KR102459953B1 - Thermo electric leg and thermo electric element comprising the same - Google Patents

Abstract

A thermoelectric element according to an embodiment of the present invention includes a first substrate, a plurality of first electrodes disposed on the first substrate, a plurality of first solder layers disposed on the plurality of first electrodes, and the plurality of first electrodes. a plurality of first buffer layers disposed on one solder layer, a plurality of thermoelectric legs disposed on the plurality of first buffer layers, a plurality of second buffer layers disposed on the plurality of thermoelectric legs, a plurality of second buffer layers on the plurality of second buffer layers A plurality of second solder layers disposed on the plurality of second solder layers, a plurality of second electrodes disposed on the plurality of second solder layers, and a second substrate disposed on the plurality of second electrodes, wherein the plurality of thermoelectric legs A height ratio of the plurality of first buffer layers to a height ratio of the plurality of first buffer layers, and a height ratio of the plurality of thermoelectric legs to the heights of the plurality of second buffer layers are 1 to 0.125 to 0.85, respectively.

Description

Thermoelectric leg and thermoelectric element including same

The present invention relates to a thermoelectric element, and more particularly, to a thermoelectric leg included in the thermoelectric element.

The thermoelectric phenomenon is a phenomenon that occurs by the movement of electrons and holes inside a material, and refers to direct energy conversion between heat and electricity.

A thermoelectric element is a generic term for a device using a thermoelectric phenomenon, and has a structure in which a P-type thermoelectric leg and an N-type thermoelectric leg are bonded between metal electrodes to form a PN junction pair.

Thermoelectric devices can be divided into devices using a temperature change in electrical resistance, devices using the Seebeck effect, a phenomenon in which electromotive force is generated by a temperature difference, and devices using the Peltier effect, which is a phenomenon in which heat absorption or heat is generated by current. .

Thermoelectric devices are widely applied to home appliances, electronic parts, and communication parts. For example, the thermoelectric element may be applied to an apparatus for cooling, an apparatus for heating, an apparatus for power generation, and the like. Accordingly, the demand for the thermoelectric performance of the thermoelectric element is increasing.

In general, a thermoelectric element includes a substrate, an electrode, and a thermoelectric leg, a plurality of thermoelectric legs are disposed between an upper substrate and a lower substrate in an array form, and a plurality of upper electrodes are disposed between the plurality of thermoelectric legs and the upper substrate, , a plurality of lower electrodes are disposed between the plurality of thermoelectric legs and the lower substrate.

1 shows a correlation between a height of a thermoelectric leg and an output power (out power). This simulates the output power according to the height of the thermoelectric leg under the conditions of a high temperature part temperature of 473K, a low temperature part temperature of 308K, and dT 165K for a 40mm*40mm thermoelectric element including 127 pairs of thermoelectric legs each having a size of 1.7mm*1.7mm. is a result 2 shows the correlation between the height of the thermoelectric leg and the maximum stress. This is the maximum stress according to the height of the thermoelectric leg under the conditions of a high temperature part temperature of 500K, a low temperature part temperature of 300K, and dT (200K) for a 40mm*40mm thermoelectric element including 127 pairs of thermoelectric legs each having a size of 1.7mm*1.7mm. is the simulation result. Here, the maximum stress may mean a maximum internal stress in the bonding material.

Referring to FIG. 1 , the lower the height of the thermoelectric leg, the higher the output power. Accordingly, it can be seen that the amount of power generation increases as the height of the thermoelectric leg decreases. When the thermoelectric element is a Peltier element, it can be seen that the maximum heat absorption increases as the height of the thermoelectric leg decreases.

However, referring to FIG. 2 , as the height of the thermoelectric leg decreases, the stress applied to the junction between the thermoelectric leg and the electrode increases. That is, when the thermoelectric element is driven, the temperature of the high temperature part increases, and accordingly, the substrate and the electrode on the high temperature part thermally expand. Since the coefficient of thermal expansion of the electrode on the high temperature side is different from the coefficient of thermal expansion of the thermoelectric leg in contact with the electrode on the side of the high temperature side, stress is generated in the contact surface between the electrode on the high temperature side and the thermoelectric leg. As the height of the thermoelectric leg is lowered, that is, as the stress is increased, the angle at which the thermoelectric leg is tilted is increased, thereby reducing the reliability of the thermoelectric element.

An object of the present invention is to provide a thermoelectric device having excellent thermoelectric performance and a thermoelectric leg included therein.

A thermoelectric element according to an embodiment of the present invention includes a first substrate, a plurality of first electrodes disposed on the first substrate, a plurality of first solder layers disposed on the plurality of first electrodes, and the plurality of first electrodes. a plurality of first buffer layers disposed on one solder layer, a plurality of thermoelectric legs disposed on the plurality of first buffer layers, a plurality of second buffer layers disposed on the plurality of thermoelectric legs, a plurality of second buffer layers on the plurality of second buffer layers A plurality of second solder layers disposed on the plurality of second solder layers, a plurality of second electrodes disposed on the plurality of second solder layers, and a second substrate disposed on the plurality of second electrodes, wherein the plurality of thermoelectric legs A height ratio of the plurality of first buffer layers to a height ratio of the plurality of first buffer layers, and a height ratio of the plurality of thermoelectric legs to the heights of the plurality of second buffer layers are 1 to 0.125 to 0.85, respectively.

The linear expansion coefficients of the plurality of first buffer layers and the linear expansion coefficients of the plurality of second buffer layers may be greater than the linear expansion coefficients of the plurality of thermoelectric legs.

The linear expansion coefficients of the plurality of first buffer layers and the linear expansion coefficients of the plurality of second buffer layers may be smaller than the linear expansion coefficients of the plurality of first solder layers and the linear expansion coefficients of the plurality of second solder layers.

A ratio of heights of the plurality of thermoelectric legs to heights of the plurality of first buffer layers and a ratio of heights of the plurality of thermoelectric legs to heights of the plurality of second buffer layers may be 1:1 to 0.375 to 0.625, respectively.

The plurality of first buffer layers and the plurality of second buffer layers may include aluminum.

