shown in
Using the thermal switching element 1 thus produced, electric energy was applied to the transition body 3 by applying a voltage between the electrodes 2a and 2b, and changes in thermal conductivity between the electrodes 2a and 2b before and after the application of energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no voltage was applied between the electrodes 2a and 2b, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied between the electrodes 2a and 2b was increased. When the applied voltage was about 1.8 V, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a voltage. Considering the fact that the voltage required for the thermal switching element that did not include the electrode 8 was about 5 V, the efficiency was improved two or more times by the use of the electrode 8.
The electrode 2a came into contact with Au that was kept at 30°0 C. while maintaining the thermal conductivity of the thermal switching element 1, and a change in temperature of the electrode 2a was measured. Consequently, a phenomenon was observed in which the temperature of the electrode 2a was reduced. Thus, it was confirmed that the thermal switching element including the insulator 4 also functioned as a cooling element.
In Example 7, the porous silica layer having a thickness of about 0.1 μm was used as the insulator 4. Even if the thickness of the insulator 4 ranged from about 0.05 μm to 10 μm, the same result was obtained as well. Since the optimum thickness of the insulator 4 may vary with the structure or material of the element, the thickness of the insulator 4 is not limited to the above range.
In Example 7, (Sr, Ca, Ba) CO3 was used as the electrode 8. When other materials such as (Sr, Ca, Ba)—O, Cs—O, Cs—Sb, Cs—Te, Cs—F, Rb—O, Rb—Cs—O, and Ag—Cs—O were used as the electrode 8, the same result was obtained as well.
In Example 8, a thermal switching element 1 as shown in
First, sapphire (Al2O3) was used as a substrate 22, on which the NaCo2O6 electrode 2a was formed by sputtering. Then, the Ca3Co4O9 transition body 3 was formed on the electrode 2a, and the NaCo2O6 electrode 2b was formed on the transition body 3. The transition body 3 and the electrode 2b also were formed by sputtering. The transition body 3 and the electrode 2a were formed in a heating atmosphere at about 450° C. to 850° C. The thicknesses of the electrode 2a, the transition body 3, and the electrode 2b were about 200 nm, about 300 nm, and about 2 μm, respectively.
Using the thermal switching element 1 thus produced, electric energy was applied to the transition body 3 by applying a voltage between the electrodes 2a and 2b, and changes in thermal conductivity between the electrodes 2a and 2b before and after the application of energy were examined. The thermal conductivity was measured in the same manner as Example 1.
Consequently, when no voltage was applied between the electrodes 2a and 2b, the thermal conductivity between the electrodes 2a and 2b was too small to be measured. Thereafter, a voltage applied between the electrodes 2a and 2b was increased. When the applied voltage was about 0.5 V, the thermal conductivity appeared. Thus, it was confirmed that the thermal switching element had the function of controlling heat transfer by the application of a voltage. Moreover, the thermal conductivity of the thermal switching element 1 exhibited hysteresis. Therefore, even if a voltage applied between the electrodes 2a and 2b was reduced to zero after the thermal conductivity appeared, the thermal conductivity between the electrodes 2a and 2b was maintained without any change. Subsequently, the thermal conductivity between the electrodes 2a and 2b disappeared by applying a voltage opposite to the direction of the first applied voltage between the electrodes. This showed that a nonvolatile thermal switching element was achieved by selecting the material for the transition body 3. A thermal device with more reduced power consumption can be constructed by using the nonvolatile thermal switching element.
In Example 8, Ca3Co4O9 was used for the transition body 3. When delafossite expressed by CuX5O2 (where X5 is at least one element selected from Al, In, Ga, and Fe) or the like was used for the transition body 3, the same result was obtained as well.
As described above, the present invention can provide a thermal switching element that has a quite different configuration from that of a conventional technique and can control heat transfer by the application of energy, and a method for manufacturing the thermal switching element.
There is no particular limitation to the application of the thermal switching element of the present invention as long as it is used in a portion that performs heat transfer, e.g., a heat dissipating portion of a semiconductor chip such as a CPU used in information terminals, a heat transfer portion of a freezer, refrigerator, or air conditioner, which are typical products as a heat engine, or a heat flow control portion of heat wiring. In this case, the thermal switching element of the present invention can be used not only in a portion that requires control of heat transfer, but also in a portion that merely transfers heat without controlling the heat transfer.
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-021841 | Jan 2003 | JP | national |
| 2003-324404 | Sep 2003 | JP | national |
This application is a division of U.S. Ser. No. 11/605,064, filed Nov. 28, 2006, which is a continuation of U.S. Ser. No. 10/865,130 filed Jun. 10, 2004, which is a continuation of International application PCT/JP2004/000845, filed Jan. 29, 2004, which applications are incorporated herewith by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11605064 | Nov 2006 | US |
| Child | 12157954 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10865130 | Jun 2004 | US |
| Child | 11605064 | US | |
| Parent | PCT/JP04/00845 | Jan 2004 | US |
| Child | 10865130 | US |
