JP2011222873A - Thermoelectric conversion element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a thermoelectric conversion element having a comparatively simple configuration and extremely high conversion efficiency.SOLUTION: Between a pair of electrodes 1 and 3, for example, a periodic structure 2 is provided which is formed by alternately laminating a plurality of semiconductor layers 2a such as n-type ZnO and a plurality of metal layers 2b such as Al, the thermoelectric conversion element is constituted by installing an insulating plate on the electrode 1 according to the necessity, and a heat generating source 4 abuts on the electrode 3 or the insulating plate.

Description

  The present invention relates to a thermoelectric conversion element that converts heat generated from a heat generation source into electricity and a method for manufacturing the same.

  Thermoelectric conversion elements that use the Seebeck effect to convert heat generated from a heat generation source into electricity are attracting attention as an energy-saving technology considering environmental issues from the viewpoint of waste heat utilization. A thermoelectric conversion element in a power plant or a thermoelectric conversion element for a wristwatch has already been put into practical use.

JP 2008-98197 A

However, thermoelectric conversion elements are not practically used in the mW to kW class, which is a medium output range. The cause is that the conversion efficiency of the thermoelectric conversion element is low. A figure of merit ZT used as a characteristic index of thermoelectric material (an index of conversion efficiency) is expressed as follows.
ZT = α2σT / Χ, Z∝m ^* μ / Χ
T: temperature, α: Seebeck coefficient, σ: electrical conductivity, Χ: thermal conductivity, m ^* : effective mass, μ: mobility

In order to increase the figure of merit ZT, the electrical conductivity of the thermoelectric conversion element may be increased and the thermal conductivity may be decreased. However, in conventional materials, the two are generally in a proportional relationship. Usually, the effective mass m ^* and the mobility μ are also inversely proportional. That is, with the conventional thermoelectric conversion element using a single material, it is extremely difficult to increase the figure of merit ZT, and as a result, a thermoelectric conversion element with high conversion efficiency has not yet been realized.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermoelectric conversion element having a relatively simple configuration and extremely high conversion efficiency, and a method for manufacturing the same.

  One aspect of the thermoelectric conversion element includes a periodic structure in which metal layers and semiconductor layers are alternately stacked, and a pair of electrode layers formed above and below the periodic structure.

  One aspect of a method for manufacturing a thermoelectric conversion element includes a step of alternately laminating metal layers and semiconductor layers to form a periodic structure, and a step of forming a pair of electrode layers above and below the periodic structure. including.

  According to each aspect described above, a thermoelectric conversion element with extremely high conversion efficiency can be realized with a relatively simple configuration.

It is a schematic sectional drawing which shows the manufacturing method of the thermoelectric conversion element by 1st Embodiment to process order. It is a schematic sectional drawing which shows the thermoelectric conversion element and heat generating source by 1st Embodiment. It is the schematic which shows the manufacturing method of the thermoelectric conversion element by the modification of 1st Embodiment in process order. It is a schematic sectional drawing which shows the manufacturing method of the thermoelectric conversion element by 2nd Embodiment to process order. It is a schematic sectional drawing which shows the thermoelectric conversion element and heat generating source by 2nd Embodiment. It is the schematic which shows the manufacturing method of the thermoelectric conversion element by the modification of 2nd Embodiment to process order. It is a schematic sectional drawing which shows the thermoelectric conversion element and heat generating source by 3rd Embodiment. It is a schematic perspective view which shows the manufacturing method of the thermoelectric conversion element by the modification of 3rd Embodiment in order of a process. It is sectional drawing which shows schematic structure of the thermoelectric conversion element by 4th Embodiment. It is sectional drawing which shows schematic structure of the other example of the thermoelectric conversion element by 4th Embodiment. It is sectional drawing which shows schematic structure of the other example of the thermoelectric conversion element by 4th Embodiment. It is sectional drawing which shows schematic structure of the other example of the thermoelectric conversion element by 4th Embodiment. It is sectional drawing which shows schematic structure of the other example of the thermoelectric conversion element by 4th Embodiment. It is sectional drawing which shows schematic structure of the other example of the thermoelectric conversion element by 4th Embodiment. It is sectional drawing which shows schematic structure of the thermoelectric conversion element by the modification of 4th Embodiment. It is sectional drawing which shows schematic structure of the electronic device by 5th Embodiment.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

(First embodiment)
In the present embodiment, the configuration of a thermoelectric conversion element having one periodic structure is disclosed together with its manufacturing method. The following manufacturing method is an example for obtaining the thermoelectric conversion element according to the present embodiment.
FIG. 1 is a schematic cross-sectional view showing the method of manufacturing a thermoelectric conversion element according to the first embodiment in the order of steps. FIG. 2 is a schematic cross-sectional view showing the thermoelectric conversion element and the heat source according to the first embodiment.

To manufacture a thermoelectric conversion element, first, as shown in FIG. 1A, a substrate 1 is prepared.
The substrate 1 is used as a substrate for forming a periodic structure described later, and also functions as one of a pair of electrodes of the thermoelectric conversion element. As the material of the substrate 1, a metal having a property capable of obtaining ohmic contact with the semiconductor layer constituting the periodic structure, such as Al or Cu, is used. Here, the substrate 1 is made of, for example, Al and has a thickness of about 100 μm.

