JP5176606B2 - Thermoelectric device element - Google Patents

Description

  The present invention relates to a thermoelectric device element that performs direct conversion from thermal energy to electrical energy.

Thermoelectric power generation is a technology that directly converts thermal energy into electrical energy using the Seebeck effect in which an electromotive force is generated in proportion to the temperature difference applied to both ends of a substance. This technology has been put to practical use in remote power supplies, space power supplies, military power supplies, and the like. A conventional thermoelectric power generation device element has a so-called π-type structure in which a p-type semiconductor and an n-type semiconductor having different carrier signs are combined and connected in parallel and electrically in series. .

The performance of the thermoelectric conversion material used for the thermoelectric conversion device is often evaluated by the figure of merit Z or the figure of merit ZT made dimensionless by applying an absolute temperature.

ZT is a quantity described as Z T = S ² T / ρκ, using S = Seebeck coefficient of the material, ρ = electrical resistivity, κ = thermal conductivity. On the other hand, S ² / ρ taking into account only the Seebeck coefficient S and the electrical resistivity ρ is called a power factor, and is a standard for determining the quality of the power generation performance of the thermoelectric material when the temperature difference is constant.

Bi ₂ Te ₃ currently in practical use as a thermoelectric conversion material has a ZT of about 1 and a power factor of 40 to 50 μW / cmK ² , and has relatively high characteristics at present. In the case of a device configuration, the power generation performance is not so high, and it is not practical enough for more applications.

  On the other hand, as a device configuration other than the π-type, a device configuration utilizing the anisotropy of thermoelectric properties in a natural or artificial laminated structure has been proposed for a long time (see Non-Patent Document 1).

  However, according to Non-Patent Document 1, since such a device does not show improvement in ZT, it is not intended to be used for thermoelectric power generation, but is mainly developed for applications such as infrared sensors. ing.

Further, as a material having a similar structure, there is a thermoelectric conversion material in which an FeSi ₂ -based thermoelectric material and an insulating material such as SiO ₂ having a thickness of 100 nm or less are alternately arranged in a stripe pattern on a substrate. Is disclosed.

According to Patent Document 1, the thermoelectric material having such a fine structure has an improved insulating effect although the Seebeck coefficient is improved by the effect of the fine structure as compared with the single characteristics of the FeSi ₂ -based material which is the main constituent material. Conductivity decreases due to the inclusion of substances. That is, since the electrical resistivity ρ increases, the internal resistance of the thermoelectric device element increases, and as a result, the electric power that can be taken out through the load decreases.

In addition, as a thermoelectric material having a laminated structure, Patent Document 2 discloses a thermoelectric material including a layered body made of a semimetal, a metal, or a synthetic resin. This applies to a conventional so-called π-type device configuration in which a temperature difference is applied in the laminating direction of the layered body and power is taken out via electrodes arranged so as to face each other in the same direction. Essentially, this is different from the device configuration disclosed in Non-Patent Document 1.
JP-A-6-310766 International Publication No. 00/076006 Pamphlet THERMOELECTRICS HANDBOOK, Chapter 45, CRC Press (2006)

As described above, the conventional thermoelectric device cannot obtain sufficient power generation performance sufficient for practical use in more applications. Since the present inventors have practical thermoelectric devices realized with performance results that have extensive studies on device configuration having a laminate, the laminate consisting of metal and SrTiO _3, the opposing direction of the layer direction electrode In comparison with SrTiO ₃ alone, an unexpected finding that the electrical resistivity is suppressed and the power generation characteristics are greatly improved is found in the device tilted with respect to this, and the present invention of the device has been reached based on this finding. It was.

In order to solve the above-described conventional problems, the thermoelectric power generation device element of the present invention includes a first electrode and a second electrode, and a laminated body in which SrTiO ₃ and a metal are alternately laminated. It is electrically connected so that the direction of the layer of the laminated body is inclined with respect to the opposing direction of the second electrode, and is arranged to apply a temperature difference in a direction perpendicular to the opposing direction of the electrode Is done.

