Patent Application
20240292755
The present application claims priority from German Application No.: 10 2023 104 908.9, filed on Feb. 28, 2023, the content of which is incorporated herein by reference in its entirety.
The present invention refers to thermoelectric elements and methods of their manufacturing. These elements employ single layers of thermoelectric materials, p-n junctions, or p-i-n junctions. The invention further refers to thermoelectric modules employing the thermoelectric elements and methods of manufacturing such thermoelectric modules. The thermoelectric elements and modules can be used for generating electricity or for heat transfer.
The thermoelectric effect was already discovered and described by Peltier and Seebeck in the 19th century. It was found that a relationship exists between the heat currents and electrical currents flowing through combinations of different metals, alloys or semiconductors (also referred to hereinafter as “thermoelectric materials”). On the one hand, a heat flow can create an electrical potential between the hotter and colder end of the thermoelectric material, and this can be exploited in the form of a current flow through a closed electrical circuit (Seebeck effect, thermoelectric generator). On the other hand, the application of an electrical potential to such material leads not only to a current flow but also to a heat flow, i.e. one electrical contact face becomes hotter and the other becomes cooler (Peltier effect, Peltier cooler).
Thermoelectric elements employ as usual thermoelectric legs boded to electrodes. Each of these legs is made of a thermoelectric material having a p-type or n-type conductivity. The legs are made of thermoelectric pellets or layers. Electrodes are bonded to opposite sides of a thermoelectric pellet, whereas one side of a structured thermoelectric layer is in contact with metal electrodes on a substrate and the substrate itself. The pellet-based thermoelectric elements are usually manufactured as follows: first pellets of thermoelectric materials of different conductivity types are prepared, afterwards opposite sides of the pellets are metallised for facilitating soldering or brazing, and after metallisation the pellets are affixed to metal electrodes by soldering or brazing. The layer-based thermoelectric elements are usually manufactured as follows: first a metallisation layer is deposited and structured on a dielectric substrate to form metal electrodes, afterwards a first thermoelectric layer of a first conductivity type (e.g., p-type) is deposited and structured on the substrate to form thermoelectric legs of the first conductivity type, and after the deposition and structuring of the first thermoelectric layer a second thermoelectric layer of a second conductivity type (e.g., n-type) is deposited and structured on the dielectric substrate to form thermoelectric legs of the second conductivity type.
Thermoelectric elements can also be implemented using p-n junctions. Such a thermoelectric element with a p-n junction is known from EP 1 287 566 B1. In this thermoelectric element a higher efficiency is achieved in comparison with conventional thermoelectric elements. In the thermoelectric element disclosed in EP 1 287 566 B1 the p-n junction is formed essentially over the entire extension of the n and p layer, whereby a temperature gradient is applied along the p-n junction interface. This results in a temperature difference along this elongated p-n junction between two ends of the p-n layer stack. The thermoelectric element is selectively contacted at the n and p layers. This can be done either by alloying the contacts and the associated p-n junctions or by directly contacting the n- and p-layer. To connect several thermoelectric elements to form a generator, they are connected in series by cross-connected lines. Thermally, the individual thermoelectric elements of the generator are connected in parallel.
Layer-based thermoelectric legs have lower cross-sections for heat transport in comparison with pellet-based thermoelectric legs. As a result, thermoelectric generators employing such legs can be effective when harvesting electricity from low-density heat sources which can have large areas. In turn Peltier coolers employing such legs can be used for cooling large surfaces. Put another way: thermoelectric elements employing pellet-based thermoelectric legs may require heat concentrators when used for these purposes.
The layer-based thermoelectric electricity generators and Peltier based heat transfer modules have their limitations due to parasitic heat flow via substrates. Moreover, widely industrialized layer deposition techniques like physical vapour deposition (PVD) or chemical vapour deposition (CVD) may be not optimal for deposition of thermoelectric layers having a thickness more than 1 μm, particularly when a high manufacturing throughput is required. Such a thickness limitation may result in large lateral dimensions of a layer-based thermoelectric leg when a relatively large cross-section of a layer-shaped thermoelectric leg is required. This can be illustrated on the following example. A typical cross-section of a thermoelectric pellet is 10 mm2. For a back of the envelop estimation it is assumed that 1 mm2 is a minimum pellet cross-section which manufacturing can be industrialized. Based on this assumption thermoelectric elements having cross-sections of less than 1 mm2 must be manufactured using thermoelectric layers. A limitation of the layer thickness to 1 μm results in a 1000 mm wide thermoelectric element, when a 1 mm2 cross-section of a thermoelectric leg is required. However, utilization of a 100 μm thick layer results in a 10 mm wide thermoelectric element. The latter option is obviously much more suitable for industrialization.
Based on these considerations, the technical objective of the invention is to develop a thermoelectric element and a method of manufacturing thereof, wherein the thermoelectric element is manufacturable using industrialised processes in an inexpensive way. The thermoelectric element is suitable for series connection in a thermoelectric electricity generator and/or a heat transfer module. The technical objective of the invention is further to develop such a generator and a heat transfer module and methods of manufacturing thereof.
The proposed solution is described herein using the following terms having the meanings formulated below:
The solution is based on an idea of forming a thermoelectric film on a metal foil. Afterwards a gap is formed in the metal foil to form a pair of metal foil electrodes. One of the metal foil electrodes is arranged for a thermal coupling to a heat sink and another one is arranged for a thermal coupling to a heat source. A voltage generated by this thermoelectric element, when heat flows from the heat source to the heat sink via the thermoelectric film, is tapped from the metal foil electrodes. The thermoelectric element operates as a Peltier element when an electrical current passes between the metal foil electrodes via the thermoelectric film. Such a topology of the thermoelectric element does not include a dielectric substrate, which is used in state-of-the-art thermoelectric elements for supporting metal electrode layers and thermoelectric legs made of thermoelectric films. The absence of the substrate simplifies the design of thermoelectric elements because there is no need to consider a difference between a thermal expansion coefficient (TEC) of a material of the substrate and TECs of materials of the thermoelectric leg and metal electrodes. Another advantage of the absence of the substrate is, that utilisation of the substrate for supporting a thermoelectric leg causes a parasitic heat flow via the substrate that bypasses the thermoelectric leg. Utilisation of the flexible metal foil for the metal foil electrodes facilitates integration of multiple thermoelectric elements over big areas, because a thermal expansion caused by heating is compensated by the flexibility the metal foil electrodes. Metal foil electrodes are also used for electrical serial connection of thermoelectric elements, to manufacture thermoelectric generators or Peltier coolers.
The forming of the thermoelectric films on the metal foils provides for another advantage such as utilization of powder compaction for the forming of the entire thermoelectric films or at least their bulk layers. Moreover, this “planar” approach does not have limitations typical for film-based or layer-based devices, like step-coverage, when a film or a layer is formed on a not flat surface. For instance, it is desirable to have a thickness of a thermoelectric film deposited by sputtering in a gap between metallisation pads on a flat substrate comparable to a thickness of the metallisation pads. When this criterion is not complied with such a thermoelectric element may have poor thermal and/or electrical contacts between the metallisation pads and the thermoelectric film.
As described herein the topology of the thermoelectric element facilitates advanced interface engineering between metal electrodes and thermoelectric legs. In particular, the interface can be a contamination-free interface, and/or an interface with specifically engineered properties, like work function and/or electrical and/or thermal resistance. Such an interface engineering can be implemented by depositing (e.g., sputter deposition) of various coating layers on the metal foil without exposing the metal foil to a contaminating and/or oxidizing environment. Such an approach may also include depositing (e.g., sputter deposition) a layer of a thermoelectric material on the coating layer of the metal foil without exposing the metal foil to a contaminating and/or oxidizing environment. The forming of the film of the thermoelectric material on the metal foil can comprise said deposition of the thermoelectric material. The forming of the film of the dielectric material can be continued using another method (e.g., powder compaction of a powder of the same or different thermoelectric material), when a desired thickness of the film of the thermoelectric material exceeds a thickness limit acceptable for industrial deposition of the layer of the thermoelectric material (e.g., about 10 μm, preferably 1 μm, for sputter deposition of Bi2Te3 based thermoelectric materials) on the coating layer of the metal foil. Such an approach can be used not only for manufacturing of high-quality interfaces between metal foil electrodes and films of thermoelectric materials but for manufacturing of high-quality interfaces between films of different thermoelectric materials. It is important to note that the thickness limit acceptable for industrial deposition like PVD or CVD is not a physical limit for film deposition as such. Films having thickness bigger than the aforementioned limit of about 10 μm can be deposited. However, this may result in an unfavourably long deposition time. On the other hand, long deposition time of thick films may be acceptable for industrialisation of so-called premium products.