Subsequently, as shown in FIG. 1B, the periodic structure 2 is formed on the surface of the substrate 1.
Specifically, a plurality of semiconductor layers 2a and metal layers 2b are alternately stacked by, for example, sputtering. The lowest layer is the semiconductor layer 2a, and an ohmic contact with the substrate 1 is obtained.
The semiconductor layer 2a is selected from an n-type semiconductor having a property of obtaining an ohmic contact with a metal that can be formed relatively easily, for example, n-ZnO doped with an n-type impurity, n-InGaZnO, n-MgZnO, n-InZnO, and the like. One kind. Here, the semiconductor layer 2a is formed to a thickness of, for example, about 10 nm to 1 μm with n-ZnO. As the n-type impurity to be doped, for example, Ga, Al, In, and the like are conceivable. However, ZnO usually formed by sputtering or the like may be n-type related to oxygen defects. A typical n-type impurity doping is unnecessary.

The concentration of the n-type impurity in the semiconductor layer 2a is, for example, about 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ , here about 1 × 10 ¹⁸ / cm ³ . When the concentration is less than 1 × 10 ¹⁷ / cm ³ , the contact resistance cannot be sufficiently reduced with the metal layer 2b. The upper limit of the content concentration is not particularly specified. However, if the concentration is higher than 1 × 10 ²⁰ / cm ³ , the energy level of the semiconductor layer 2a is almost degenerate and the possibility of metallic behavior cannot be denied. For this reason, the upper limit of the content concentration is about 1 × 10 ²⁰ / cm ³ here. By setting the concentration of the n-type impurity in the semiconductor layer 2a to about 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ , the contact resistance with the metal layer 2b is sufficiently reduced.
Similarly, when n-InGaZnO, n-MgZnO, or n-InZnO is used for the semiconductor layer 2a, the concentration of the n-type impurity in the semiconductor layer 2a is, for example, 1 × 10 ¹⁷ / cm ³ to 1 × 10 ^20. / Cm ³ .

The metal layer 2b includes one type selected from metals having the property of obtaining ohmic contact with n-ZnO, for example, Al, Au, Ni and the like. Here, the metal layer 2b is formed of Al with a film thickness of about 10 nm to 1 μm, for example.
The number of layers of the semiconductor layer 2a and the metal layer 2b is not particularly limited, but a temperature difference necessary for generating a thermoelectromotive force between the substrates 1 and 3 shown in FIG. Must be set to That is, the number of layers (distance between the substrates 1 and 3) is individually set according to the application range. FIG. 1B illustrates a case where 20 semiconductor layers 2a and 20 metal layers 2b are formed.
As described above, the periodic structure 2 having a superlattice structure, which is a thermoelectric conversion portion in which a plurality of semiconductor layers 2a and metal layers 2b are alternately stacked, is formed.

Subsequently, as shown in FIG. 1C, a substrate 3 is formed on the periodic structure 2.
Specifically, for example, similarly to the substrate 1, a substrate 3 made of Al and having a thickness of about 100 μm is prepared, and the substrate 3 is formed on the periodic structure 2, that is, on the uppermost metal layer 2 b of the periodic structure 2. . The substrate 3 also functions as the other of the pair of electrodes of the thermoelectric conversion element.
Projecting electrode connection portions made of, for example, Al are formed at predetermined portions of the substrates 1 and 3 and serve as extraction portions for thermoelectrically converted electricity.
As described above, the thermoelectric conversion element according to the present embodiment is formed.

  In the thermoelectric conversion element according to the present embodiment, as shown in FIG. 2, the substrate 1 is a positive low-temperature side electrode, the substrate 3 is a negative high-temperature side electrode, and the heat source 4 is in contact with the substrate 3. A temperature gradient is formed in the vertical direction between the substrate 3 and the substrate 1. Electrons serving as carriers diffuse in the periodic structure 2 from the substrate 3 serving as the negative electrode toward the substrate 1 serving as the positive electrode. Here, the heat source 4 is assumed to be non-conductive. When the heat source is conductive and electrical insulation is necessary, an insulating plate is provided on the substrate 3 so that the heat source contacts the insulating plate.

In the thermoelectric conversion element, the greater the electric conduction and the smaller the heat conduction, the higher the figure of merit ZT and the higher the thermoelectric conversion efficiency.
In this embodiment, ohmic contact is formed at the interface between the semiconductor layer 2a and the metal layer 2b constituting the periodic structure 2 as described above, and no Schottky barrier exists at the interface. Therefore, electrons as carriers diffuse in the periodic structure 2 without being blocked at the interface. Thereby, big electric conduction is obtained.
In this embodiment, since the periodic structure 2 is configured by laminating a plurality of semiconductor layers 2a and metal layers 2b, there are many interfaces between the semiconductor layers 2a and the metal layers 2b. Since phonons are scattered at each interface, heat scattering is more likely to occur as the number of interfaces increases in the thermoelectric conversion portion disposed between the electrodes. Therefore, due to the existence of a large number of interfaces in the periodic structure 2, the heat transferred from the heat source 4 is greatly scattered by the periodic structure 2. Thereby, thermal conductivity falls.
As described above, in the thermoelectric conversion element according to the present embodiment, although large electrical conduction is obtained, the thermal conductivity is small, and extremely high thermoelectric conversion efficiency is realized.

  As described above, according to the present embodiment, it is possible to realize a thermoelectric conversion element with a relatively simple configuration and extremely high conversion efficiency that has been difficult to realize with a conventional single semiconductor layer.

(Modification)
In this example, the configuration of the thermoelectric conversion element having the periodic structure 2 is disclosed together with the manufacturing method as in the first embodiment, but the first embodiment is different from the first embodiment in that a substrate is used separately from the electrode. Is different.
FIGS. 3A and 3B are schematic views illustrating a method of manufacturing a thermoelectric conversion element according to a modification of the first embodiment in the order of steps, in which FIGS. 3A and 3B are cross-sectional views and FIG. 3C is a perspective view.