According to the thermoelectric device element of the present invention, the thickness ratio of the metal constituting the laminated body and SrTiO ₃ and the inclination angle formed by the direction of the layer of the laminated body and the facing direction of the electrode are appropriately selected. High power generation characteristics that greatly exceed the performance of the material alone can be obtained. As a result, thermoelectric power generation exceeding the conventional performance becomes possible, and a practical thermoelectric power generation device element is realized. That is, it promotes application of energy conversion between heat and electricity, and the industrial value of the present invention is high.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a thermoelectric generator device element according to Embodiment 1 of the present invention.

In FIG. 1, a thermoelectric device element is formed in such a configuration that a laminated body 13 is sandwiched between a first electrode 11 and a second electrode 12 arranged in parallel. The laminated body 13 is configured by alternately laminating SrTiO ₃ layers 14 and metal layers 15, and a direction 16 parallel to the layers is inclined by an angle θ with respect to an opposing direction 17 of the electrodes.

Electron carriers are introduced into the thermoelectric material layer SrTiO ₃ layer constituting the laminate 13, and the number of carriers in that case is preferably about 3 × 10 ²⁰ (cm ⁻³ ). As a method for introducing an electron carrier, strontium constituting the SrTiO ₃ layer is replaced with a stable rare earth element such as lanthanum having a valence of 3+, or titanium is stabilized with a valence of 5+ such as niobium or vanadium. And a method of deliberately depleting oxygen elements and introducing electron carriers into the material.

  A temperature difference is applied when driving the thus configured thermoelectric device element, that is, the direction 18 in which the temperature gradient occurs is orthogonal to the opposing direction 17 of the electrode, and the generated power is the first The electrode 11 and the second electrode 12 are taken out. Specifically, as shown in FIG. 2, the temperature of the thermoelectric device element is set so that the high temperature portion 22 is in close contact with the other surface of the thermoelectric device element 21 and the low temperature portion 23 is in close contact with the other surface. Apply the difference. In this configuration, the direction 24 in which the temperature gradient occurs is perpendicular to the opposing direction of the electrodes as shown in FIG.

In a conventional thermoelectric device element having a π-type structure, it is flat with respect to the direction in which the temperature difference is applied.
An electromotive force is generated only in the row direction, and no electromotive force is generated in the vertical direction. Although the details will be described in Examples described later, the present inventors have examined and optimized various conditions, and thereby, the angle formed between the direction 16 parallel to the layer of the laminated body 13 and the facing direction 17 of the electrode, and SrTiO. _{In the} process of investigating in detail the relationship between the thickness of the _three layers 14 and the metal layer 15 and the ratio thereof and the thermoelectric generation performance, an unexpectedly large heat is generated in the thermoelectric device element of the present invention by appropriately setting the above conditions. It was found that power generation performance can be obtained.

The 1st electrode 11 and the 2nd electrode 12 in the thermoelectric device element of this invention will not be specifically limited if it is a material with good electrical conductivity. Specifically, a metal such as Cu, Ag, Mo, W, Al, Ti, Cr, Au, Pt, or In or a nitride or oxide such as TiN, tin-added indium oxide (ITO), or SnO ₂ is preferable. Also, solder or conductive paste can be used.

  The metal layer 15 constituting the laminate 13 preferably has a high thermal conductivity κ and a low electrical resistivity. Specifically, it is Cu, Ag, Au, Al or an alloy made of these materials, among which Cu, Ag, and Au are preferable, and Cu and Ag are particularly preferable.

  A method for producing the thermoelectric device element of the present invention will be described with reference to FIG.

The laminated structure constituting the laminated body 13 can be produced by, for example, alternately stacking metal 32 foils on which SrTiO ₃ layers 14 are stacked, applying pressure, and further applying heat and pressure forming. . There is no particular limitation on the method for producing the laminate.

  Next, the laminated structure produced as described above is cut out and processed into a plate-like laminated body 13. At this time, as shown by a broken line in FIG. 3, the cutout range 33 is set so that the stacking direction becomes a desired inclination angle with respect to the surface of the plate-shaped stacked body 13. If necessary, the laminated body 13 cut out may be polished. After that, by providing the first electrode 11 and the second electrode 12 on a part or the entire surface of the pair of end surfaces in the inclined direction of the plate-like laminate 13, the thermoelectric device element of the present invention can be obtained. .