Each of the plurality of first buffer layers and the plurality of second buffer layers may include an aluminum layer and a nickel plating layer disposed on the aluminum layer, and the nickel plating layer may be disposed to face the plurality of thermoelectric legs.

Widths of the plurality of first buffer layers and widths of the plurality of second buffer layers may be smaller than widths of the plurality of thermoelectric legs.

Each of the plurality of first buffer layers and the plurality of second buffer layers may be disposed in an area spaced apart from an edge of each of the plurality of thermoelectric legs by a predetermined distance.

Each of the plurality of first buffer layers and the plurality of second buffer layers is disposed in an area spaced apart from one side of each of the plurality of thermoelectric legs by a first distance and spaced apart by a second distance from the other side opposite to the one side. and the first distance and the second distance may be different from each other.

Each of the plurality of first buffer layers and the plurality of second buffer layers may have a height of 0.2 to 1 mm.

The plurality of thermoelectric legs may include a P-type thermoelectric leg and an N-type thermoelectric leg.

According to an embodiment of the present invention, it is possible to obtain a thermoelectric device having excellent thermoelectric performance and maintaining high reliability and durability even in frequent temperature changes. In particular, it is possible to obtain a thermoelectric leg stably coupled to the electrode and providing excellent thermoelectric performance.

1 shows a correlation between a height of a thermoelectric leg and an output power (out power).
2 shows the correlation between the height of the thermoelectric leg and the maximum stress.
3 is a cross-sectional view of the thermoelectric element, and FIG. 4 is a perspective view of the thermoelectric element.
5 is a cross-sectional view of a thermoelectric leg and an electrode according to an embodiment of the present invention.
6 to 7 show a method of manufacturing a thermoelectric leg having a stacked structure.
8 illustrates a conductive layer formed between unit members in the laminate structure of FIGS. 6 to 7 .
9(a) is a cross-sectional view of a thermoelectric element according to an embodiment of the present invention, and FIG. 9(b) is a cross-sectional view of a thermoelectric leg according to an embodiment of the present invention.
10 is a view for explaining a tilting angle of a thermoelectric element according to an embodiment of the present invention and a thermoelectric element according to a comparative example.
11 is a cross-sectional view of a thermoelectric leg according to another embodiment of the present invention.
12 is a cross-sectional view of a thermoelectric leg according to another embodiment of the present invention.
13 to 14 are cross-sectional views of a thermoelectric element according to still another embodiment of the present invention.
15 is a simulation result of maximum stress according to a height of a thermoelectric leg and a height of a buffer layer of a thermoelectric element according to an embodiment of the present invention.
16 is a simulation result of maximum stress according to a width of a thermoelectric leg and a height of a buffer layer of a thermoelectric device according to an embodiment of the present invention.
17 is a block diagram of a water purifier to which a thermoelectric element is applied according to an embodiment of the present invention.
18 is a block diagram of a refrigerator to which a thermoelectric element is applied according to an embodiment of the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated and described in the drawings. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Terms including an ordinal number such as second, first, etc. may be used to describe various elements, but the elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as the first component, and similarly, the first component may also be referred to as the second component. and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It is to be understood that this does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Hereinafter, the embodiment will be described in detail with reference to the accompanying drawings, but the same or corresponding components are given the same reference numerals regardless of the reference numerals, and the overlapping description thereof will be omitted.

3 is a cross-sectional view of the thermoelectric element, and FIG. 4 is a perspective view of the thermoelectric element.

3 to 4 , the thermoelectric element 100 includes a lower substrate 110 , a lower electrode 120 , a P-type thermoelectric leg 130 , an N-type thermoelectric leg 140 , an upper electrode 150 , and an upper substrate. (160).

The lower electrode 120 is disposed between the lower substrate 110 and the lower bottom surfaces of the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 , and the upper electrode 150 is formed between the upper substrate 160 and the P-type thermoelectric leg 140 . It is disposed between the thermoelectric leg 130 and the upper bottom surface of the N-type thermoelectric leg 140 . Accordingly, the plurality of P-type thermoelectric legs 130 and the plurality of N-type thermoelectric legs 140 are electrically connected by the lower electrode 120 and the upper electrode 150 . A pair of P-type thermoelectric legs 130 and N-type thermoelectric legs 140 disposed between the lower electrode 120 and the upper electrode 150 and electrically connected may form a unit cell.

For example, when a voltage is applied to the lower electrode 120 and the upper electrode 150 through the lead wires 181 and 182 , a current flows from the P-type thermoelectric leg 130 to the N-type thermoelectric leg 140 due to the Peltier effect. The substrate through which flows absorbs heat to act as a cooling unit, and the substrate through which current flows from the N-type thermoelectric leg 140 to the P-type thermoelectric leg 130 may be heated and act as a heating unit.

Here, the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 may be bismuth telluride (Bi-Te)-based thermoelectric legs including bismuth (Bi) and tellurium (Te) as main raw materials. P-type thermoelectric leg 130 is antimony (Sb), nickel (Ni), aluminum (Al), copper (Cu), silver (Ag), lead (Pb), boron (B), gallium with respect to 100wt% of the total weight A mixture containing 99 to 99.999 wt% of a bismuth telluride (Bi-Te)-based main raw material containing at least one of (Ga), tellurium (Te), bismuth (Bi) and indium (In) and Bi or Te 0.001 It may be a thermoelectric leg comprising 1 wt % to 1 wt %. For example, the main raw material is Bi-Se-Te, and Bi or Te may be further included in an amount of 0.001 to 1 wt% of the total weight. N-type thermoelectric leg 140 is selenium (Se), nickel (Ni), aluminum (Al), copper (Cu), silver (Ag), lead (Pb), boron (B), gallium with respect to 100wt% of the total weight A mixture containing 99 to 99.999 wt% of a bismuth telluride (Bi-Te)-based main raw material containing at least one of (Ga), tellurium (Te), bismuth (Bi) and indium (In) and Bi or Te 0.001 It may be a thermoelectric leg comprising 1 wt % to 1 wt %. For example, the main raw material is Bi-Sb-Te, and may further include Bi or Te in an amount of 0.001 to 1 wt% of the total weight.