First, as shown in FIG. 3A, a substrate 11 is prepared.
The substrate 11 is used as a substrate for forming the periodic structure 2. As the material, for example, Al or Cu is used. Here, the substrate 11 is made of, for example, Al and has a thickness of about 100 μm.

Subsequently, as illustrated in FIG. 3B, the periodic structure 2 is formed on the surface of the substrate 11.
Specifically, a plurality of semiconductor layers 2b and metal layers 2a are alternately stacked by, for example, sputtering. Similar to the first embodiment, the semiconductor layer 2a is an n-type semiconductor having a property of obtaining ohmic contact with a metal that can be formed relatively easily, for example, n-ZnO doped with an n-type impurity, n-InGaZnO, n -1 type chosen from MgZnO, n-InZnO, etc. is included. Here, the semiconductor layer 2a is formed to a thickness of, for example, about 10 nm to 1 μm with n-ZnO. As the n-type impurity to be doped, for example, Ga, Al, In, and the like are conceivable. However, ZnO usually formed by sputtering or the like may be an n-type related to oxygen defects, and in that case, Intentional n-type impurity doping is not required. The metal layer 2b is made of Al and has a thickness of about 10 nm to 1 μm. Since the lowermost layer of the periodic structure 2 is the metal layer 2b and is the same material as the substrate 11, there is no problem of contact resistance. FIG. 3B illustrates a case where, unlike FIG. 1, four metal layers 2b and three semiconductor layers 2a are formed.
As described above, the periodic structure 2 having a superlattice structure, which is a thermoelectric conversion portion in which a plurality of metal layers 2b and semiconductor layers 2a are alternately stacked, is formed.

Subsequently, as shown in FIG. 3C, a pair of electrodes 12 and 13 are formed.
Specifically, an electrode metal is deposited on the periodic structure 2, that is, on the uppermost metal layer 2 b of the periodic structure 2 by, for example, an evaporation method. The electrode metal is Ti / Au, AuGe / Au, etc., here Ti / Au is used, for example, deposited to a film thickness of about 100 nm / 500 nm. Thereby, the electrode 12 is formed.
Similarly, an electrode metal, here Ti / Au, is deposited to a thickness of, for example, about 100 nm / 500 nm on the back surface of the substrate 11 by, for example, vapor deposition. Thereby, the electrode 13 is formed.
Electrode connection portions serving as thermoelectrically converted electricity extraction portions are formed at predetermined portions of the electrodes 12 and 13.
As described above, the thermoelectric conversion element according to the present embodiment is formed.

  As described above, according to this example, as in the first embodiment, the thermoelectric conversion element having a relatively simple configuration and extremely high conversion efficiency that was difficult to realize with a conventional single semiconductor layer. Can be realized.

(Second Embodiment)
In the present embodiment, the configuration of a thermoelectric conversion element having one periodic structure as in the first embodiment is disclosed together with the manufacturing method thereof, but the first is that the semiconductor layer of the periodic structure is a p-type semiconductor. This is different from the first embodiment.
FIG. 4 is a schematic cross-sectional view illustrating the method of manufacturing the thermoelectric conversion element according to the second embodiment in the order of steps. FIG. 5 is a schematic cross-sectional view showing a thermoelectric conversion element and a heat source according to the second embodiment.

  First, as shown in FIG. 4A, as in FIG. 1A of the first embodiment, a substrate 1 made of, for example, Ni that also functions as one of a pair of electrodes is prepared.

Subsequently, as shown in FIG. 4B, a periodic structure 21 is formed on the surface of the substrate 1.
Specifically, a plurality of semiconductor layers 21a and metal layers 21b are alternately stacked by, for example, sputtering. The lowermost layer is the semiconductor layer 21a, and an ohmic contact with the substrate 1 is obtained.
The semiconductor layer 21a includes a p-type semiconductor having a property of obtaining ohmic contact with a metal that can be formed relatively easily, for example, n-InZnO doped with a p-type impurity, p-MgZnO, or the like. Here, the semiconductor layer 21a is formed to a thickness of about 10 nm to 1 μm by p-ZnO, for example. Examples of the p-type impurity to be doped include N and P. Here, for example, P is used.

The concentration of the p-type impurity in the semiconductor layer 21a is, for example, about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²⁰ / cm ³ , as in the semiconductor layer 2a in the first embodiment, here 1 × 10 ¹⁷ / It is about cm ³ .
Similarly, when p-MgZnO is used for the semiconductor layer 21a, the concentration of the n-type impurity in the semiconductor layer 21a is, for example, about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²⁰ / cm ³ .

The metal layer 21b includes one kind selected from metals having a property of obtaining ohmic contact with p-InGaZnO, such as Au and Ni. Here, the metal layer 21b is formed with a thickness of, for example, about 10 nm to 1 μm using Ni.
The number of layers of the semiconductor layer 21a and the metal layer 21b is not particularly limited, but a temperature difference necessary for generating a thermoelectromotive force between the substrates 1 and 3 shown in FIG. Must be set to That is, the number of layers (distance between the substrates 1 and 3) is individually set according to the application range. FIG. 4B illustrates a case where 20 semiconductor layers 21a and 20 metal layers 21b are formed.
As described above, the periodic structure 21 having a superlattice structure, which is a thermoelectric conversion portion in which a plurality of semiconductor layers 21a and metal layers 21b are alternately stacked, is formed.