The topology of the thermoelectric element employing only one thermoelectric leg of a specific conductivity type can be extended for manufacturing of thermoelectric elements employing p-n junctions. A topology of a thermoelectric element employing a p-n junction can be described as a combination of two thermoelectric elements each employing only one thermoelectric leg, wherein these thermoelectric legs have different conductivity types and contact each other, resulting in a p-n junction. Such a topology of the thermoelectric element employing the p-n junction allows utilization, without substantial modification, of manufacturing steps used for manufacturing of thermoelectric elements having only one thermoelectric leg of a specific conductivity type for manufacturing of thermoelectric elements employing p-n junctions. Put another way: a thermoelectric element employing a p-n junction and a method of manufacturing thereof can be seen as an extension of a thermoelectric element employing only one thermoelectric leg of a specific conductivity type and a method of its manufacturing. The metal foil electrodes are used for thermal coupling of the thermoelectric element employing the p-n junction to a heat source and a heat sink and for tapping voltage generated by the thermoelectric element when the latter is in operation. The metal foil electrodes are also used for electrical connection of the thermoelectric elements employing p-n junctions in series, to manufacture a thermoelectric module.
Axis directions X, Y, Z are the same in all Figures.
Like-numbered elements in
The central portion of the first thermoelectric film 101 does not necessarily arranged such that it is in the middle or centre of the thermoelectric film 101 or the thermoelectric element 10. The central portion refers rather to the function of the thermoelectric element 10, i.e., it refers to its “heart”. The central portion is used for the heat flow between the first and the second metal foil electrodes 111 and 112 and the electricity generation. The rest of the first thermoelectric film, if present, may be used for making the thermoelectric element 10 more stable mechanically or may be a result of a specific manufacturing method. The same applies when the thermoelectric element 10 is used for heat transport. The heat is transported via the central portion between the first and the second metal foil electrodes 111 and 112. The central portion is also used for passing the electrical current between the first and the second metal foil electrodes 111 and 112.
The first thermoelectric film 101 has a first side and a second side being opposite to the first one. The first and the second metal foil electrodes 111 and 112 are in direct contact with the first side of the first thermoelectric film 101. An interface between the first metal foil electrode 111 and the first thermoelectric film 101 and an interface between the second metal foil electrode 112 and the first thermoelectric film 101 are planar and disposed in the same first flat plane, which is parallel to X-Y plane in
The first and the second metal foil electrodes 111 and 112 may have coatings 121 and 122 being in direct contact with the first thermoelectric film 101 at the first and the second interfaces, respectively. In turn, the first thermoelectric film 101 may have a first contact interface layer 106 on its first side, wherein the first contact interface layer 106 is in direct contact with the first and the second metal foil electrodes 111 and 112 at the first and the second interfaces, respectively. The first contact interface layer 106 is in direct contact with the coatings 121 and 122, when these are used.
When the thermoelectric element 10 is used for electricity generation, one of the first and the second metal foil electrodes 111 and 112 is arranged for thermal coupling to a heat sink, whereas another one of the first and the second metal foil electrodes 111 and 112 is arranged for thermal coupling to a heat source. A voltage generated by the thermoelectric element 10, when the latter is in operation, is tapped from the first metal foil electrode 111 and the second metal foil electrode 112. In this regime heat flows from one of the metal foil electrodes 111 and 112 via the first thermoelectric film 101 to another one of the first and the second metal foil electrodes 111 and 112. When the thermoelectric element 10 is used for heat transfer (e.g., Peltier cooling), heat is transported from one of the first and the second metal foil electrodes 111 and 112 to another one of the first and the second metal foil electrodes 111 and 112, when electrical current passes between the first and the second metal foil electrodes 111 and 112 via the first thermoelectric film 101.
The simplicity of the construction of the thermoelectric element 10 allows to state that the thermoelectric element 10 can consist of three structural components such as the first thermoelectric film 101 and the first and the second metal foil electrodes 111 and 112. Properties of such a thermoelectric element 10 can be tuned by optimizing one or more of these three structural components 101, 111, and 112 without adding any further structural components. For instance, metal foils having specific coatings can be used for the first and the second metal foil electrodes 111 and 112. The shape of the first gap 131 can be optimized. The first thermoelectric film 101 can be formed in several steps for forming or depositing respective layers of the first thermoelectric film 101. On the other hand, utilization of only three structural components 101, 111, and 112 does not impose a limitation as such on the structure of the thermoelectric element 10. For instance, further metal foil electrodes (e.g., 113 and 114) can be used in the thermoelectric element 10. Those skilled in the art will readily understand, that utilization of only three structural components 101, 111, and 112 does not limit design optimization of the thermoelectric element 10 as such.
A thickness of the metal foil used for the first and the second metal foil electrodes 111 and 112 can be selected such a thermal conductivity of the first and the second metal foil electrodes 111 and 112 is at least 10 times higher, preferably at least 20 times higher, than a thermal conductivity of the thermoelectric leg. An optional requirement of sufficient flexibility of the first and the second metal foil electrodes 111 and 112 can be used for determining an upper limit for the thickness of metal foil used for the first and the second metal foil electrodes 111 and 112. In addition, the first thermoelectric film 101 can be formed and/or structured such that distal end portions of the first and the second metal foil electrodes 111 and 112 are devoid of the material of the first thermoelectric film 101, wherein the distal end portions are distal to the first gap 131 (
The thermoelectric element 10 may further comprise a third metal foil electrode 113 and a fourth metal foil electrode 114, each being in direct contact with the second side of the first thermoelectric film 101 (
The third and the fourth metal foil electrodes 113 and 114 can be made of a metal foil which is selected in accordance with the criteria formulated for the metal foil used for the first and the second metal foil electrodes 111 and 112. Analogous to the first and the second metal foil electrodes 111 and 112, the first thermoelectric film 101 can be formed such that distal end portions of the third and the fourth metal foil electrodes 113 and 114 are devoid of the material of the first thermoelectric film 101, wherein the distal end portions are distal to the second gap 132 (
A direct mechanical and/or electrical connection (e.g., by soldering or brazing) may be provided between the distal end portions of the first and the third metal foil electrodes 111 and 113 when they devoid of the material the first thermoelectric film 101. A direct mechanical and/or electrical connection (e.g., by soldering or brazing) may be provided between the distal end portions of the second and the fourth metal foil electrodes 112 and 114 when they devoid of the material the first thermoelectric film 101.
In the thermoelectric element 10 the first and the third metal foil electrodes 111 and 113 have the same function and the second and the fourth metal foil electrodes 112 and 114 have the same function as well. The same function means thermal and electrical coupling. For instance, the first and the third metal foil electrodes 111 and 113 can be arranged for thermal coupling to a heat sink and the second and the fourth metal foil electrodes 112 and 114 can be arranged for thermal coupling to a heat source, whereas a voltage generated by the thermoelectric element 10, when the latter is in operation, is tapped from at least one of the first and the third metal foil electrodes 111 and 113 and at least one of the second and the fourth metal foil electrodes 112 and 114. Utilization of the first metal foil electrode 111 in parallel with the third metal foil electrode 113 for thermal and/or electrical transport may facilitate thermal coupling of the first thermoelectric film 101 and/or reduce a resistance of an electrical contact to the first thermoelectric film 101. Utilization of the second metal foil electrode 112 in parallel with the fourth metal foil electrode 114 for thermal and/or electrical transport may result for the same improvements.