The P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 may be formed in a bulk type or a stack type. In general, the bulk-type P-type thermoelectric leg 130 or the bulk-type N-type thermoelectric leg 140 heat-treats a thermoelectric material to manufacture an ingot, grinds the ingot and sieves to obtain powder for the thermoelectric leg, and then It can be obtained through the process of sintering and cutting the sintered body. The laminated P-type thermoelectric leg 130 or the laminated N-type thermoelectric leg 140 is formed by applying a paste containing a thermoelectric material on a sheet-shaped substrate to form a unit member, and then stacking and cutting the unit member. can be obtained

In this case, the pair of P-type thermoelectric legs 130 and N-type thermoelectric legs 140 may have the same shape and volume, or may have different shapes and volumes. For example, since the electrical conductivity properties of the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 are different, the height or cross-sectional area of the N-type thermoelectric leg 140 is calculated as the height or cross-sectional area of the P-type thermoelectric leg 130 . may be formed differently.

The performance of the thermoelectric element according to an embodiment of the present invention may be expressed as a Seebeck index. The Seebeck index (ZT) may be expressed as in Equation (1).

Here, α is the Seebeck coefficient [V/K], σ is the electrical conductivity [S/m], and α ² σ is the power factor (Power Factor, [W/mK ² ]). And, T is the temperature, k is the thermal conductivity [W/mK]. k can be expressed as a·c _p ·ρ, a is the thermal diffusivity [cm ² /S], c _p is the specific heat [J/gK], ρ is the density [g/cm ³ ].

In order to obtain the Seebeck index of the thermoelectric element, a Z value (V/K) is measured using a Z meter, and the Seebeck index (ZT) can be calculated using the measured Z value.

Here, the lower electrode 120 is disposed between the lower substrate 110 and the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 , and the upper substrate 160 and the P-type thermoelectric leg 130 and the N-type thermoelectric leg 130 . The upper electrode 150 disposed between the thermoelectric legs 140 includes at least one of copper (Cu), silver (Ag), aluminum (Al), and nickel (Ni), and has a thickness of 0.01 mm to 0.3 mm. can When the thickness of the lower electrode 120 or the upper electrode 150 is less than 0.01 mm, the function as an electrode may deteriorate and the electrical conduction performance may be lowered. If it exceeds 0.3 mm, the conduction efficiency may be lowered due to an increase in resistance. .

In addition, the lower substrate 110 and the upper substrate 160 facing each other may be an insulating substrate or a metal substrate. The insulating substrate may be an alumina substrate or a flexible polymer resin substrate. The flexible polymer resin substrate has high permeability such as polyimide (PI), polystyrene (PS), polymethyl methacrylate (PMMA), cyclic olefin copoly (COC), polyethylene terephthalate (PET), and resin. Various insulating resin materials such as plastic may be included. For example, the lower substrate 110 and the upper substrate 160 may be formed of an epoxy resin composition including an epoxy resin and an inorganic filler. In this case, the thickness of the lower substrate 110 and the upper substrate 160 may be 0.02 to 0.6 mm, preferably 0.1 to 0.6 mm, more preferably 0.2 to 0.6 mm, and the thermal conductivity is 1 W/mK or more, preferably Preferably it may be 10W/mK or more, more preferably 20W/mK or more. When the thicknesses of the lower substrate 110 and the upper substrate 160 satisfy these numerical ranges, the lower substrate 110 even if the thicknesses of the lower substrate 110 and the upper substrate 160 repeatedly contract and expand according to the temperature change. ) and the support (not shown) or heat sink (not shown) on which the upper substrate 160 is mounted may not be affected.

To this end, the epoxy resin may include an epoxy compound and a curing agent. In this case, the curing agent may be included in a volume ratio of 1 to 10 with respect to 10 volume ratio of the epoxy compound. Here, the epoxy compound may include at least one of a crystalline epoxy compound, an amorphous epoxy compound, and a silicone epoxy compound. The crystalline epoxy compound may include a mesogen structure. A mesogen is a basic unit of a liquid crystal and includes a rigid structure. And, the amorphous epoxy compound may be a conventional amorphous epoxy compound having two or more epoxy groups in the molecule, for example, may be a glycidyl ether product derived from bisphenol A or bisphenol F. Here, the curing agent may include at least one of an amine-based curing agent, a phenol-based curing agent, an acid anhydride-based curing agent, a polymercaptan-based curing agent, a polyaminoamide-based curing agent, an isocyanate-based curing agent, and a block isocyanate-based curing agent, and two or more curing agents may be used in combination.

The inorganic filler may include aluminum oxide and nitride, and the nitride may include at least one of boron nitride and aluminum nitride. Here, the boron nitride may be a boron nitride aggregate in which plate-shaped boron nitride is aggregated, and the surface of the boron nitride aggregate is coated with a polymer having the following unit 1, or at least a portion of the pores in the boron nitride aggregate is in the polymer having the following unit 1 can be charged by

Unit 1 is as follows.

[Unit 1]

wherein one of R ¹ , R ² , R ³ and R ⁴ is H, and the other is selected from the group consisting of C ₁ -C ₃ alkyl, C ₂ -C ₃ alkene and C ₂ -C ₃ alkyne, and R ⁵ may be a linear, branched or cyclic divalent organic linker having 1 to 12 carbon atoms.

In one embodiment, one of R ¹ , R ² , R ³ , and R ⁴ other than H is selected from C ₂ -C ₃ alkene, and the other and the other one of the other is selected from C ₁ -C ₃ alkyl. can be selected. For example, the polymer according to an embodiment of the present invention may include the following unit 2.

[Unit 2]

Alternatively, the remainder of R ¹ , R ² , R ³ and R ⁴ except for H may be selected to be different from each other from the group consisting of C ₁ -C ₃ alkyl, C ₂ -C ₃ alkene, and C ₂ -C ₃ alkyne. have.