Subsequently, as shown in FIG. 4C, as in FIG. 1C of the first embodiment, on the periodic structure 21, that is, on the uppermost metal layer 21b of the periodic structure 21, for example, A substrate 3 made of Al is pasted.
Projecting electrode connection portions made of, for example, Al are formed at predetermined portions of the substrates 1 and 3 and serve as extraction portions for thermoelectrically converted electricity.
As described above, the thermoelectric conversion element according to the present embodiment is formed.

  In the thermoelectric conversion element according to the present embodiment, as shown in FIG. 5, the substrate 1 is a negative low temperature side electrode, the substrate 3 is a positive high temperature side electrode, and the heat source 4 is disposed on the substrate 3. The holes (carriers) that are carriers are diffused in the periodic structure 21 from the substrate 3 that is the positive electrode toward the substrate 1 that is the negative electrode. Here, the heat source 4 is assumed to be non-conductive. When the heat source is conductive and electrical insulation is necessary, an insulating plate is provided on the substrate 3 so that the heat source contacts the insulating plate.

In the thermoelectric conversion element, the greater the electric conduction and the smaller the heat conduction, the higher the figure of merit ZT and the higher the thermoelectric conversion efficiency.
In the present embodiment, ohmic contact is formed at the interface between the semiconductor layer 21a and the metal layer 21b constituting the periodic structure 21 as described above, and no Schottky barrier exists at the interface. Therefore, holes serving as carriers diffuse in the periodic structure 21 without being blocked at the interface. Thereby, big electric conduction is obtained.
In the present embodiment, since the periodic structure 21 is configured by laminating a plurality of semiconductor layers 21a and metal layers 21b, there are many interfaces between the semiconductor layers 21a and the metal layers 21b. Since phonons are scattered at each interface, heat scattering is more likely to occur as the number of interfaces increases in the thermoelectric conversion portion disposed between the electrodes. Therefore, due to the existence of a large number of interfaces in the periodic structure 21, the heat transferred from the heat source 4 is greatly scattered by the periodic structure 21. Thereby, thermal conductivity falls.
As described above, in the thermoelectric conversion element according to the present embodiment, although large electrical conduction is obtained, the thermal conductivity is small, and extremely high thermoelectric conversion efficiency is realized.

  As described above, according to the present embodiment, it is possible to realize a thermoelectric conversion element with a relatively simple configuration and extremely high conversion efficiency that has been difficult to realize with a conventional single semiconductor layer.

(Modification)
In this example, the configuration of the thermoelectric conversion element having one periodic structure as in the second embodiment is disclosed together with the manufacturing method thereof, but the second embodiment is used in that the substrate is used separately from the electrode. Is different.
FIGS. 6A and 6B are schematic views illustrating a method of manufacturing a thermoelectric conversion element according to a modification of the second embodiment in the order of steps, in which FIGS. 6A and 6B are cross-sectional views and FIG.

  First, as shown in FIG. 6A, as in FIG. 3A of the first embodiment, a substrate 11 made of, for example, Ni for forming the periodic structure 21 is prepared.

Subsequently, as shown in FIG. 6B, the periodic structure 21 is formed on the surface of the substrate 11.
Specifically, a plurality of metal layers 21b and semiconductor layers 21a are alternately stacked by, for example, sputtering. As in the first embodiment, the semiconductor layer 21a is formed to a thickness of about 10 nm to 1 μm with p-ZnO doped with, for example, P, which is a p-type impurity, to a concentration of about 1 × 10 ¹⁷ / cm ^3. The layer 21b is formed of Ni to a thickness of about 10 nm to 1 μm. Since the lowermost layer of the periodic structure 21 is the metal layer 21b, which is the same material as the substrate 11, there is no problem of contact resistance. FIG. 6B illustrates a case where four metal layers 21b and three semiconductor layers 21a are formed.
As described above, the periodic structure 21 having a superlattice structure, which is a thermoelectric conversion portion in which a plurality of metal layers 21b and semiconductor layers 21a are alternately stacked, is formed.

Subsequently, as shown in FIG. 6C, as in FIG. 3C of the first embodiment, on the periodic structure 21, that is, on the uppermost metal layer 21b of the periodic structure 21, for example, An electrode 12 made of Ti / Au is formed. Similarly, an electrode 13 made of, for example, Ti / Au is formed on the back surface of the substrate 11.
Electrode connection portions serving as thermoelectrically converted electricity extraction portions are formed at predetermined portions of the electrodes 12 and 13.
As described above, the thermoelectric conversion element according to the present embodiment is formed.

  As described above, according to the present embodiment, as in the first embodiment, a thermoelectric conversion with a relatively simple configuration and extremely high conversion efficiency that was difficult to achieve with a conventional single semiconductor layer. An element can be realized.

(Third embodiment)
In the present embodiment, the periodic structure in the first embodiment is processed into a plurality of columnar bodies, and the configuration of the thermoelectric conversion element in which these columnar bodies are arranged in parallel is disclosed together with the manufacturing method thereof.
FIG. 7 is a schematic cross-sectional view showing a thermoelectric conversion element and a heat source according to the third embodiment.

  In order to manufacture a thermoelectric conversion element, first, similarly to FIGS. 1A and 1B of the first embodiment, an n-type semiconductor layer 2a and a metal layer 2b are formed on a substrate 1 made of Al. A plurality of layers are alternately stacked.