The thickness ratio of the metal layer 15 and the SrTiO ₃ layer 14 in the laminate 13 constituting the device is preferably in the range of 99: 1 to 70:30. The reason for this is that, as will be understood from Example 2 described later, the value of the power factor (S ² / ρ) is not sufficiently large if the value is outside this range. The angle θ formed by the direction 16 parallel to the layers of the laminate 13 and the facing direction 17 of the electrodes is preferably in the range of 5 ° to 60 °, and preferably 10 ° to 40 °. Is more preferable. The reason for this is that, as will be understood from Example 1 described later, if the value is less than 5 ° or exceeds 60 °, the value of the power factor (S ² / ρ) does not become sufficiently large.

The method for producing the thin film of the SrTiO ₃ layer 14 using the metal layer 15 as a substrate is not particularly limited, and therefore, by vapor phase growth such as sputtering, vapor deposition, laser ablation, chemical vapor deposition, A method for forming a thin film from a solution by a sol-gel method or a method for polishing and thinning a bulk body can be applied.

  As a method for manufacturing the first electrode 11 and the second electrode 12, various methods such as coating of conductive paste, plating, thermal spraying, and joining by soldering can be used in addition to vapor deposition such as vapor deposition and sputtering. .

(Embodiment 2)
FIG. 4 is a diagram showing the configuration of the thermoelectric generator device according to Embodiment 2 of the present invention.

  In FIG. 4, a plate-like laminate manufactured by the same procedure as that of the first embodiment is electrically connected via a ground electrode 43 and configured in a flat plate shape. By increasing the application area using the thermoelectric power generation device configured as described above, a larger amount of power generation can be obtained as a whole.

The connection electrode 43 in this device is not particularly limited as long as it is a material having good electrical conductivity. Specifically, metals such as Cu, Ag, Mo, W, Al, Ti, Cr, Au, Pt, and In, or nitrides and oxides such as TiN, tin-added indium oxide (ITO), and SnO ₂ are preferable. Also, solder or conductive paste can be used. As a manufacturing method, various methods such as plating and thermal spraying can be used in addition to vapor deposition such as vapor deposition and sputtering.

  When driving a thermoelectric power generation device manufactured in this way, a temperature difference is applied by causing a high temperature part to adhere to one surface of a flat device and a low temperature part to the other surface to generate a heat flow. The electric power converted by the device from the heat flow can be extracted outside through the extraction electrode 44.

  In configuring the thermoelectric power generation device in the present embodiment, the laminates may be electrically connected in parallel as shown in FIG. 5 in addition to being electrically connected in series via the connection electrode 43. The advantage of connecting the stacked bodies in series is to increase the voltage when extracting power.

  When the stacked bodies are connected in parallel, in addition to reducing the internal resistance of the entire thermoelectric power generation device, the electrical connection of the entire device can be maintained even if the electrical connection by the connection electrode 43 is partially broken. There are advantages. That is, by appropriately combining these series and parallel connections (see, for example, FIG. 5), a thermoelectric power generation device having a high power generation capability can be configured.

(Example)
Hereinafter, more specific examples of the present invention will be described.

Example 1
As the SrTiO ₃ layer 14 and the metal laminate 13, several thermoelectric device elements of the present invention were produced using several metal materials. Stack of metal and SrTiO _3, as shown in FIG. 3, bonding with heating by overlapping SrTiO ₃ / metal foil / SrTi O ₃ of sheet obtained by forming a SrTiO ₃ thin film on both surfaces of a metal foil It produced by doing.