In each of the thermoelectric elements 10 and 20, the first and the second metal foil electrodes 111 and 112 are separated by the first gap 131 and the third and the fourth metal electrodes 113 and 114 are separated by the second gap 132. The metal foil electrodes 111-114 and the gaps 131 and 132 are positioned in the same way relative to each other in both thermoelectric elements 10 and 20. In the thermoelectric elements 10 and 20 the interface between the first metal foil electrode 111 and the first thermoelectric film 101 at the first side of the first thermoelectric film 101 and the interface between the second metal foil electrode 112 and the first thermoelectric film 101 at the first side of the first thermoelectric film 101 are planar and disposed in the same first flat plane, which is parallel to X-Y plane in
Analogous to the thermoelectric element 10 with four metal foil electrodes 111-114, the first thermoelectric layer 101 or its central portion bridging the gap 131 between the first and the second metal foil electrodes 111 and 112 may be planar and/or the second thermoelectric film 102 or its central portion bridging the gap 132 between the third and the fourth metal foil electrodes 113 and 114 may be planar in the thermoelectric element 20. The first thermoelectric film 101 or its central portion and the second thermoelectric film 102 or its central portion may have planar surfaces constituting the planar interface of the p-n or p-i-n junction. This interface is parallel to the first and the third flat planes and disposed between these planes. The later criterium is more relaxed in comparison to the criterium referring to the planar films or their portions.
The metal foil electrodes 111-114 can be implemented in the same way in both thermoelectric elements 10 and 20. This formulation does not exclude an optional requirement related to utilization of different coatings of metal foil electrodes specific for respective conductivity types of thermoelectric films. For instance, all metal foil electrodes 111-114 in the thermoelectric element 10 may have first coatings 121-124 required for a thermoelectric film 101 having p-type conductivity, whereas second coatings 121-124 are required when the thermoelectric element 10 employs a thermoelectric film 101 having n-type conductivity. In contrast the first and the second coatings are used in the thermoelectric element 20 employing the thermoelectric film 101 having p-type conductivity and the thermoelectric film 102 having n-type conductivity. The first coatings 121 and 122 are used for the first and the second metal foil electrodes 111 and 112, because they contact the thermoelectric film 101 having p-type conductivity, whereas the second coatings 123 and 124 are used for the third and the fourth metal foil electrodes 113 and 114, because they contact the thermoelectric film 102 having n-type conductivity.
For the same reasons as mentioned above the thermoelectric films 101 and 102 used in the thermoelectric element 20 can be formed and/or structured in the same way in the thermoelectric film 101 in the thermoelectric element 10. Distal end portions of the metal foil electrodes 111-114 can be devoid of the first and the second thermoelectric films 101 and 102. Alternatively distal portions of the first thermoelectric film 101 arranged on the distal end portions of the first and the second metal foil electrodes 111 and 112 may be thinner, preferably at least 10 times, than the central portion of the first thermoelectric film 101 bridging the first gap 131 (
In the thermoelectric element 20, the first metal foil electrode 111 and/or the third metal foil electrode 113 are arranged for thermal coupling to a heat sink, whereas the second metal foil electrode 112 and/or the fourth metal foil electrode 114 are arranged for thermal coupling to a heat source. A voltage generated by the thermoelectric element 20, when in operation for electricity generation, is tapped from the first metal foil electrode 111 and the third metal foil electrode 113.
Thermoelectric materials of different conductivity types can have different electrical and/or thermal conductivities. As usual n-type thermoelectric materials have higher electrical conductivity and/or thermal conductivity than p-type thermoelectric materials. When required, such a disparity is compensated by adapting of cross-sections of thermoelectric legs in the thermoelectric elements 10 employing single thermoelectric films and by adapting thickness of the first and/or the second thermoelectric films 101 and 102 in the thermoelectric elements 20 employing p-n junctions. A cross-section of a thermoelectric leg in the thermoelectric element 10 can be adapted by varying a width (Y direction in
Thermoelectric materials used herein can be inorganic, organic, metal-organic materials, or mixtures of thereof.
Non-limiting examples of inorganic thermoelectric materials are the following. Bi2 Te3-based thermoelectric materials (e.g., n-type Cu0.01Bi2 Te2.7Se0.35 or Bi2Te2.7Se0.3; p-type BixSb2-xTe3) and metal foil electrodes (e.g., structured copper foils coated (e.g., plated) by nickel or cobalt) can be used in thermoelectric elements operating in a temperature rage below 400 degrees Celsius, preferably below 300 degrees Celsius. Preferred coatings of metal foil electrodes for Bi2Te3-based thermoelectric materials of n-type are (Bi2 Te2.7Se0.3)0.99(SbI3)0.01, NiSe2, Co, NiFeInS, Sb, Fe0.85Cr0.15, TiN or Ti. Preferred coating for metal foil electrodes for Bi2Te3-based thermoelectric materials of p-type is Ni, however the preferred coatings for Bi2Te3-based thermoelectric materials of n-type are also usable for p-type. CoSb3-based skutterudite thermoelectric materials (e.g., n-type Ba0.08La0.05Yb0.04CO4Sb12 and p-type Ce0.45Nd0.45Fe3.5Co0.5Sb12), cold side metal foil electrodes (e.g., structured copper foil coated by Ti, Ga—Sn alloy, Ag—Cu—Zn alloy, or Mo Mo, Cr—Fe—Co alloy or Cr—Fe—Ni alloy), and hot side metal foil electrodes (e.g., structured molybdenum foils or structured Mo—Cu alloy or Co—Si alloy foils coated by Ti, Ga—Sn alloy, Ag—Cu—Zn alloy, Mo, Cr—Fe—Co alloy or Cr—Fe—Ni alloy) can be used in thermoelectric elements operating in a temperature range from 20 to 700 degrees Celsius, preferably from 70 to 550 degrees Celsius. Half-Heusler (HH) alloy-based thermoelectric materials (e.g., n-type XIVNiSn; p-type XIVCoSb, XVFeSb, ZrCoBi, where Xiv one or more of Ti, Zr, or Hf, and Xy one or more V, Nb, Ta), cold side metal foil electrodes (e.g., structured copper foils coated by Mo), and hot side metal foil electrodes (e.g., structured molybdenum or Mo—Fe alloy foils or structured Mo—Cu alloy or Co—Si alloy foils coated by Mo or Ti) can be used in thermoelectric elements operating in a temperature range from 200 to 1000 degrees Celsius, preferably from 300 to 900 degrees Celsius. SiGe-based thermoelectric materials and metal foil electrodes (e.g., structured foils of molybdenum or tungsten coated as an option by graphite) can be used in thermoelectric elements operating in a temperature range above 600 degrees Celsius, preferably above 750 degrees Celsius.
Non-limiting examples of organic thermoelectric materials are the following: poly(3,4-ethylenedioxy thiophene) polystyrene sulfonate (PEDOT:PSS), polyaniline (PANI), PEDOT-based nanocomposites comprising single/multi-wall carbon nanotubes, graphene, or carbon black, poly(3,4-ethylenedioxythiophene).
Non-limiting examples of metal-organic thermoelectric materials are n and p-type polymers containing 1,1,2,2-ethenetetrathiolate (ett) linking bridge: poly[Ax(M-ett)] (A=tetradecyltrimethyl ammonium, tetrabutyl ammonium, Na+, K+, Ni2+, Cu2+, M=Ni, Cu).
Non-limiting examples of organic-inorganic mixture thermoelectric materials are PEDOT-based nanocomposites with inorganic loadings like GeO2 nanoparticles, MoS2 nanosheets, or BN nanosheets.