Subsequently, the stacked body of the n-type semiconductor layer 2a and the metal layer 2b is processed so as to be divided into a plurality of pieces in the vertical direction by lithography, ion milling using Ar gas, or the like. Here, the laminated body is processed into a plurality of desired columnar bodies (a shape whose height is larger than one side of a rectangular cross section). As the desired columnar shape, as will be described later, the laminated body is processed into a lattice shape in the longitudinal direction, and the shape of standing in a matrix on the substrate 1 or the laminated body is processed into a strip shape in the longitudinal direction. However, the shape etc. which parallel on the wall shape on the board | substrate 1 can be considered. Here, the former shape is used. As described above, a columnar body in which a plurality of semiconductor layers 2a and metal layers 2b are alternately stacked, and a wire-like periodic structure 2A standing in a matrix on the substrate 1 is formed. The length of one side of the rectangular cross section of the wire-like periodic structure 2A is, for example, 1 μm or less, and the cross-sectional area is, for example, 1 μm ² or less. The periodic structure of the present embodiment is configured from the plurality of wire-like periodic structures 2A.

Subsequently, as in FIG. 1C of the first embodiment, the substrate 3 made of Al is pasted on the plurality of wire-like periodic structures 2A.
As described above, the thermoelectric conversion element according to the present embodiment is formed.

  In the thermoelectric conversion element according to the present embodiment, as shown in FIG. 7, the substrate 1 is a positive low-temperature side electrode, the substrate 3 is a negative high-temperature side electrode, and the heat source 4 is in contact with the substrate 3. Electrons as carriers diffuse from the substrate 3 as a negative electrode toward the substrate 1 as a positive electrode in each wire-like periodic structure 2A. Here, the heat source 4 is assumed to be non-conductive. When the heat source is conductive, an insulating plate is provided on the substrate 3 so that the heat source contacts the insulating plate.

In the thermoelectric conversion element of the present embodiment, as in the first embodiment, a plurality of conductor layers 2a and metal layers 2b are laminated to form each wire-like periodic structure 2A. Therefore, the semiconductor layer 2a and the metal layer 2b There are many interfaces. Therefore, due to the existence of a large number of the interfaces in each wire-like periodic structure 2A, the heat transferred from the heat source 4 is greatly scattered by each wire-like periodic structure 2A. Thereby, thermal conductivity falls.
Furthermore, in the thermoelectric conversion element of this embodiment, since the periodic structure 2 of the first embodiment is processed into a large number of wire-like periodic structures 2A, the surface area of the entire plurality of wire-like periodic structures 2A is large. growing. That is, in each wire-like periodic structure 2A, in addition to the interface between the semiconductor layer 2a and the metal layer 2b, the heat transmitted from the heat generating source 4 is greatly scattered by the surface.
As described above, in the thermoelectric conversion element according to the present embodiment, although large electric conduction is obtained, the thermal conductivity is small, and higher thermoelectric conversion efficiency is realized.

  As described above, according to the present embodiment, it is possible to realize a thermoelectric conversion element with a relatively simple configuration and extremely high conversion efficiency that has been difficult to realize with a conventional single semiconductor layer.

(Modification)
In this example, the configuration of a thermoelectric conversion element having a plurality of wire-like periodic structures 2A as in the third embodiment is disclosed together with its manufacturing method, but the first is that a substrate is used separately from the electrodes. This is different from the embodiment.
FIG. 8 is a schematic perspective view illustrating a method of manufacturing a thermoelectric conversion element according to a modification of the third embodiment in the order of steps.

  First, similarly to FIGS. 3A and 3B of the first embodiment, a plurality of metal layers 2b and semiconductor layers 2a are alternately stacked on a substrate 11 made of Al or Cu. Here, unlike FIG. 7, a case where four metal layers 2b and three semiconductor layers 2a are formed is illustrated.

Subsequently, a pair of electrodes 12 and 13 is formed as in FIG. 3C of the first embodiment.
Specifically, the electrode 12 is formed on the uppermost metal layer 2 b of the periodic structure 2, and the electrode 13 is formed on the back surface of the substrate 11.

Then, as shown to Fig.8 (a), the laminated body of the semiconductor layer 2a and the metal layer 2b, and the electrode 12 is divided | segmented into multiple pieces longitudinally, and several wire-like periodic structure 2A is formed.
Specifically, the stacked body of the semiconductor layer 2a and the metal layer 2b and the electrode 12 is processed into a lattice shape in the vertical direction by lithography, ion milling using Ar gas, or the like. As a result, a plurality of columnar wire-like periodic structures 2 </ b> A having the electrodes 12 </ b> A on the uppermost surface and standing in a matrix on the substrate 11 are formed.

Here, instead of forming a plurality of wire-like periodic structures 2A, a plurality of strip-like periodic structures 2B may be formed as shown in FIG. 8B.
In this case, the stacked body of the semiconductor layer 2a and the metal layer 2b and the electrode 12 is processed into a strip shape in the vertical direction by lithography, ion milling using Ar gas, or the like. As a result, a plurality of wall-like strip-shaped periodic structures 2B having the electrode 12B on the uppermost surface and arranged in parallel on the substrate 11 are formed.

Electrode connection portions serving as thermoelectrically converted electricity extraction portions are formed at predetermined portions of the electrodes 12 and 13.
As described above, the thermoelectric conversion element according to the present embodiment is formed.

  As described above, according to this example, as in the first embodiment, the thermoelectric conversion element having a relatively simple configuration and extremely high conversion efficiency that was difficult to realize with a conventional single semiconductor layer. Can be realized.