For the first electrode 11 and the second electrode 12, Au sandwiched with titanium as an adhesive layer was used. First, an oxide thin film made of a precursor of SrTiO ₃ was formed on both surfaces of a metal foil having a size of 100 mm × 100 mm and a thickness of 95 μm by a sol-gel method. Electron carriers were introduced by replacing strontium with lanthanum. The La-doped SrTiO ₃ precursor is composed of Sr (CH ₃ CO ₂ ) ₂ .1 / 2H ₂ O, Ti (OC ₄ H ₉ ) _4, and La ₂ O ₃ using an atomic ratio. It was weighed and mixed to 98: 0.02: 1 and dissolved with acetic acid / methanol. Further, ethylene glycol was added, and the resulting solution was heated to about 300 ° C. to increase the viscosity, and then applied to a metal foil and dried.

The obtained laminate was cut into a size of 5 mm × 50 mm to obtain strip-shaped pieces. As the metal foil, a foil made of various metal materials such as gold, silver, copper, and aluminum was used. After repeating the same process, 200 pieces of these small pieces were superposed and heated at 500 ° C. for 1 hour under a reduced pressure of 10 ⁻⁴ Pa while applying a load of 100 kg / cm ^{2 in} the stacking direction, and Sr _0.98 La _0.02 At the same time that TiO ₃ was crystallized, each piece was pressed. After crimping, a laminated structure of approximately 5 mm × 50 mm × 20 mm was obtained. The laminated structure was cut and polished to obtain a laminated structure of 3 mm × 48 mm × 20 mm.

When the cross section of the laminate was observed with a scanning electron microscope, it was confirmed that the metal layer was periodically laminated with a thickness of about 95 μm and SrTiO ₃ of about 5 μm. Further, when energy dispersive X-ray elemental analysis was performed on SrTiO ₃ , it was found that a structure was formed with Sr: La: Ti = 0.98: 0.02: 1.

  The laminated structure thus obtained was cut into a flat plate with an inclination of 10 ° intervals as shown in FIG. 3 by cutting using a diamond cutter as shown in FIG. The thickness of the flat plate was 1 mm, and a flat plate having a width of 3 mm and a length of 20 mm was prepared for each inclination angle (θ) in the range from 0 ° to 90 °. Thereafter, an electrode made of titanium-gold using titanium as an adhesive layer was formed on both ends of the long side by sputtering to produce a device having a structure as shown in FIG. The power generation performance was evaluated for the prepared samples.

As shown in FIG. 2, one side of the flat plate device was heated to 150 ° C. with a heater, the other side was cooled to 30 ° C. with water cooling, and the electromotive voltage and electrical resistance between the terminals were measured. In the case of a device tilted 20 ° using silver foil, the electromotive voltage was 135 mV and the resistance was 0.85 mΩ. From this, the power factor was estimated to be 250 μW / cmK ² . When the performance of devices having different inclination angles using each metal material was measured in the same procedure, the results shown in Table 1 were obtained.

From the above results, when the inclination angle is 5 ° to 60 ° almost in common with each metal material, it is possible to obtain excellent device characteristics more than about twice as much as the elements using Bi ₂ Te ₃ which are currently in practical use. I understood. In particular, when silver or copper was used as the metal material, it was confirmed that the performance was higher than that of other metals.

(Example 2)
In the same manner as in Example 1, laminated devices having different metal thicknesses were configured using silver and copper metal materials. The inclination angle was fixed at 20 °, and the thickness of the metal foil was changed to 70 μm, 80 μm, 85 μm, 90 μm, 95 μm, 98 μm, and 99 μm to produce a laminated structure with SrTiO ₃ with a total lamination period of 100 μm.

In this case, the ratios of SrTiO ₃ are 30%, 20%, 15%, 10%, 5%, 2%, and 1%, respectively. Table 2 shows the measurement results of the power factor of a thermoelectric device element having a thickness of 1 mm, a width of 3 mm, and a length of 20 mm produced by cutting into a 20 ° flat plate. The performance was influenced by the ratio of the thickness of SrTiO ₃ , and it was confirmed that the performance was the best around 5%. This tendency was the same for silver and copper.

Example 3
A laminated device was constructed in the same manner as in Example 1 using a 20 μm copper foil as the metal foil. A SrTiO ₃ thin film was formed on both sides of a 20 μm Cu foil while changing the film thickness from 0.125 μm to 4 μm, and thermocompression bonded. As a result, the SrTiO ₃ layer thickness was 0.25 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, An 8 μm Cu / SrTiO ₃ laminated structure was produced. When the device was fabricated with the cut-out angle set from 5 ° to 50 ° and the power factor was measured, the results shown in Table 3 were obtained.