As mentioned above, the metal foil electrodes 111-114 may have coatings 121-124, respectively, as illustrated in
The thermoelectric film (e.g., 101, 102) used in the thermoelectric element (e.g., 10, 20) may comprise several layers having different chemical compositions. The “classical” formalism used in semiconductor devices, based on the dopant concentration in high quality semiconductor layers, may be quite difficult to apply to thermoelectric materials because the doping efficiency in these materials is quite low. Unlike high quality Si crystals having a few dopant atoms per million of Si atoms thermoelectric materials have 1 dopant atom per 1000 or even 100 atoms of the material. In this respect it may be more practical to characterise thermoelectric films and their layers by bulk properties of materials used for their manufacturing. The bulk properties of a specific material comprise its chemical composition and charge carrier concentration, which can be measured from Hall effect. For instance, Se and Sb used for tuning electrical and/or thermal conductivity of Bi2Te3-based thermoelectric materials are denoted in chemical compositions of n-type and p-type Bi2Te3-based thermoelectric materials. Such an approach is more universal since it is applicable for a broad spectrum of thermoelectric materials. This does not necessarily mean that the “classical” formalism used in semiconductor devices employing high quality semiconductor layers is useless for characterisation of the thermoelectric films. It may be appropriate for characterisation of SiGe-based thermoelectric films. Such films can be deposited using CVD techniques, which are very well developed in the semiconductor industry.
The thermoelectric film (e.g., 101 or 102) of the thermoelectric element (e.g., 10, 20) may comprise a bulk layer and an interface layer (e.g., 103, 104, 106, 107, 108) being in direct contact with one of the opposite sides of the bulk layer. The thermoelectric film may further comprise another interface layer being in direct contact with another one of the opposite sides of the bulk layer. The opposite sides of the bulk layer are preferably parallel to X-Y plane. The bulk layer is preferably a planar layer. The bulk layer is preferably 10 times thicker than the interface layer of the same thermoelectric film. The same is valid for the other interface layer, if two interface layers are used in the thermoelectric film. A contact interface layer (e.g., 106, 107, 108) being in direct contact with a bilk layer and a metal foil electrode (e.g., 111, 112, 113, 114) may serve a purpose of optimisation of a contact interface between the metal foil electrode and a thermoelectric film comprising the interface layer and a bulk layer, whereas a junction interface layer (e.g., 103, 104) being in direct contact with a thermoelectric film of a p-n or p-i-n junction and a bulk layer of another thermoelectric film of the p-n or p-i-n junction may serve a purpose of optimisation of junction interfaces (e.g., 105) between these thermoelectric films constituting the p-n or p-i-n junction. For the sake of consistent narrative: if a thermoelectric film (e.g., 101 or 102) does not have a contact interface layer then its bulk layer is in direct contact with the metal foil electrodes (e.g., a 111 and 112, or 113 and 114); if a thermoelectric film (e.g., 101 or 102) does not have a junction interface layer then its bulk layer is in direct contact with another thermoelectric film (e.g., 102 or 101).
In particular, the first and/or the second thermoelectric films 101 and/or 102 may have contact interface layers 106, 107, 108 being in direct contact with the respective metal foil electrodes 111-114 (
In the thermoelectric elements 10 and 20 the first thermoelectric film 101 may have the first contact interface layer 106 covering its entire first side as depicted in
In the thermoelectric element 10 the first thermoelectric film 101 may have another first contact interface layer 107 covering its entire second side as depicted in
In the thermoelectric element 20 the second thermoelectric film 102 may have a second contact interface layer 108 covering its entire second side as depicted in
In the thermoelectric element 20 the first thermoelectric film 101 may comprise a first junction interface layer 103 between the second thermoelectric film 102 and the bulk layer of the first thermoelectric film 101. The first junction interface layer 103 is made of a thermoelectric material having a lower charge carrier concentration than a thermoelectric material used for the bulk layer of the first thermoelectric film 101. These materials have the same conductivity type and belong to the same group of thermoelectric materials, e.g. a group of Bi2 Te3-based thermoelectric materials. Preferably these materials have similar chemical composition, e.g., their chemical compositions differ by only one or two chemical elements, more preferably by only one chemical element. For instance, a bulk layer of a thermoelectric film can be made of Cu0.01Bi2Te2.7Se0.35 or Bi2Te2.7Se0.3, whereas a junction interface layer of the thermoelectric film can be made of Bi2Te3. Even more preferably these materials are made of the same chemical elements and differ from each other by quantities (e.g., at. %) of these chemical elements. A stack of layers having different chemical compositions may be used instead of the first junction interface layer 103. Such an implementation may be of advantage when a gradual change of thermoelectric film properties (e.g., charge carrier concentration) is required in a direction perpendicular to the junction interface 105 (Z direction
The second thermoelectric film 102 may comprise a second junction interface layer 104 between the first thermoelectric film 101 and the bulk layer of the second thermoelectric film 102. Analogously to the first junction interface layer 103 the second junction interface layer 104 is made of a thermoelectric material having a lower charge carrier concentration than a thermoelectric material used for the bulk layer of the second thermoelectric film 102. These materials have the same conductivity type and belong to the same group of thermoelectric materials, e.g. a group of Bi2Te3-based thermoelectric materials. Preferably these materials have similar chemical composition, e.g., their chemical compositions differ by only two chemical elements, more preferably by only one chemical element. Even more preferably these materials are made of the same chemical elements and differ from each other by quantities of these chemical elements. A stack of layers having different chemical compositions may be used instead of the second junction interface layer 104. Such an implementation may be of advantage when a gradual change of thermoelectric film properties (e.g., charge carrier concentration) is required in a direction perpendicular to the junction interface 105 (the direction opposite to Z direction
Utilisation of the one or both junction interface layers 103 and 104 enables optimisation of the p-n interface 105, as mentioned above, but also implementation of a p-i-n junction, when the one or both junction interface layers 103 and 104 are made of thermoelectric materials having sufficiently low charge carrier concentration. The low charge carrier concentration is preferably less than 1023 m−3, more preferably less than 1022 m−3 more preferably less than 1021 m−3. Utilisation of one or both contact interface layers 106 and 108 enables optimisation of p-n junction in particular implementation of junctions like n+n-pp+, n+n-p, and n-pp+. Utilization of the second junction interface layer 104 and the second contact interface layer 108 enables optimisation of the p-n junction such that its p- or n-portion constituted by the second thermoelectric film 102 has at least three layers and each next layer in Z direction is made of a thermoelectric material having higher charge carrier concentration than a thermoelectric material used for the previous layer. The first thermoelectric film 101 can be implemented in a similar way as the second thermoelectric film 102. Utilization of the first junction interface layer 105 and the first contact interface layer 106 enables optimisation of the p-n junction such that its n- or p-portion constituted by the first thermoelectric film 101 has at least three layers and each next layer in Z direction is made of a thermoelectric material having lower charge carrier concentration than a thermoelectric material used for the previous layer. As alternative or in addition, the properties of the first and/or the second thermoelectric films 101 and/or 102, in particular charge the carrier concentration in Z direction, may be further optimised by using stacks of layers instead of the respective bulk layers, wherein each layer of the stack is formed in a respective process and/or using respective material.
Moreover, utilisation of the junction interface layers 103 and 104 may serve a purpose of creating a contamination-free and/or low defect density interface 105 between the first and the second thermoelectric films 101 and 102. The junction interface layers 103 and 104 can be consecutively deposited without exposing a surface of one of the junction interface layers after its deposition to a contaminating environment before another one of the junction interface layers is deposited.