In this way, when the polymer according to Unit 1 or Unit 2 is coated on the boron nitride agglomerate in which plate-shaped boron nitride is aggregated, and at least a portion of the voids in the boron nitride agglomerate is filled, the air layer in the boron nitride agglomerate is minimized to minimize the amount of the boron nitride agglomerate. It is possible to increase the thermal conduction performance and to prevent the cracking of the boron nitride agglomerates by increasing the bonding force between the plate-shaped boron nitrides. And, when the coating layer is formed on the boron nitride agglomerate in which the plate-shaped boron nitride is agglomerated, it is easy to form a functional group, and when the functional group is formed on the coating layer of the boron nitride agglomerate, affinity with the resin can be increased.

As such, when the lower substrate 110 and the upper substrate 160 are made of an epoxy resin composition, a separate adhesive or physical fastening means is required when bonding to a heat sink or a metal support due to the adhesive performance of the epoxy resin composition itself. don't Accordingly, the overall size of the thermoelectric element can be reduced.

Alternatively, the insulating substrate may be a fabric. The metal substrate may include Al, Al alloy, Cu, Cu alloy or Cu-Al alloy. In addition, when the lower substrate 110 and the upper substrate 160 are metal substrates, a dielectric layer 170 is disposed between the lower substrate 110 and the lower electrode 120 and between the upper substrate 160 and the upper electrode 150 , respectively. This can be further formed. The dielectric layer 170 may include a material having a thermal conductivity of 5 to 50 W/K.

In this case, the sizes of the lower substrate 110 and the upper substrate 160 may be different. For example, the volume, thickness, or area of one of the lower substrate 110 and the upper substrate 160 may be larger than the volume, thickness, or area of the other. Accordingly, heat absorbing performance or heat dissipation performance of the thermoelectric element may be improved.

In addition, a heat dissipation pattern, for example, a concave-convex pattern, may be formed on the surface of at least one of the lower substrate 110 and the upper substrate 160 . Accordingly, the heat dissipation performance of the thermoelectric element may be improved. When the concave-convex pattern is formed on a surface in contact with the P-type thermoelectric leg 130 or the N-type thermoelectric leg 140 , bonding characteristics between the thermoelectric leg and the substrate may also be improved.

Meanwhile, the P-type thermoelectric leg 130 or the N-type thermoelectric leg 140 may have a cylindrical shape, a polygonal column shape, an elliptical column shape, or the like.

According to an embodiment of the present invention, the P-type thermoelectric leg 130 or the N-type thermoelectric leg 140 may be formed to have a wide width at a portion bonding to the electrode.

5 is a cross-sectional view of a thermoelectric leg and an electrode according to an embodiment of the present invention.

Referring to FIG. 5 , the thermoelectric leg 130 is disposed at a position opposite to the first element part 132 and the first element part 132 having a first cross-sectional area, and the second element part 136 has a second cross-sectional area. ), and a connection part 134 connecting the first element part 132 and the second element part 136 and having a third cross-sectional area. In this case, the cross-sectional area of the connection part 134 in an arbitrary area in the horizontal direction may be smaller than the first cross-sectional area or the second cross-sectional area.

In this way, when the cross-sectional areas of the first element part 132 and the second element part 136 are formed to be larger than the cross-sectional areas of the connection part 134 , the first element part 132 and the second element part 132 and the second element part 136 are made of the same amount of material. The temperature difference T between the parts 136 may be large. Accordingly, since the amount of free electrons moving between the hot side and the cold side increases, the amount of power generation increases, and the heating efficiency or cooling efficiency increases.

At this time, the width (B) of the cross-section having the longest width among the horizontal cross-sections of the connection part 134 and the width (A or The ratio between C) may be 1:(1.5-4). Accordingly, power generation efficiency, heat generation efficiency, or cooling efficiency can be increased.

Here, the first element part 132 , the second element part 136 , and the connection part 134 may be integrally formed using the same material.

The thermoelectric leg according to an embodiment of the present invention may have a stacked structure. For example, the P-type thermoelectric leg or the N-type thermoelectric leg may be formed by stacking a plurality of structures coated with a semiconductor material on a sheet-shaped substrate and then cutting them. Accordingly, it is possible to prevent material loss and improve electrical conductivity properties.

6 shows a method of manufacturing a thermoelectric leg having a stacked structure.

Referring to FIG. 6 , a semiconductor layer 1120 is formed by manufacturing a material including a semiconductor material in the form of a paste and then applying it on a substrate 1110 such as a sheet or a film. Accordingly, one unit member 1100 may be formed.

A multilayer structure 1200 is formed by stacking a plurality of unit members 1100a, 1100b, 1100c, and 1100d, and then the unit thermoelectric leg 1300 can be obtained by cutting it.

As described above, the unit thermoelectric leg 1300 may be formed by a structure in which a plurality of unit members 1100 having a semiconductor layer 1120 formed on a substrate 1110 are stacked.

Here, the process of applying the paste on the substrate 1110 may be performed in various ways. For example, it may be performed by a tape casting method. In the tape casting method, a powder of a fine semiconductor material is mixed with at least one selected from an aqueous or non-aqueous solvent, a binder, a plasticizer, a dispersant, a defoamer, and a surfactant to form a slurry It is a method of molding on a moving blade or a moving substrate after manufacturing in a (slurry) form. In this case, the substrate 1110 may be a film or sheet having a thickness of 10 μm to 100 μm, and as the applied semiconductor material, the P-type thermoelectric material or the N-type thermoelectric material for manufacturing the bulk-type device described above may be applied as it is.

The process of arranging and stacking the unit members 1100 in a plurality of layers may be performed by pressing at a temperature of 50 to 250° C., and the number of the unit members 1100 to be stacked is, for example, 2 to 50 days. can Thereafter, it may be cut to a desired shape and size, and a sintering process may be added.

The unit thermoelectric leg 1300 manufactured in this way can ensure uniformity of thickness, shape, and size, advantageously reduce the thickness, and reduce material loss.

The unit thermoelectric leg 1300 may have a cylindrical shape, a polygonal column shape, an elliptical column shape, or the like, and may be cut into a shape as illustrated in FIG. 6( d ).

Meanwhile, the unit thermoelectric leg 1300 may be cut in the direction shown in FIG. 7 . According to this structure, it is possible to lower the heat conduction efficiency in the vertical direction and at the same time improve the electric conduction characteristics, thereby increasing the cooling efficiency.