As a result, it was confirmed that excellent device performance was obtained in the range of 0.25 μm to 8 μm with respect to the SrTiO ₃ layer thickness. This shows that favorable results are obtained when the ratio of Cu: SrTiO ₃ in the entire stacking cycle is in the range of 99: 1 to 70:30, especially 20: 1 (the ratio of SrTiO ₃ layer is about 5%), the best performance is obtained.

Taken together with this result with the results of Example 2, the performance of the laminated device rather than depend on the absolute value of the thickness and SrTiO3 layer thickness of the metal layer, the ratio of the thickness of the SrTiO ₃ layer in the overall lamination period It turns out that it depends. Further, regarding the inclination angle, it was confirmed that it exceeded 150 μW / cmK ² particularly in the range of 10 ° to 40 ° in the range of 5 ° to 50 °, and _{3 of} the elements using Bi ₂ Te ₃ which are currently in practical use. High-performance thermoelectric device elements more than doubled have been realized.

Example 4
In order to increase the mounting area and obtain a larger amount of power generation, a thermoelectric power generation device as shown in FIG. 4 using Cu as the metal 42, the connection electrode 43, and the extraction electrode 44 was produced.

A laminate made of Cu and SrTiO ₃ was produced in the same procedure as in Example 1. The laminate was configured so that Cu was 20 μm thick and SrTiO ₃ was 1 μm thick, that is, the thickness ratio of Cu and SrTiO _{3 in} the stacking direction was 100: 5, and the tilt angle was 20 °. A total of 15 laminates with a length of 50 mm, a width of 3 mm, and a thickness of 0.5 mm were produced. In addition, a plate having a thickness of 0.5 mm was used as Cu for the connection electrode 43 and the extraction electrode 44.

  Fifteen produced laminates were arranged on a support 46 made of alumina at intervals of 1 mm, and the connection electrode 43 and the extraction electrode 44 were electrically connected in series using a silver paste. At this time, in order not to cancel the electromotive force due to the heat flow, the inclined structures of the adjacent laminated bodies were arranged so as to be opposite to each other as shown in FIG. 4, and a thermoelectric power generation device of about 60 mm × 60 mm was manufactured. When the resistance value between the extraction electrodes 44 was measured, it was 0.06Ω.

The power generation characteristics of the thermoelectric power generation device of this example produced by the above procedure were evaluated. The support 46 was cooled with water from the back surface to form a low temperature part. A ceramic heater serving as a high temperature part was adhered to the other surface of the device. When the low temperature part was kept at 25 ° C. and the high temperature part was kept at 40 ° C. in such a configuration, the open end electromotive force was 1.2 V, and a high value of 239 μW / cm K ² was obtained when the power factor was estimated. As a result, a maximum of 6 W of power could be extracted from this device.

  The thermoelectric power generation device element according to the present invention has excellent power generation characteristics and can be used as a power generator using heat such as exhaust gas discharged from an automobile or a factory. It can also be applied to small portable generators.

The figure which showed the structure of the thermoelectric-power generation device element in Embodiment 1 of this invention The figure which showed the structure at the time of driving the thermoelectric generation device element in Embodiment 1 of this invention The figure which showed the example of the cut-out range at the time of cutting to the laminated structure in Embodiment 1 of this invention The figure which showed the structure of the thermoelectric power generation device in Embodiment 2 of this invention The figure which showed the structure of the thermoelectric power generation device in Embodiment 2 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st electrode 12 2nd electrode 13 Laminated body 14 SrTiO ₃ layer 15 Metal layer 16 Direction parallel to the layer 17 Opposite direction of electrode 18 Direction in which temperature gradient is generated 21 Thermoelectric device element 22 High temperature portion 23 Low temperature portion 24 Temperature gradient is Direction of occurrence 31 SrTiO ₃
32 Metal 33 Cutting range 41 SrTiO ₃
42 Metal 43 Connection electrode 44 Extraction electrode 45 Support