  In addition, the periodic structure body in 2nd Embodiment may be processed into a some columnar body similarly to this embodiment, and the thermoelectric conversion element which these columnar bodies parallel may be formed. In this case, each columnar body is formed by alternately stacking a plurality of p-type semiconductor layers 21a and metal layers 21b.

(Fourth embodiment)
In the present embodiment, a thermoelectric conversion element using both the periodic structures 2 and 21 according to the first and second embodiments is disclosed.
FIG. 9 is a cross-sectional view illustrating a schematic configuration of the thermoelectric conversion element according to the fourth embodiment.

This thermoelectric conversion element is configured such that electrode-connected periodic structures 2 and 21 are alternately arranged in parallel between a pair of substrates 31 and 32 that are arranged with their surfaces facing each other.
The substrates 31 and 32 are made of an insulating material, here polyimide.
In the present embodiment, since the substrate 32 is provided, even if the heat source is conductive, the thermoelectric conversion element is not affected. The heat source may be conductive or non-conductive, but is mainly considered to be conductive.
Moreover, in this embodiment, even if the part of the predetermined member which contact | connects the lower surface of a thermoelectric conversion element is electroconductive, it does not affect a thermoelectric conversion element. The part of the predetermined member may be conductive or non-conductive, but is mainly considered to be conductive.

A plurality of electrodes 33 are arranged in parallel on the substrates 31 and 32. Projecting electrode connecting portions 33a and 33b made of, for example, Al are formed on the left and right electrodes 33 in FIG.
The electrode 33 is not particularly limited, but for example, Al or Cu is used. Here, the electrode 33 is made of, for example, Al and has a thickness of about 1 μm.

In FIG. 9, the periodic structure 2 having an n-type semiconductor layer according to the first embodiment is connected between the upper and lower electrodes 33 via a metal layer 34a. For the metal layer 34a, a metal capable of obtaining ohmic contact with the n-type semiconductor layer constituting the periodic structure 2, such as Al, is used, and the thickness thereof is, for example, 10 nm to 1 μm. Further, the periodic structure 21 having the p-type semiconductor layer according to the second embodiment is connected between the upper and lower electrodes 33 via the metal layer 34b. The metal layer 34b is made of a metal that can make ohmic contact with the p-type semiconductor layer constituting the periodic structure 21, such as Ni, and has a thickness of 10 nm to 1 μm, for example.
The periodic structures 2 and 21 are formed by the same method as in the first and second embodiments.

In the thermoelectric conversion element according to the present embodiment, the heat source contacts the substrate 32, that is, the substrate 32 is on the high temperature side and the substrate 31 is on the low temperature side.
In the periodic structure 2, electrons as carriers diffuse in the periodic structure 2 from the substrate 32 side toward the substrate 31 side.
In the periodic structure 21, holes serving as carriers diffuse in the periodic structure 21 from the substrate 32 side toward the substrate 31 side.
Therefore, in this thermoelectric conversion element, a passage for carriers (electrons and holes) that meanders alternately through the periodic structures 2 and 21 from the electrode connection portion 33a to the electrode connection portion 33b is formed. The connection part 33a becomes a high potential with respect to the electrode connection part 33b.

  As described above, according to the present embodiment, it is possible to realize a thermoelectric conversion element with a relatively simple configuration and extremely high conversion efficiency that has been difficult to realize with a conventional single semiconductor layer. In the present embodiment, both electrode connection portions 33a and 33b serving as thermoelectrically converted electricity extraction portions are formed on one substrate side, here, on the substrate 31 side on the low temperature side. There is no.

  Here, in the thermoelectric conversion element according to the present embodiment, various configurations according to the material (conductive or non-conductive) of the heat source that contacts the high temperature side and the portion of the predetermined member that contacts the low temperature side are disclosed.

1. When the heat source is non-conductive (1)
As shown in FIG. 10, the substrate 32 may not be formed. In this case, the heat generation source comes into contact with the upper electrode 33. However, since the heat generation source is non-conductive, there is no concern about the influence on the thermoelectric conversion element.
In this case, an insulating substrate 31 is provided below the lower electrode 33, and a portion of the predetermined member is in contact with the substrate 31. Therefore, there is no problem whether the predetermined member portion is conductive or non-conductive.

2. When the heat source is non-conductive (2)
As shown in FIG. 11, an opening 35 a that exposes a part of the surface of the upper electrode 33 is formed in the substrate 32. The opening 35 a is filled with a conductive material, and an electrode 35 b electrically connected to the upper electrode 33 is formed by plating or the like so as to slightly protrude upward from the surface of the substrate 32. In this case, the heat source comes into contact with the electrode 35. However, since the heat source is non-conductive, there is no concern about the influence on the thermoelectric conversion element.
In this case, an insulating substrate 31 is provided below the lower electrode 33, and a portion of the predetermined member is in contact with the substrate 31. Therefore, there is no problem whether the predetermined member portion is conductive or non-conductive.

3. When the part of the predetermined member is non-conductive (1)
As shown in FIG. 12, the insulating substrate 31 under the lower electrode 33 may not be formed. In this case, the portion of the predetermined member comes into contact with the lower electrode 33, but since the portion is non-conductive, there is no concern about the influence on the thermoelectric conversion element.
In this case, the upper electrode 33 is provided with an insulating substrate 32, and the heat source contacts the substrate 32. Therefore, there is no problem whether the heat source is conductive or non-conductive.