The layer-wise approach described above does not exclude implementation of thermoelectric films or layers having dopant concentration gradients or gradients of chemical elements altering a chemical composition such that a charge carrier density increases of decreases in a direction of the gradient. For instance, the entire thermoelectric film 101 or its junction interface layer 103 at the interface 105 can have a dopant concentration gradient in a negative Z direction, i.e., an increase in dopant concentration in a direction from the interface 105 towards the first side of the thermoelectric film 105. As alternative or in addition, the entire thermoelectric film 102 or its interface layer 103 at the interface 105 can have a dopant concentration gradient in a positive Z direction, i.e. an increase in dopant concentration in a direction from the interface 105 towards the second side of the thermoelectric film 102. Such thermoelectric films or layers can be manufactured by chemical vapor deposition (CVD) of a SiGe-based thermoelectric layer, wherein dopant precursors like phosphine or diborane are tuned during the deposition process such that the dopant concentration increases or increases throughout the layer growth. Such an approach may be of advantage for making p-n or p-i-n junctions with required interface properties. Another option for implementation the dopant concentration gradients or the gradients of the chemical elements in the first and/or the second thermoelectric films 101 and 102 is utilization of one or more coatings 121-124 comprising layers which act as sources of drive-in chemical element or elements which upon thermally activated diffusion are incorporated in the adjacent thermoelectric film 101 or 102 and thereby form the contact interface layers 106, 107 or 108 or alter their composition, when they were formed before the drive-in diffusion. Those skilled in the art will readily understand, that the option related to the CVD deposition and the option related to the drive-in diffusion option are compatible with each other and with other methods of forming films and layers described herein.
The thermoelectric elements 10 and 20 comprise two types of “building blocks” such as metal foil electrodes (e.g., 111, 112, 113, or 114) and thermoelectric films. The concept of the metal foil electrodes having a preferable thickness of at least 10 μm and the concept of the thermoelectric films having a preferable thickness of at least 10 μm have one important similarity. The metal foil electrodes and thermoelectric films have thick bulk portions preferably at least 10 μm thick, such as bulk layers of the thermoelectric films and metal foils of the metal foil electrodes, and thin portions such as coatings of the metal foils and the interface layers of the thermoelectric film. In contrast to the bulk portions, the coatings and the interface layers are preferably thinner than 1 μm. The interface layers 106-108 and the coatings 121-124 or at least their layers adjoining each other can be deposited by one or more appropriate deposition techniques like PVD or CVD, which are very well industrialised for deposition of high-quality layers of a broad spectrum of materials. Moreover, PVD and CVD technologies enable in-situ deposition of several layers, i.e. without breaking vacuum and/or exposing individual layers to a contaminating environment (e.g., air). This is of advantage for making high-quality interfaces between adjacent layers. PVD (in particular, sputter deposition) and CVD may provide high throughput and cost-effective operation when deposition of layers thinner than 1 μm is required. PVD and CVD are rarely used when deposition of layers, particularly thermoelectric layers, thicker than 10 μm is required. This deficiency is bridged by using thick metal or metal alloy foils as ingots for metal foil electrodes. Manufacturing of these foils is also very well industrialized. The bulk layers of the thermoelectric films are formed herein by powder compaction. Thickness of the bulk layer formed by powder compaction may be at least 10 μm, preferably at least 25 μm, more preferably at least 50 μm. Details of this process are discussed further.
The first and the second gaps 131 and 132 can be a slit having various shapes such as a rectangular slit, a meander-shaped slit, a sawtooth-shaped slit (triangular tooth-shaped slit), or a wave-shaped slit (e.g., a sinusoidal or cycloidal wave-shaped slit). The last three arrangements of the slit provide for an unfolded length of a slit being bigger than the width of the thermoelectric element 10 or 20 in Y direction (
For ease of reference, the thermoelectric elements 10 comprising the first thermoelectric films 101 having p-type conductivity are referred to as p-type thermoelectric elements 10 and the thermoelectric elements 10 comprising the first thermoelectric films 101 having n-type conductivity are referred to as n-type thermoelectric elements 10. The p-type and the n-type thermoelectric elements 10 can be arranged electrically in series in a thermoelectric module such that a series of the first thermoelectric films 101, which alternate in conductivity type, is formed. As a result, a voltage generated by the series of the alternating p-type and n-type thermoelectric elements 10 is a sum of voltages generated by the individual p-type and n-type thermoelectric elements 10. The serial electrical connection of the p-type and the n-type thermoelectric elements 10 is implemented using their first and second metal foil electrodes 111 and 112. The first metal foil electrodes 111 of the p-type and the n-type thermoelectric elements 10 can be arranged for thermal coupling to a heat sink. The second metal foil electrodes 112 of the p-type and the n-type thermoelectric elements 10 can be arranged for thermal coupling to a heat source. For instance, a p-type thermoelectric element 10 has its first metal foil electrode 111 electrically connected to a first metal foil electrode 111 of an n-type thermoelectric element 10 being in series immediately before said p-type thermoelectric element 10, and its second metal foil electrode 112 electrically connected to a second metal foil electrode 112 of another n-type thermoelectric element 10 being in series immediately after said p-type thermoelectric element 10, wherein said first metal foil electrodes 111 are arranged for thermal coupling to a heat sink and said second metal foil electrodes 112 are arranged for thermal coupling to a heat source. The electrical connections between pairs of the first metal foil electrodes 111 and pairs of the second metal foil electrodes 112 are implemented using only metallic conductors. A voltage generated by the thermoelectric module, when the first metal foil electrodes 111 are coupled to a heat sink and the second metal foil electrodes are coupled to a heat source 112, can be tapped from a metal foil electrode 111 or 112 of a first in series thermoelectric element 10 and a metal foil electrode 112 or 111 of a thermoelectric element 10 being the last in series, wherein said metal foil electrodes used for the voltage tapping are not used for direct electrical connection to metal foil electrodes of other thermoelectric elements 10 in the series of thermoelectric elements 10. The thermoelectric module is manufactured by electrically connecting the first metal foil electrodes and the second metal foil electrodes of the p-type and n-type thermoelectric elements 10 such that an alternating series of the first thermoelectric films having n-type conductivity and the first thermoelectric films having p-type conductivity is formed.
The thermoelectric elements 10 employing single first thermoelectric films 101 and the thermoelectric module employing these thermoelectric elements 10 can be used for heat transfer (e.g., as Peltier coolers) from a heat source (e.g., an object to be cooled) to a heat sink. In this case metal foil electrodes used for tapping the generated thermoelectric voltage are used for connecting a current source to pass a current through the thermoelectric element 10 or the series of the thermoelectric elements 10. The first metal foil electrodes 111 of the p-type and the n-type thermoelectric elements 10 are arranged for thermal coupling to a heat sink and the second metal foil electrodes 112 of the p-type and the n-type thermoelectric elements are arranged for thermal coupling to a heat source (e.g., an object to be cooled).
As mentioned above, the p-type and the n-type thermoelectric elements 10 may comprise the third and the fourth metal foil electrodes 113 and 114. The third metal foil electrodes 113 can be used in parallel with the first metal electrodes 111 for thermal coupling and/or electrical connection of the thermoelectric elements 10 and the fourth metal foil electrodes 114 can be used in parallel with the second metal electrodes 112 for thermal coupling and/or electrical connection of the thermoelectric elements 10 in the thermoelectric module for facilitating electrical and/or heat transport for both applications, i.e. electricity generation and heat transfer.
The thermoelectric elements 20 can be arranged electrically in series in a thermoelectric module such that a series of p-n or p-i-n junctions is formed, wherein the thermoelectric films of different conductivity types are alternated in the series of p-n or p-i-n junctions. As a result, a voltage generated by the series of p-n or p-i-n junctions is a sum of voltages generated by the individual thermoelectric elements. The serial electrical connection of the thermoelectric elements is implemented using the first and the third metal foil electrodes arranged 111 and 113 for thermal coupling to a heat sink. As a result, an alternating series of the first and the second thermoelectric films 101 and 102 is formed.