Meanwhile, in order to manufacture a thermoelectric leg having a stacked structure, a conductive layer may be further formed on one surface of the unit member 1100 .

8 illustrates a conductive layer formed between unit members in the laminate structure of FIGS. 6 to 7 . The conductive layer (C) may be formed on the opposite surface of the substrate 1110 on which the semiconductor layer 1120 is formed, and may be patterned such that a portion of the surface of the substrate 1110 is exposed.

As shown in FIGS. 8(a) and 8(b), a mesh-type structure including closed opening patterns c1 and c2, or as shown in FIGS. 8(c) and 8(d), It may be variously modified into a line-type structure including the open opening patterns c3 and c4.

Such a conductive layer (C) can increase the adhesion between the unit members in the unit thermoelectric leg formed in a laminated structure of the unit members, lower the thermal conductivity between the unit members, and can improve the electrical conductivity. The conductive layer (C) may be a metal material, for example, Cu, Ag, Ni, etc. may be applied.

According to an embodiment of the present invention, for stable coupling between the thermoelectric leg and the electrode, a buffer layer is formed on both surfaces of the thermoelectric leg.

9(a) is a cross-sectional view of a thermoelectric element according to an embodiment of the present invention, and FIG. 9(b) is a cross-sectional view of a thermoelectric leg according to an embodiment of the present invention. 10 is a view for explaining a tilting angle of a thermoelectric element according to an embodiment of the present invention and a thermoelectric element according to a comparative example. 11 is a cross-sectional view of a thermoelectric leg according to another embodiment of the present invention, and FIG. 12 is a cross-sectional view of a thermoelectric leg according to another embodiment of the present invention.

Referring to FIGS. 9A and 9B , the thermoelectric element 900 according to an embodiment of the present invention includes a first substrate 910 and a first electrode 920 disposed on the first substrate 910 . ), the first solder layer 930 disposed on the first electrode 920 , the first buffer layer 940 disposed on the first solder layer 930 , and the P-type disposed on the first buffer layer 940 . A second buffer layer 960 disposed on the thermoelectric leg 950 and the N-type thermoelectric leg 952 , the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 , the second buffer layer 960 disposed on the second buffer layer 960 . A second solder layer 970 , a second electrode 980 disposed on the second solder layer 970 , and a second substrate 990 disposed on the second electrode 980 .

The first substrate 910 , the first electrode 920 , the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 , the second electrode 980 , and the second substrate 990 are shown in FIGS. 3 to 4 , respectively. It may correspond to the lower substrate 110 , the lower electrode 120 , the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 , the upper electrode 150 and the upper substrate 160 , and the same content in this regard A duplicate description will be omitted.

In FIG. 9B , only the P-type thermoelectric leg 950 is exemplified for convenience of description, but the present invention is not limited thereto, and the same structure may be applied to the N-type thermoelectric leg 952 .

According to an embodiment of the present invention, buffer layers 940 and 960 may be disposed at both ends of the P-type thermoelectric leg 950 . That is, a first buffer layer 940 is disposed between the first solder layer 930 and the P-type thermoelectric leg 950 , and a second buffer layer ( ) is disposed between the P-type thermoelectric leg 950 and the second solder layer 970 . 960) may be disposed. Here, each of the height h1 of the first buffer layer 940 and the height h2 of the second buffer layer 960 may be 0.2 to 1 mm. If the height h1 of the first buffer layer 940 and the height h2 of the second buffer layer 960 are less than 0.2 mm, it is difficult to function as a buffer layer, and the height h1 of the first buffer layer 940 and the height h2 of the first buffer layer 940 are less than 0.2 mm. When the height h2 of each of the two buffer layers 960 exceeds 1 mm, the buffer layer is easily peeled off.

The linear expansion coefficient of the first buffer layer 940 and the linear expansion coefficient of the second buffer layer 960 are greater than the linear expansion coefficient of the P-type thermoelectric leg 950 , and the linear expansion coefficient of the first solder layer 930 and the second solder layer 970 . ) is smaller than the coefficient of linear expansion. Here, the coefficient of linear expansion means a value obtained by dividing a length increase rate due to thermal expansion by a temperature difference. For example, the coefficient of linear expansion of the metal may mean a rate at which the length of the metal increases with respect to an increase in the temperature of the metal by 1°C. In general, the linear expansion coefficient of lead is 29*10 ^-6 /°C, and the first solder layer 930 and the second solder layer 970 may be made of lead. And, the coefficient of linear expansion of the thermoelectric leg is about 10 to 15 * 10 ^-6 /℃. Accordingly, the coefficients of linear expansion of the first buffer layer 940 and the second buffer layer 960 may be 18 to 26*10 ^-6 /°C, preferably 20 to 25*10 ^-6 /°C. When the linear expansion coefficient of the first buffer layer 940 and the linear expansion coefficient of the second buffer layer 960 are out of these numerical ranges, the linear expansion coefficient of the P-type thermoelectric leg 950 and the first buffer layer 940 and the second buffer layer 960 are ) increases, or the difference between the coefficients of linear expansion of the first buffer layer 940 and the second buffer layer 960 and the coefficients of linear expansion of the first solder layer 930 and the second solder layer 970 is large. As a result, the P-type thermoelectric leg 950 may be excessively tilted or peeled off.

Accordingly, the first buffer layer 940 and the second buffer layer 960 may include aluminum (Al) or silver (Ag).

In this case, the ratio of the height H of the P-type thermoelectric leg 950 to the height h1 of the first buffer layer 940 may be 1 to 0.125 to 0.85, preferably 1 to 0.375 to 0.625. Similarly, the ratio of the height H of the P-type thermoelectric leg 950 to the height h2 of the second buffer layer 960 may be in a range of 1 to 0.125 to 0.85, preferably 1 to 0.375 to 0.625. As described above, the first buffer layer 940 is disposed between the P-type thermoelectric leg 950 and the first solder layer 930 , and the second buffer layer is disposed between the P-type thermoelectric leg 950 and the second solder layer 970 . When 960 is disposed, the distance between the first solder layer 930 and the second solder layer 970 may be maintained larger by h1+h2 compared to the actual height H of the P-type thermoelectric leg 950 .