4). When the part of the predetermined member is non-conductive (2)
As shown in FIG. 13, an opening 36 a that exposes a part of the surface of the lower electrode 33 is formed in the substrate 31. The opening 36 a is filled with a conductive material, and an electrode 36 b electrically connected to the lower electrode 33 is formed by plating or the like so as to slightly protrude downward from the back surface of the substrate 31. In this case, the heat source comes into contact with the electrode 36b. However, since the heat source is non-conductive, there is no concern about the influence on the thermoelectric conversion element.
In this case, an insulating substrate 32 is provided on the upper electrode 33, and the heat generation source contacts the substrate 32. Therefore, there is no problem whether the heat source is conductive or non-conductive.

5. When both the heat source and the predetermined member are non-conductive, as shown in FIG. 14, an opening 35 a that exposes a part of the surface of the upper electrode 33 is formed in the substrate 32. The opening 35 a is filled with a conductive material, and an electrode 35 b electrically connected to the upper electrode 33 is formed by plating or the like so as to slightly protrude upward from the surface of the substrate 32. In this case, the heat generation source comes into contact with the electrode 35b. However, since the heat generation source is non-conductive, there is no concern about the influence on the thermoelectric conversion element.
Further, an opening 36 a that exposes a part of the surface of the lower electrode 33 is formed in the substrate 31. The opening 36 a is filled with a conductive material, and an electrode 36 b electrically connected to the lower electrode 33 is formed by plating or the like so as to slightly protrude downward from the back surface of the substrate 31. In this case, the heat source comes into contact with the electrode 36b. However, since the heat source is non-conductive, there is no concern about the influence on the thermoelectric conversion element.

(Modification)
In this example, as in the fourth embodiment, a thermoelectric conversion element using a plurality of periodic structures is disclosed, but the periodic structure 2 using an n-type semiconductor layer according to the first embodiment, The fourth embodiment is different from the fourth embodiment in that it is a thermoelectric conversion element in which a plurality of single p-type semiconductor layers are alternately arranged.
FIG. 15: is sectional drawing which shows schematic structure of the thermoelectric conversion element by the modification of 4th Embodiment.

This thermoelectric conversion element is configured such that the electrode-connected periodic structure 2 and the single p-type semiconductor layer 37 are alternately arranged between a pair of substrates 31 and 32 arranged to face each other.
Similar to the third embodiment, the lower electrode 33 is arranged in parallel on the substrate 31. Electrode connection portions 33 a and 33 b are formed at both left and right ends of the lower electrode 33. Under the substrate 32, an upper electrode 33 is arranged in parallel.

  In FIG. 15, the periodic structure 2 having an n-type semiconductor layer according to the first embodiment is connected between the upper and lower electrodes 33 via a metal layer 34a. For the metal layer 34a, a metal capable of obtaining ohmic contact with the n-type semiconductor layer constituting the periodic structure 2, such as Al, is used, and the thickness thereof is, for example, 10 nm to 1 μm. Furthermore, a single p-type semiconductor layer 37 is connected between the upper and lower electrodes 33 via a metal layer 34b. For the p-type semiconductor layer 37, for example, sintered SiGe is used. The metal layer 34b is a metal capable of obtaining ohmic contact with the p-type semiconductor layer 37, in this case, for example, Al, and the thickness thereof is, for example, 10 nm to 1 μm.

  As described above, according to this example, it is possible to realize a thermoelectric conversion element with a comparatively simple configuration and extremely high conversion efficiency that has been difficult to achieve with only a single conventional semiconductor layer. In the present embodiment, both electrode connection portions 33a and 33b serving as thermoelectrically converted electricity extraction portions are formed on one substrate side, here, on the substrate 31 side on the low temperature side. There is no.

  Instead of the modification of the fourth embodiment, a plurality of conventional single n-type semiconductor layers and periodic structures 21 using the p-type semiconductor layers according to the second embodiment are alternately arranged. It is also conceivable to construct a thermoelectric conversion element.

  Further, instead of using both the periodic structures 2 and 21 according to the first and second embodiments, a thermoelectric conversion element may be formed as in the present embodiment using the third embodiment. For example, a plurality of wire-like periodic structures 2A obtained by alternately laminating a plurality of n-type semiconductor layers 2a and metal layers 2b, and a plurality of p-type semiconductor layers 21a and metal layers 21b are alternately laminated. A thermoelectric conversion element is configured as shown in FIG. 9 using a plurality of columnar bodies.

(Fifth embodiment)
In this embodiment, an electronic device including an LSI element such as a CPU is illustrated.
FIG. 16 is a cross-sectional view illustrating a schematic configuration of an electronic device according to the fifth embodiment.

  This electronic device includes a CPU 44, a thermoelectric conversion mechanism 45 connected to the CPU 44, and a power storage mechanism 46 above the printed wiring board 41. A buildup substrate 43 is connected to the printed wiring board 41 by solder bumps 42 a, and a CPU 44, a thermoelectric conversion mechanism 45, and a power storage mechanism 46 are provided on the buildup substrate 43.

The CPU 44 is connected to the build-up substrate 43 by solder bumps 42b, and is a heat source of the electronic device due to its operation.
The thermoelectric conversion mechanism 45 includes radiators 51 and 52 and a thermoelectric conversion element 53.
The radiator 51 has a water-cooled pipe inside, and is arranged so as to hang over the build-up board 43 from the CPU 44. The radiator 52 is disposed on the thermoelectric conversion element 53.
The thermoelectric conversion element 53 is a thermoelectric conversion element according to the above-described first, second, third, or fourth embodiment, or a modified example thereof, and the high temperature side thereof is disposed on the radiator 51.
The power storage mechanism 46 is a storage battery or the like, and is connected to the thermoelectric conversion element 53.