The electrical connection of any thermoelectric element 20 except the first and the last ones in the series is defined as follows: a thermoelectric element 20 has a first metal foil electrode 111 electrically connected to a third metal foil electrode 113 of another thermoelectric element 10 being in series immediately after said thermoelectric element, and a third metal foil electrode 113 electrically connected to a first metal foil electrode 111 of yet another thermoelectric element 20 being in series immediately before said thermoelectric element 20, wherein the electrical connections between the first and the third metal foil electrodes 111 and 113 of the adjacent in series thermoelectric elements 20 is implemented using only metallic conductors. A voltage generated by the thermoelectric module, when the first and/or the third metal foil electrodes are coupled to a heat sink and the second and/or the fourth metal foil electrodes are coupled to a heat source, is be tapped from a third metal foil electrode 113 of the thermoelectric element 20 being the first one in series and a first metal foil electrode 111 of the thermoelectric element 20 being the last one in series. The first metal foil electrode 111 and the third metal foil electrode 113 used for voltage tapping do not have direct electrical connections with any other metal foil electrodes 111 or 113 in the thermoelectric module. This thermoelectric module is manufactured by electrically connecting the first metal foil electrodes 111 with the third metal foil electrodes 113 of the thermoelectric elements 20 such that an alternating series of the first and the second thermoelectric films 101 and 102 is formed.
The electrical connections can be manufactured by soldering or brazing of the metal foil electrodes together or to interconnect elements. An interconnect element can be a metal wire, a metal bar, a metal stripe, or a combination thereof. The interconnect element may be or further comprise a dielectric substrate with a least one metallisation pad. The interconnect elements may be made of the same materials as used in the thermoelectric elements 10 or 20. Utilisation of the same materials in the interconnect elements and the thermoelectric elements 10 or 20 may be of advantage, because these elements exhibit substantially similar expansion at elevated temperature, when the thermoelectric module is in operation. The interconnect elements may provide electrical connections between the metal foil electrodes 111-114 of the thermoelectric elements 10 or 20. The interconnect elements may be adapted for thermal coupling of the thermoelectric elements 10 or 20 to a heat source or a heat sink. The interconnect elements may be further adapted for affixing together the thermoelectric elements 10 or 20.
For ease of reference, reference numerals with subscript numerals are used for description of thermoelectric modules 190 and 200 depicted in
The first interconnect element 150 comprises a dielectric substrate 151 with a row of metallisation pads 1521, . . . 152n/2, wherein n/2 is an overall number of the metallisation pads on the dielectric substrate 151. Merely for illustrative purposes only the first 1521 and the last 152n/2 metallisation pads are depicted in
The thermoelectric module 190 may further comprise another first interconnect element for connecting optional third metal foil electrodes 113 of the thermoelectric elements 101, 102, . . . 10n−1, 10n. The other fist interconnect element can be implemented and electrically connected to the third metal foil electrodes of the thermoelectric elements 101, 102, . . . 10n−1, 10n in the same way as the first interconnect element 150 is electrically connected to the first metal foil electrodes of the thermoelectric elements 101, 102, . . . 10n−1, 10n.
The second interconnect element 160 comprises a dielectric substrate 161 with a row of metallisation pads 1621, 1622, . . . 162n/2, 162n/2+1, wherein n/2+1 is an overall number of the metallisation pads on the dielectric substrate 161. Merely for illustrative purposes only the first metallisation pad 1621, a fragment of the second metallisation pad 1622, a fragment of the penultimate metallisation pad 162n/2, and the last metallisation pad 162n/2+1 are depicted in
For instance, the first in the row metallisation pad 1621 is directly electrically connected with a second metal foil electrode 1121 of an n-type thermoelectric element 101 with a first thermoelectric film 101n having n-type conductivity. The second in the row metallisation pad 1622 is directly electrically connected with a second metal foil electrode 1122 of a p-type thermoelectric element 102 and a second metal foil electrode 1123 of an n-type thermoelectric element 103 with a first thermoelectric film 101n having n-type conductivity. The n-type thermoelectric element 103 (not depicted in
The thermoelectric module 190 may further comprise another second interconnect element for connecting optional fourth metal foil electrodes 114 of the thermoelectric elements 101, 102, . . . 10n−1, 10n. The other second interconnect element can be implemented and electrically connected to the fourth metal foil electrodes of the thermoelectric elements 101, 102, . . . 10n−1, 10n in the same way as the second interconnect element 160 is electrically connected to the second metal foil electrodes of the thermoelectric elements 101, 102, . . . 10n−1, 10n.
The first and the second interconnect elements 150 and 160 provide for electrical chain of the series of thermoelectric elements 101, 102, . . . 10n−1, 10n such that the series of the first thermoelectric films 101n, 101p, . . . 101n, 101p, which alternate in conductivity type, is formed. The components of electrical chain are serially connected as follows: the first metallisation pad 1621, the second metal foil electrode 1121, the first thermoelectric film 101n of the n-type thermoelectric element 101, the first metal foil electrode 1111, the first metallisation pad 1521, the first metal foil electrode 1112, the first thermoelectric film 101p of the p-type thermoelectric element 102, the second metal foil electrode 1122, the second metallisation pad 1622, . . . the penultimate metallisation pad 162n/2, the second metal foil electrode 112n−1, the first thermoelectric film 101n of the n-type thermoelectric element 10n−1, the first metal foil electrode 111n−1, the last metallisation pad 152n/2, the first metal foil electrode 111n, the first thermoelectric film 101p of the p-type thermoelectric element 10n, the second metal foil electrode 112n, the last metallisation pad 162n/2+1. A voltage generated by the thermoelectric module 190, when the first and/or the third metal foil electrodes are coupled to a heat sink and the second and/or the fourth metal foil electrodes are coupled to a heat source, is tapped from the metallisation pads 1621 and 162n/2+1.
The thermoelectric module 190 can be used for heat transfer (e.g., as Peltier coolers) from a heat source (e.g., an object to be cooled) to a heat sink. In this case metallisation pads 1621 and 162n/2+1 used for tapping the generated thermoelectric voltage are used for connecting a current source to pass a current through the thermoelectric module 190. The first and/or the third metal foil electrodes 111 and/or 113 of the p-type and the n-type thermoelectric elements 10 are arranged for thermal coupling to a heat sink and the second and/or fourth metal foil electrodes 112 and/or 114 of the p-type and the n-type thermoelectric elements are arranged for thermal coupling to a heat source (e.g., an object to be cooled).
The first interconnect element 150 may also provide for a thermal coupling of the first metal foil electrodes 1111 . . . 111n to a heat sink. The other optional first interconnect element may also provide for a thermal coupling of the optional third metal foil electrodes 113 of the thermoelectric elements 101, 102, . . . 10n−1, 10n to a heat sink. One or both of these interconnect elements may also affix the thermoelectric elements 101, 102, . . . 10n−1, 10n in the thermoelectric module 190 thereby providing a modular structure.
The second interconnect element 160 may also provide for a thermal coupling of the second metal foil electrodes 1121 . . . 112n to a heat source. The other optional second interconnect element may also provide for a thermal coupling of the optional fourth metal foil electrodes 113 of the thermoelectric elements 101, 102, . . . 10n−1, 10n to a heat source. One or both of these interconnect elements may also affix the thermoelectric elements 101, 102, . . . 10n−1, 10n in the thermoelectric module 190 thereby providing a modular structure.