When the thermoelectric element is driven, the high temperature portion, for example, the second substrate 990 side may thermally expand. As shown in FIG. 10( a ), as shown in FIG. 10( b ), compared to the case where both ends of the thermoelectric element according to the comparative example, that is, the thermoelectric leg having a height of H, directly contact the solder layer, as shown in FIG. When the first buffer layer 940 and the second buffer layer 960 having heights h1 and h2, respectively, are further disposed at both ends of the thermoelectric element according to the embodiment, that is, a thermoelectric leg having a height of H, the tilting angle may be reduced. .

That is, according to an embodiment of the present invention, the reliability of the thermoelectric element can be improved by reducing the tilting angle of the thermoelectric leg while increasing the output power by maintaining the height of the thermoelectric leg at a low level.

At this time, when the ratio of the height H of the P-type thermoelectric leg 950 to the height h1 of the first buffer layer 940 is out of this numerical range, for example, the height h1 of the first buffer layer 940 is When the ratio of the height H of the P-type thermoelectric leg 950 to the height h1 of the first buffer layer 940 is lower than the lower limit, it may be difficult to obtain a desired level of reliability. In addition, when the height h1 of the first buffer layer 940 is higher than the upper limit of the ratio of the height H of the P-type thermoelectric leg 950 to the height h1 of the first buffer layer 940 , the first buffer layer 940 . ) is more likely to peel off.

Meanwhile, referring to FIG. 11 , each of the first buffer layer 940 and the second buffer layer 960 may further include a nickel plating layer. For example, when each of the first buffer layer 940 and the second buffer layer 960 includes aluminum layers 942 and 962 , the nickel plating layers 944 and 964 are formed on the aluminum layers 942 and 964 with the P-type thermoelectric layer. It may be disposed to face the leg 950 . In this case, the nickel plating layers 944 and 964 may be formed by etching the aluminum layers 942 and 964 . Here, the nickel plating layers 944 and 964 may have a thickness of 1 to 20 μm, preferably 1 to 10 μm. Since the nickel plating layers 944 and 964 prevent a reaction between Bi or Te, which is a semiconductor material in the P-type thermoelectric leg 950 , and the aluminum layers 942 and 962 in the first buffer layer 940 and the second buffer layer 960 , In addition to preventing degradation of the performance of the thermoelectric element, oxidation of the aluminum layers 942 and 962 in the first buffer layer 940 and the second buffer layer 960 can be prevented.

Referring to FIG. 12 , bonding layers 946 and 966 may be further disposed between the P-type thermoelectric leg 950 and the nickel plating layer 944 and between the P-type thermoelectric leg 950 and the nickel plating layer 964 . In this case, the bonding layers 946 and 966 may include Te. For example, the bonding layers 946 and 966 may include at least one of Ni-Te, Sn-Te, Ti-Te, Fe-Te, Sb-Te, Cr-Te, and Mo-Te. According to an embodiment of the present invention, each of the bonding layers 946 and 966 may have a thickness of 0.5 to 100 μm, preferably 1 to 50 μm. When the thickness of the bonding layer exceeds the upper limit of this numerical range, the resistance change rate may rapidly increase.

In general, among the semiconductor materials included in the P-type thermoelectric leg 950 , Te tends to diffuse into the nickel plating layers 944 and 964 . When Te in the P-type thermoelectric leg 950 is diffused into the nickel plating layers 944 and 964, in the vicinity of the boundary between the P-type thermoelectric leg 950 and the nickel plating layers 944 and 964, a region in which Bi is more distributed than Te ( Hereinafter, a Bi-rich region) may occur. Due to the Bi-rich region, the resistance in the P-type thermoelectric leg 950 is increased, and as a result, the performance of the thermoelectric element may be deteriorated.

However, according to the embodiment of the present invention, bonding layers 946 and 966 including Te are preliminarily disposed between the P-type thermoelectric leg 950 and the nickel plating layers 944 and 964, and the P-type thermoelectric leg 950 . It is possible to prevent the internal Te from diffusing into the nickel plating layers 944 and 964 . Accordingly, the occurrence of the Bi-rich region can be prevented.

13 to 14 are cross-sectional views of a thermoelectric element according to still another embodiment of the present invention. Here, redundant descriptions of the same contents as those of FIGS. 9 to 12 will be omitted.

13 to 14 , the width W2 of the first buffer layer 940 and the second buffer layer 960 is greater than the width W1 of the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 . can be small For example, each of the first buffer layer 940 and the second buffer layer 960 may be disposed in an area spaced apart from the edges of each of the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 by a predetermined distance. That is, each of the first buffer layer 940 and the second buffer layer 960 is spaced apart from one side of each of the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 by a first distance d1, and on one side It may be disposed in an area spaced apart by a second distance d2 from the other side facing it.

As such, when the width of the first buffer layer 940 and the width of the second buffer layer 960 are smaller than the width of the P-type thermoelectric leg 950 and the width of the N-type thermoelectric leg 952 , the thermoelectric element is driven. Even if the first buffer layer 940 or the second buffer layer 960 thermally expands due to an increase in the temperature of the high temperature portion, the tilt angle of the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 may be minimized. In particular, as shown in FIG. 14 , the first distance d1 and the second distance d2 may be different. For example, the distance between the side surfaces of the P-type thermoelectric leg 950 and the N-type thermoelectric leg 952 that is disposed toward the edge of the thermoelectric element 900 and the first buffer layer 940 and the second buffer layer 960 is The distance between the side surface of the thermoelectric element 900 toward the center and the first buffer layer 940 and the second buffer layer 960 may be greater than the distance. According to this, even if the temperature of the high temperature part is increased by the driving of the thermoelectric element, and the first buffer layer 940 or the second buffer layer 960 thermally expands toward the edge of the thermoelectric element 900, the P-type thermoelectric leg 950 and An angle at which the N-type thermoelectric leg 952 is tilted may be minimized.