  Heat generated by the CPU 44 that is a heat source is transmitted to the thermoelectric conversion element 53 via the radiator 51. As described above, the thermoelectric conversion element 53 performs thermoelectric conversion with high conversion efficiency, and the converted electricity is stored in the power storage mechanism 46.

According to the present embodiment, the thermoelectric conversion element according to the first, second, third, or fourth embodiment or a modification thereof is arranged as the thermoelectric conversion element 53 in the electronic device. Accordingly, thermoelectric conversion with extremely high conversion efficiency, which has been difficult to realize with a conventional single semiconductor layer, is possible with a relatively simple configuration, and waste heat energy can be used efficiently with high efficiency.
Note that the target on which the first or second, second, third, or fourth embodiment, or the thermoelectric conversion element according to the modification is mounted is not limited to the electronic apparatus according to the present embodiment. For example, not only thermoelectric conversion using a heat source of an electronic device such as a high output / high frequency power amplifier, a drive module of an electric vehicle, but also all devices that can be used for waste heat, such as a thermal power plant, a server system, a thermometer, and the like Applicable to the system.

  Hereinafter, various aspects of the thermoelectric conversion element and the electronic device are collectively described as additional notes.

(Supplementary note 1) a periodic structure in which metal layers and semiconductor layers are alternately stacked;
A thermoelectric conversion element comprising: a pair of electrode layers formed above and below the periodic structure.

  (Supplementary Note 2) The thermoelectric conversion element according to Supplementary Note 1, wherein the periodic structure includes a plurality of columnar bodies in which the metal layers and the semiconductor layers are alternately stacked in parallel between the electrode layers. .

  (Supplementary note 3) The thermoelectric conversion element according to supplementary note 1 or 2, wherein in the periodic structure, the metal layer and the semiconductor layer are in ohmic contact.

(Additional remark 4) The said semiconductor layer contains an n-type impurity in the density | concentration of 1 * 10 < ¹⁷ > / cm < ³ > or more, The thermoelectric conversion element of any one of Additional remark 1-3 characterized by the above-mentioned.

(Appendix 5) The semiconductor layer contains an n-type impurity,
Any one of appendices 1 to 4, wherein the metal layer has one selected from Al, Au, and Ni, and the semiconductor layer has one selected from ZnO, InGaZnO, MgZnO, and InZnO. The thermoelectric conversion element according to Item 1.

(Appendix 6) The thermoelectric conversion element according to any one of appendices 1 to 3, wherein the semiconductor layer contains a p-type impurity at a concentration of 1 × 10 ¹⁶ / cm ³ or more.

(Appendix 7) The semiconductor layer contains a p-type impurity,
The thermoelectric conversion element according to any one of appendices 1 to 3 and 6, wherein the metal layer has Ni and the semiconductor layer has one selected from ZnO and MgZnO.

(Appendix 8) Steps of alternately laminating metal layers and semiconductor layers to form a periodic structure;
Forming a pair of electrode layers above and below the periodic structure. A method of manufacturing a thermoelectric conversion element, comprising:

(Appendix 9) Before forming the electrode layer,
The manufacturing of the thermoelectric conversion element according to appendix 8, further comprising a step of processing the periodic structure so that a plurality of columnar bodies in which the metal layers and the semiconductor layers are alternately stacked are arranged in parallel. Method.

(Additional remark 10) The electronic component used as a heat generation source,
An electronic apparatus comprising: the thermoelectric conversion element according to any one of appendices 1 to 7, which converts heat generated from the electronic component into electricity.

1, 3, 11, 31, 32 Substrate 2, 21 Periodic structure 2a, 21a Semiconductor layer 2A Wire-like periodic structure 2B Strip-like periodic structure 2b, 21b Metal layer 4 Heat source 12, 13, 33, 35b, 36b Electrodes 33a, 33b Electrode connecting portions 34a, 34b Metal layers 35a, 36a Openings 37 P-type semiconductor layer 41 Printed wiring boards 42a, 42b Solder bumps 43 Build-up board 44 CPU
45 Thermoelectric conversion mechanism 46 Power storage mechanism 51, 52 Radiator 53 Thermoelectric conversion element

Claims (7)

A periodic structure in which metal layers and semiconductor layers are alternately stacked;
A thermoelectric conversion element comprising: a pair of electrode layers formed above and below the periodic structure.   2. The thermoelectric conversion element according to claim 1, wherein the periodic structure is composed of a plurality of columnar bodies in which the metal layers and the semiconductor layers are alternately stacked in parallel between the electrode layers.   The thermoelectric conversion element according to claim 1, wherein in the periodic structure, the metal layer and the semiconductor layer are in ohmic contact. The semiconductor layer contains an n-type impurity;
4. The metal layer according to claim 1, wherein the metal layer has one kind selected from Al, Au, and Ni, and the semiconductor layer has one kind selected from ZnO, InGaZnO, MgZnO, and InZnO. The thermoelectric conversion element of Claim 1. Forming a periodic structure by alternately laminating metal layers and semiconductor layers;
Forming a pair of electrode layers above and below the periodic structure. A method of manufacturing a thermoelectric conversion element, comprising: Before forming the electrode layer,
The thermoelectric conversion element according to claim 5, further comprising a step of processing the periodic structure so that a plurality of columnar bodies in which the metal layers and the semiconductor layers are alternately stacked are arranged in parallel. Production method. An electronic component as a heat source;
An electronic apparatus comprising: the thermoelectric conversion element according to any one of claims 1 to 4 that converts heat generated from the electronic component into electricity.

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