The thermoelectric module 190 can be manufactured using a soldering process or a brazing process. For instance, a surface mount soldering process can be employed for the manufacturing. A solder paste is applied to the metallisation pads 1521, . . . 152n/2 and 1621, 1622, . . . 162n/2, 162n/2+1 of the first and the second interconnect elements 150 and 160 using a stencil printing or a jet printing. In addition, the solder paste is applied to the metallisation pads of the other optional first and/or second interconnect elements when either any one or both of them are used in the thermoelectric module 190. The first and the second interconnect elements 150 and 160 are aligned relative to each other in accordance with their arrangement in the thermoelectric module 190, afterwards the thermoelectric elements 101, 102, . . . 10n−1, 10n are placed over the first and the second interconnect elements 150 and 160 such that the first metal foil electrodes 1111, 1112, . . . 111n−1, 111n of the thermoelectric elements 101, 102, . . . 10n−1, 10n to be soldered with the metallisation pads 1521, . . . 152n/2 of the first interconnect element 150 are in contact with the solder paste lumps on the respective metallisation pads 1521, . . . 152n/2 of the first interconnect element 150 and the second metal foil electrodes 1121, 1122, . . . 112n−1, 112n of the thermoelectric elements 101, 102, . . . 10n−1, 10n to be soldered with the metallisation pads 1621, 1622, . . . 162n/2, 162n/2+1 of the second interconnect element 160 are in contact with the solder paste lumps on the respective metallisation pads 1621, 1622, . . . 162n/2, 162n/2+1 of the second interconnect element 160. In the next optional step the other optional first interconnect element is placed over a stack of the first interconnect element 150 and the thermoelectric elements 101, 102, . . . 10n−1, 10n such that the third metal foil electrodes of the thermoelectric elements 101, 102, . . . 10n−1, 10n to be soldered with the metallisation pads of the other optional first interconnect element are in contact with solder paste lumps on the respective metallisation pads of the other optional first interconnect element. When the other optional second interconnect element is used, this step further comprises placing the other optional second interconnect element over the stack of the second interconnect element and the thermoelectric elements 101, 102, . . . 10n−1, 10n such that the fourth metal foil electrodes of the thermoelectric elements 101, 102, . . . 10n−1, 10n to be soldered with the metallisation pads of the other optional second interconnect element are in contact with the solder paste lumps on the respective metallisation pads of the other optional second interconnect element. In the last step the entire arrangement of at least the first interconnect element 150, the thermoelectric elements 101, 102, . . . 10n−1, 10n, and the second interconnect element 160 is processed in a solder oven at elevated temperature to produce solder connections 1701, 1702, . . . 170n−1, 170n between the metallisation pads 1521, . . . 152n/2 and the metal foil electrodes 1111, 1112, . . . 111n−1, 111n, solder connections 1801, 1802, . . . 180n−1, 180n between the metallisation pads 1621, 1622, . . . 162n/2, 162n/2+1 and the second metal foil electrodes 1121, 1122, . . . 112n−1, 112n. In addition: solder connections are made between the third metal foil electrodes and the metallisation pads of the other optional fist interconnect element, when the latter is used; and solder connections are made between the fourth metal foil electrodes and the metallisation pads of the other optional second interconnect element, when the latter is used.
The thermoelectric module 190 depicted in
The first interconnect element 280 comprises a dielectric substrate 281 with a row of metallisation pads 2821, . . . 282n/2, wherein n/2 is an overall number of the metallisation pads on the dielectric substrate 281. Merely for illustrative purposes only the first 2821 and the last 282n/2 metallisation pads are depicted in
The second interconnect element 250 comprises a dielectric substrate 251 with a row of metallisation pads 2521, 2522, . . . 252n/2, 252n/2+1, wherein n/2+1 is an overall number of the second metallisation pads on the dielectric substrate 251. Merely for illustrative purposes only the first metallisation pad 2521, a fragment of the second metallisation pad 2522, a fragment of the penultimate metallisation pad 252n/2, and the last metallisation pad 252n/2+1 are depicted in
The thermoelectric module 200 may further comprise a third interconnect element 240 and/or a fourth interconnect element 210. These interconnect elements do not provide electrical connections between metal foil electrodes of different thermoelectric elements. They may be arranged for thermal coupling of the second and the fourth metal foil electrodes of the thermoelectric elements 201 . . . 20n to a heat source and/or for affixing the thermoelectric elements 201 . . . 20n in the thermoelectric module 200 thereby providing a modular structure. The first interconnect element 280 may be arranged for a thermal coupling of the first metal foil electrodes 1111, 1113, . . . 111n−1 and the third metal foil electrodes 1132, 1134, . . . 113n to a heat sink and/or for affixing the thermoelectric elements 201 . . . 20n in the thermoelectric module 200 thereby providing a modular structure. The second interconnect element 250 may be arranged for a thermal coupling of the first metal foil electrodes 1112, 1114, . . . 111n and the third metal foil electrodes 1131, 1133, . . . 113n−3, 113n−1 to a heat sink and/or for affixing the thermoelectric elements 201 . . . 20n in the thermoelectric module 200 thereby providing a modular structure.
For instance, the third interconnect element 240 can be implemented as follows. A row of metallisation pads 2421, 2422, . . . 242n−1, 242n is arranged on a dielectric substrate 241 of the third interconnect element 240, wherein n is the overall number of the metallisation pads 2421, 2422, . . . 242n−1, 242n. Merely for illustrative purposes only the first metallisation pad 2421, the second metallisation pad 2422, the penultimate metallisation pad 242n−1, and the last metallisation pad 242n are depicted in
For instance, the fourth interconnect element 210 can be implemented as follows. A row of metallisation pads 2121, 2122, . . . 212n−1, 212n is arranged on a dielectric substrate 211 of the fourth interconnect element 210, wherein n is the overall number of the metallisation pads 2421, 2422, . . . 242n−1, 242n. Merely for illustrative purposes only the first metallisation pad 2121, the second metallisation pad 2122, the penultimate metallisation pad 212n−1, and the last metallisation pad 212n are depicted in
The first and the second interconnect elements 280 and 250 provide for electrical chain of the series of thermoelectric elements 201, 202, . . . 20n−1, 20n such that the series of p-n or p-i-n diodes are formed, wherein thermoelectric films 101 and 102 alternate in this series. In other words, a p-portion of a diode is connected to an n-portion of another diode being the next one in the series. The components of electrical chain are serially connected as follows: the first metallisation pad 2521, the third metal foil electrode 1131, the second thermoelectric film 102 of the first thermoelectric element 201, the first thermoelectric film 101 of the first thermoelectric element 201, the first metal foil electrode 1111, the first metallisation pad 2821, the third metal foil electrode 1132, the second thermoelectric film 102 of the second thermoelectric element 202, the first thermoelectric film 101 of the second thermoelectric element 202, the first metal foil electrode 1112, the second metallisation pad 2522, . . . the penultimate metallisation pad 252n/2, the third metal foil electrode 113n−1, the second thermoelectric film 102 of the penultimate thermoelectric element 20n−1, the first thermoelectric film 101 of the penultimate thermoelectric element 20n−1, the first metal foil electrode 111n−1, the last metallisation pad 282n/2, the third metal foil electrode 113n, the second thermoelectric film 102 of the last thermoelectric element 20n, the first thermoelectric film 101 of the last thermoelectric element 20n, the first metal foil electrode 111n, the last metallisation pad 252n/2+1. A voltage generated by the thermoelectric module 200, when the first and/or the third metal foil electrodes are coupled to a heat sink and the second and/or the fourth metal foil electrodes are coupled to a heat source, is tapped from the metallisation pads 2521 and 252n/2+1.