15 is a simulation result of maximum stress according to a height of a thermoelectric leg and a height of a buffer layer of a thermoelectric element according to an embodiment of the present invention, and FIG. 16 is a width of a thermoelectric leg of a thermoelectric element according to an embodiment of the present invention. and a simulation result of the maximum stress according to the height of the buffer layer.

15, the height of the thermoelectric leg under the conditions of a high temperature part temperature of 500K, a low temperature part temperature of 300K and dT (200K) for a 40mm*40mm thermoelectric element including 127 pairs of thermoelectric legs each having a size of 1.7mm*1.7mm (200K) It is the result of simulating the maximum stress according to the height (h) of the buffer layer for each H).

In FIG. 16 , the width (W) of the thermoelectric leg under the conditions of a high temperature part temperature of 500K, a low temperature part temperature of 300K and dT (200K) for a 40mm*40mm thermoelectric element including 127 pairs of thermoelectric legs having a height (H) of 1.6mm (W) It is the result of simulating the maximum stress according to the height (h) of the buffer layer for each.

15, the height (H) of the thermoelectric leg is 1.6 mm and the height (h) of the buffer layer is 0.2 mm or more, the height (H) of the thermoelectric leg is 1.2 mm, and the height (h) of the buffer layer is 0.2 mm or more The condition, and the condition that the height (H) of the thermoelectric leg is 0.8 mm and the height (h) of the buffer layer is 0.3 mm, that is, the ratio between the height (H) of the thermoelectric leg and the height (h) of the buffer layer is 1:0.125 to 1.25 It can be seen that the maximum stress is obtained as 1.6*10 ⁸ Pa under

In particular, the height (H) of the thermoelectric leg is 1.6 mm and the height (h) of the buffer layer is 0.4 mm or more, the height (H) of the thermoelectric leg is 1.2 mm, and the height (h) of the buffer layer is 0.6 mm or more, that is, the thermoelectric leg It can be seen that the maximum stress is lower under the condition that the ratio between the height of the leg (H) and the height (h) of the buffer layer is 1:0.25 to 0.85.

In particular, under the condition that the height (H) of the thermoelectric leg is 1.6 mm and the height (h) of the buffer layer is 0.6 mm or more, that is, the ratio between the height (H) of the thermoelectric leg and the height (h) of the buffer layer is 1:0.375 to 0.625 It can be seen that the maximum stress is lowered to about 1.4*10 ⁸ Pa.

Referring to FIG. 16 , under the condition that the height (H) of the thermoelectric leg is 1.6 mm, when the width (W) of the thermoelectric leg is 1.7 mm and the height of the buffer layer is 0.2 mm or more, the width (W) of the thermoelectric leg is 1.4 mm and when the height of the buffer layer is about 0.25 mm or more, it can be seen that when the width (W) of the thermoelectric leg is 1 mm and the height of the buffer layer is 1 mm, the maximum stress is lowered to about 1.6*10 ⁸ Pa.

That is, it can be seen that when the height h of the thermoelectric leg is fixed, the maximum stress decreases as the width W of the thermoelectric leg increases.

Hereinafter, an example in which a thermoelectric element according to an embodiment of the present invention is applied to a water purifier will be described with reference to FIG. 17 .

17 is a block diagram of a water purifier to which a thermoelectric element is applied according to an embodiment of the present invention.

The water purifier 1 to which the thermoelectric element is applied according to an embodiment of the present invention includes a raw water supply pipe 12a, a purified water tank inlet pipe 12b, a purified water tank 12, a filter assembly 13, a cooling fan 14, and a heat storage tank ( 15), a cold water supply pipe 15a, and a thermoelectric device 1000.

The raw water supply pipe 12a is a supply pipe for introducing water to be purified from a water source into the filter assembly 13 , and the purified water tank inlet pipe 12b is an inflow for introducing water purified from the filter assembly 13 into the purified water tank 12 . The cold water supply pipe 15a is a supply pipe through which the cold water cooled to a predetermined temperature by the thermoelectric device 1000 in the purified water tank 12 is finally supplied to the user.

The purified water tank 12 temporarily receives purified water to store and supply the purified water through the filter assembly 13 and introduced through the purified water tank inlet pipe 12b to the outside.

The filter assembly 13 includes a precipitation filter 13a, a pre-carbon filter 13b, a membrane filter 13c, and a post-carbon filter 13d.

That is, water flowing into the raw water supply pipe 12a may pass through the filter assembly 13 and be purified.

The heat storage tank 15 is disposed between the purified water tank 12 and the thermoelectric device 1000 to store cold air formed in the thermoelectric device 1000 . The cold air stored in the heat storage tank 15 is applied to the purified water tank 12 to cool the water contained in the purified water tank 120 .

The heat storage tank 15 may be in surface contact with the purified water tank 12 so that cold air can be smoothly transmitted.

As described above, the thermoelectric device 1000 has a heat absorbing surface and a heat generating surface, and one side is cooled and the other side is heated by the movement of electrons on the P-type semiconductor and the N-type semiconductor.

Here, one side may be the purified water tank 12 side, and the other side may be the opposite side of the purified water tank 12 .

In addition, as described above, the thermoelectric device 1000 has excellent waterproof and dustproof performance, and improved thermal fluid performance, so that the purified water tank 12 can be efficiently cooled in the water purifier.

Hereinafter, an example in which a thermoelectric element according to an embodiment of the present invention is applied to a refrigerator will be described with reference to FIG. 18 .

18 is a block diagram of a refrigerator to which a thermoelectric element is applied according to an embodiment of the present invention.

The refrigerator includes a simon evaporating chamber cover 23 , an evaporating chamber partition wall 24 , a main evaporator 25 , a cooling fan 26 , and a thermoelectric device 1000 in the simon evaporating chamber.

The inside of the refrigerator is divided into a sim-on storage chamber and a sim-on evaporation chamber by a sim-on evaporation chamber cover 23 .

In detail, the inner space corresponding to the front of the simon evaporating chamber cover 23 may be defined as the simon storage chamber, and the inner space corresponding to the rear of the simon evaporating chamber cover 23 may be defined as the simon evaporating chamber.