Claims (9)

A first electrode;
A second electrode facing the first electrode;
A laminated body sandwiched between the first electrode and the second electrode and electrically connected to both the first electrode and the second electrode;
The laminate is formed by alternately laminating SrTiO ₃ layers and metal layers,
The SrTiO ₃ layer and the metal layer are inclined at an angle θ with respect to a direction in which the first electrode and the second electrode face each other;
The angle θ is 10 ° or more and 40 ° or less,
The metal layer is made of Al, Cu, Ag, or Au;
The ratio of the thickness of the metal layer to the thickness of the SrTiO ₃ layer is in the range of 98: 2 to 90:10;
Wherein by applying a temperature difference in a direction perpendicular to the opposing direction, draws power through the first electrode and the second electrode, the heat generating device element.   The thermoelectric device element according to claim 1, wherein the metal layer is made of Cu, Ag, or Au.   The thermoelectric device element according to claim 2, wherein the metal layer is made of Cu or Ag. A first electrode;
A second electrode facing the first electrode;
A laminated body sandwiched between the first electrode and the second electrode and electrically connected to both the first electrode and the second electrode;
The laminate is formed by alternately laminating SrTiO ₃ layers and metal layers,
The SrTiO ₃ layer and the metal layer are inclined at an angle θ with respect to a direction in which the first electrode and the second electrode face each other;
The angle θ is 10 ° or more and 40 ° or less,
The metal layer is made of Al, Cu, Ag, or Au;
The ratio of the thickness of the metal layer to the thickness of the SrTiO ₃ layer is in the range of 98: 2 to 90:10;
By applying a temperature difference in a direction perpendicular to the direction of the opposite, it draws power through the first electrode and the second electrode, a manufacturing method of the thermoelectric device element, the manufacturing method below These steps include:
A laminated structure forming step of obtaining a laminated structure in which SrTiO ₃ layers and metal layers are alternately laminated;
A laminate cutout step of obtaining the laminate by cutting out the laminate structure on a surface inclined with respect to the lamination direction of the laminate structure;
An electrode forming step of forming the first electrode and the second electrode on the laminate; A first electrode;
A second electrode facing the first electrode;
A laminated body sandwiched between the first electrode and the second electrode and electrically connected to both the first electrode and the second electrode;
The laminate is formed by alternately laminating SrTiO ₃ layers and metal layers,
The SrTiO ₃ layer and the metal layer are inclined at an angle θ with respect to a direction in which the first electrode and the second electrode face each other;
The angle θ is 10 ° or more and 40 ° or less,
The metal layer is made of Al, Cu, Ag, or Au;
The thickness of the metal layer: the SrTiO ₃ layer thickness ratio of 98: a heat generating device element in the range from 2 to 90:10, power draw power through the first electrode and the second electrode A power generation method comprising the following steps:
Applying a temperature difference in a direction perpendicular to the opposing direction;   The power generation method according to claim 5, wherein the metal layer is made of Cu, Ag, or Au.   The power generation method according to claim 6, wherein the metal layer is made of Cu or Ag. A support plate, and a plurality of thermoelectric device elements provided on the support plate,
Here, each of the thermoelectric generation device elements is a thermoelectric generation device element according to claim 1,
The plurality of thermoelectric generation device elements are electrically connected in series by each connection electrode that electrically connects one end of two adjacent thermoelectric generation device elements,
An extraction electrode is connected to each of the two ends of the plurality of thermoelectric device elements that are electrically connected in series, and a temperature difference is applied along the normal direction of the support plate. A thermoelectric power generation device in which electric power is extracted via the extraction electrode. A support plate, and a plurality of thermoelectric device elements provided on the support plate,
Here, each of the thermoelectric generation device elements is a thermoelectric generation device element according to claim 1,
The plurality of thermoelectric device elements are electrically connected in parallel by two extraction electrodes that electrically connect both ends of each thermoelectric device element, and a temperature difference occurs along the normal direction of the support plate. A thermoelectric power generation device in which electric power is taken out through the take-out electrode by being applied.

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