A discharge grill 23a and a suction grill 23b may be respectively formed on the front surface of the sim-on evaporation chamber cover 23 .

The evaporation chamber partition wall 24 is installed at a point spaced forward from the rear wall of the inner cabinet, and partitions a space in which the deep greenhouse storage system is placed and a space in which the main evaporator 25 is placed.

The cold air cooled by the main evaporator 25 is supplied to the freezing chamber and then returned to the main evaporator.

The thermoelectric device 1000 is accommodated in the sim-on evaporator, and has a structure in which the heat absorbing surface faces the drawer assembly of the sim-on storage chamber and the heat-generating surface faces the evaporator. Therefore, it can be used to rapidly cool the food stored in the drawer assembly to an ultra-low temperature state of minus 50 degrees Celsius or less by using the endothermic phenomenon generated by the thermoelectric device 1000 .

In addition, as described above, the thermoelectric device 1000 has excellent waterproof and dustproof performance and improved thermal fluid performance, so that the drawer assembly can be efficiently cooled in the refrigerator.

The thermoelectric element according to an embodiment of the present invention may be applied to a device for power generation, a device for cooling, a device for heating, and the like. Specifically, the thermoelectric element according to an embodiment of the present invention is mainly an optical communication module, a sensor, a medical device, a measuring device, aerospace industry, a refrigerator, a chiller, a car ventilation seat, a cup holder, a washing machine, a dryer, and a wine cellar. , water purifiers, power supplies for sensors, thermopiles, and the like.

Here, as an example in which the thermoelectric element according to an embodiment of the present invention is applied to a medical device, there is a PCR (Polymerase Chain Reaction) device. PCR equipment is equipment for determining the nucleotide sequence of DNA by amplifying DNA, and it requires precise temperature control and thermal cycle. To this end, a Peltier-based thermoelectric element may be applied.

As another example in which the thermoelectric element according to an embodiment of the present invention is applied to a medical device, there is a photodetector. Here, the photodetector includes an infrared/ultraviolet detector, a charge coupled device (CCD) sensor, an X-ray detector, and a Thermoelectric Thermal Reference Source (TTRS). A Peltier-based thermoelectric element may be applied for cooling the photodetector. Accordingly, it is possible to prevent a change in wavelength, a decrease in output, and a decrease in resolution due to an increase in the temperature inside the photodetector.

As another example in which the thermoelectric element according to an embodiment of the present invention is applied to a medical device, an immunoassay field, an in vitro diagnostics field, a general temperature control and cooling system, Physical therapy fields, liquid chiller systems, blood/plasma temperature control, etc. Accordingly, precise temperature control is possible.

As another example in which the thermoelectric element according to an embodiment of the present invention is applied to a medical device, there is an artificial heart. Accordingly, power can be supplied to the artificial heart.

Examples of the thermoelectric element according to an embodiment of the present invention applied to the aerospace industry include a star tracking system, a thermal imaging camera, an infrared/ultraviolet detector, a CCD sensor, the Hubble Space Telescope, and a TTRS. Accordingly, the temperature of the image sensor may be maintained.

As another example in which the thermoelectric element according to an embodiment of the present invention is applied to the aerospace industry, there are a cooling device, a heater, a power generation device, and the like.

In addition, the thermoelectric element according to an embodiment of the present invention may be applied to power generation, cooling, and heating in other industrial fields.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that it can be done.

Claims (11)

a first substrate;
a plurality of first electrodes disposed on the first substrate;
a plurality of first solder layers disposed on the plurality of first electrodes;
a plurality of first buffer layers disposed on the plurality of first solder layers;
a plurality of thermoelectric legs disposed on the plurality of first buffer layers;
a plurality of second buffer layers disposed on the plurality of thermoelectric legs;
a plurality of second solder layers disposed on the plurality of second buffer layers;
a plurality of second electrodes disposed on the plurality of second solder layers, and
a second substrate disposed on the plurality of second electrodes;
A ratio of the heights of the plurality of thermoelectric legs to the heights of the plurality of first buffer layers and the height ratio of the plurality of thermoelectric legs to the heights of the plurality of second buffer layers are respectively 1:125 to 0.85,
The coefficients of linear expansion of the plurality of first buffer layers and the coefficients of linear expansion of the plurality of second buffer layers are greater than the coefficients of linear expansion of the plurality of thermoelectric legs,
The plurality of first buffer layers and the plurality of second buffer layers include aluminum. delete The method of claim 1,
The coefficients of linear expansion of the plurality of first buffer layers and the coefficients of linear expansion of the plurality of second buffer layers are smaller than the coefficients of linear expansion of the plurality of first solder layers and the coefficients of linear expansion of the plurality of second solder layers. According to claim 1,
A thermoelectric element, wherein a ratio of the heights of the plurality of thermoelectric legs to the heights of the plurality of first buffer layers and the height ratio of the plurality of thermoelectric legs to the heights of the plurality of second buffer layers is 1:1 to 0.375 to 0.625, respectively. delete According to claim 1,
Each of the plurality of first buffer layers and the plurality of second buffer layers includes an aluminum layer and a nickel plating layer disposed on the aluminum layer,
The nickel plating layer is disposed to face the plurality of thermoelectric legs. According to claim 1,
Widths of the plurality of first buffer layers and widths of the plurality of second buffer layers are smaller than widths of the plurality of thermoelectric legs. 8. The method of claim 7,
Each of the plurality of first buffer layers and the plurality of second buffer layers is disposed in a region spaced apart from an edge of each of the plurality of thermoelectric legs by a predetermined distance. 9. The method of claim 8,
Each of the plurality of first buffer layers and the plurality of second buffer layers is disposed in an area spaced apart from one side of each of the plurality of thermoelectric legs by a first distance and spaced apart by a second distance from the other side opposite to the one side. and the first distance and the second distance are different from each other. The method of claim 1,
Each of the plurality of first buffer layers and the plurality of second buffer layers has a height of 0.2 to 1 mm. The method of claim 1,
The plurality of thermoelectric legs is a thermoelectric element including a P-type thermoelectric leg and an N-type thermoelectric leg.

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