The thermoelectric module 200 can be manufactured using a soldering process or a brazing process. For instance, a surface mount soldering process can be employed for the manufacturing. A solder paste is applied to the metallisation pads 2821, . . . 282n/2 and 2521, . . . 252n/2+1 of the first and the second interconnect elements 280 and 250 using a stencil printing or a jet printing. In addition, the solder paste is applied to the metallisation pads 2421, . . . 242n and 2121, . . . 212n of the other optional third and/or fourth interconnect elements when either any one or both of them are used in the thermoelectric module 200. In the next step the thermoelectric elements 201, 202, . . . 20n−1, 20n are placed over the first interconnect element 280 such that the first and the third metal foil electrodes 1111, 1113, . . . 111n−1 and 1132, 1134, . . . 113n to be soldered with the metallisation pads 2821, . . . 282n/2 of the first interconnect element 280 are in contact with the solder paste lumps on the respective metallisation pads 2821, . . . 282n/2 of the first interconnect element 280. In case the thermoelectric module 200 comprises the third interconnect element 240, this step is performed in a different way. The first and the third interconnect elements 280 and 240 are aligned relative to each other in accordance with their arrangement in the thermoelectric module 200, afterwards the thermoelectric elements 201, 202, . . . 20n−1, 20n are placed over the first and the third interconnect elements 280 and 240 such that the first and the third metal foil electrodes 1111, 1113, . . . 111n−1 and 1132, 1134, . . . 113n to be soldered with the metallisation pads 2821, . . . 282n/2 of the first interconnect element 280 are in contact with the solder paste lumps on the respective metallisation pads 2821, . . . 282n/2 of the first interconnect element 280 and the second and the fourth metal foil electrodes 1121, 1123, . . . 112n−1 and 1142, 1144, . . . 114n to be soldered with the metallisation pads 2421, . . . 242n of the third interconnect element 240 are in contact with the solder paste lumps on the respective metallisation pads 2421, . . . 242n of the third interconnect element 240. In the next step the second interconnect element 250 is placed over a stack of the first interconnect element 280 and the thermoelectric elements 201, 202, . . . 20n−1, 20n such that the first and the third metal foil electrodes 1112, 1114, . . . 111n and 1131, 1133, . . . 113n−1 to be soldered with the metallisation pads 2521, . . . 252n/2+1 of the second interconnect element 250 are in contact with solder paste lumps on the respective metallisation pads 2521, . . . 252n/2+1 of the second interconnect element 250. When the fourth interconnect element 210 is used, this step further comprises placing the fourth interconnect element 210 over the stack of the third interconnect 240 element and the thermoelectric elements 201, 202, . . . 20n−1, 20n such that the second and the fourth metal foil electrodes 1122, 1124, . . . 112n and 1141, 1143, . . . 114n−1 to be soldered with the metallisation pads 2121, 2122, . . . 212n−1, 212n of the fourth interconnect element 210 are in contact with the solder paste lumps on the respective metallisation pads 2121, 2122, . . . 212n−1, 212n of the fourth interconnect element 210. In the last step the entire arrangement of at least the first interconnect element 280, the thermoelectric elements 201, 202, . . . 20n−1, 20n, and the second interconnect element 250 is processed in a solder oven at elevated temperature to produce solder connections 2701, 2702, . . . 270n−1, 270n between the metallisation pads 2821, . . . 282n/2 and the first and the third metal foil electrodes 1111, 1113, . . . 111n−1 and 1132, 1134, . . . 113n, solder connections 2601, 2602, . . . 260n−1, 260n between the metallisation pads 2521, 2522, . . . 252n/2, 252n/2+1 and the first and the third metal foil electrodes 1112, 1114, . . . 111n and 1131, 1133, . . . 113n−1. In addition: solder connections 2301, 2302, . . . 230n−1, 230n are made between the second and the fourth metal foil electrodes 1121, 1123, . . . 112n−1 and 1142, 1144, . . . 114n and the metallisation pads 2421, 2422, . . . 242n−1, 242n of the third interconnect element 240, when the latter is used; and solder connections 2201, 2202, . . . 220n−1, 220n are made between the second and the fourth metal foil electrodes 1122, 1124, . . . 112n and 1141, 1143, . . . 114n−1 and the metallisation pads 2121, 2122, . . . 212n−1, 212n of the fourth interconnect element 210, when the latter is used.
The thermoelectric module 200 depicted in
Brazing process may be used instead of the soldering process in the manufacturing processes of the thermoelectric modules (e.g., 190, 200). In this case a filler material is used instead of the solder paste and a furnace for brazing process is used instead of the oven. In contrast to the oven, the furnace performs the brazing process at higher temperature than the temperature of the soldering process and may provide as an option an inert atmosphere.
The first thermoelectric film 101 may be annealed. The annealing may be performed in vacuum and/or inert gas atmosphere. The annealing may be used for improving crystal structure of the first thermoelectric film 101. For instance, Bi2Te3-based thermoelectric materials can be annealed at a temperature in a range of 220-240 degrees Celsius for at least 10 hours. The annealing may be used to drive dopants from a dopant source layer of the first coating 120 into the first thermoelectric film 101 to form the first contact interface layer 106 or to change its properties, if formed prior to the annealing. For instance, a copper metal foil 110 with a nickel coating 120 functions as a drive-in source of p-type nickel dopant for a Bi2Te3-based thermoelectric layer when a stack of the metal foil 110 and the adjoining first thermoelectric film 101 is heated above 200 degrees Celsius. In case of a SiGe-based thermoelectric film 101 a coating comprising one or more of the following elements Li, Sb, P, or As can be used for drive-in n-doping and a coating comprising one or more of the following elements B, Al, or Ga can be used for drive-in p-doping.
The forming of the first thermoelectric film 101 may comprise pressure-compacting of a first powder of a first thermoelectric material on the first metal foil 110 to form the entire first thermoelectric layer 101 or its bulk layer. In the latter case the forming of the first thermoelectric layer further comprises forming a first contact interface layer 106 directly on the first metal foil 110 or its first coating 120, when the latter is used. In turn, the bulk layer of the first thermoelectric film 101 is formed directly on the first contact interface layer 106. Employing of the powder pressure-compacting for forming the first thermoelectric film 101 or its bulk layer results in the planar first thermoelectric film 101 or its planar bulk layer respectively, which have their opposite sides parallel to each other. The planar first thermoelectric film 101 or its planar bulk layer may be structured at later manufacturing steps. The first contact interface layer 106 may be formed using PVD and/or CVD. As mentioned above a stack of layers may be used instead of the first contact interface layer 106, wherein the layers of the stack are deposited using dedicated PVD and/or CVD processes and/or have different chemical compositions.
The pressure-compacted first thermoelectric film 101 is directly attached to the first metal foil 110 or its pressure-compacted bulk layer is directly attached to the first contact interface layer 106. In other words, the pressure-compacting of the first powder not only binds the particles of the first powder together, but also binds these particles to the surface of the first metal foil 110 or the surface of a top layer on the first metal foil 110. The first coating 120 may comprise an adhesion layer for facilitating the binding of the pressure-compacted powder to it. A material of the adhesion layer and a material of the first thermoelectric film or of the powder used for its forming may comprise at least one common chemical element and the atomic concentrations of this common element in these materials differ by less than 10%, preferably by less than 5%. Preferably the adhesion layer and the powder to be compacted thereon are made using the same source material. In this case, the adhesion layer and the compacted powder layer or film are made of the same chemical elements, the atomic concentrations of which differ by less than 10% in the adhesion layer and the compacted powder layer or film. For instance, the same powder can be used for the pressure-compacting on the adhesion layer and for the sputtering target used to deposit the adhesion layer. The first contact interface layer 106 may facilitate the binding of the pressure-compacted powder of the bulk layer of the first thermoelectric film 101 in a similar way. However, in contrast to the materials of the pair of the adhesion layer of the first coating 120 and the first thermoelectric film 101 the materials of the bulk and first contact interface layer may have more structural and chemical similarity, because in contrast to the adhesion layer the first contact interface layer 106 not only facilitates the adhesion of the powder of the first thermoelectric material but also has thermoelectric properties. In particular, the bulk layer and first contact interface layer 106 of the first thermoelectric film 101 may have the same crystallographic phase and/or consist of the same chemical elements, wherein the atomic concentrations of the chemical elements in these layers differ by less than 2%, preferably by less than 1%.
As mentioned above the stack of layers may be used instead of the single bulk layer. In this case each layer of the stack is formed in a separate pressure-compacting process using the first powder. Alternatively different powders of different thermoelectric materials can be used for respective layers of the stack. The latter approach can be used when the first thermoelectric film 101 or at least its bulk layer is formed using thermoelectric materials having different charge carrier concentrations.
The pressure-compacting may be performed by at least one of the following processes: hot pressing, hot pressing with ultrasonic assistance, roll-compacting, or roll-compacting with ultrasonic assistance and/or at elevated temperature. The powder or powders used for the pressure-compacting may be deoxidized and/or degassed prior to the pressure-compacting, which in turn may be performed in vacuum and/or inert gas atmosphere to prevent oxidation and/or contamination of the powder during the pressure-compacting. Degassing and/or deoxidation of the powder may be performed at an elevated temperature in vacuum and/or inert gas. Alternatively, or as an additional process step degassing and/or deoxidation may be performed at elevated temperature in a forming gas being a mixture hydrogen and nitrogen.
The powder for the pressure-compacting process of the first thermoelectric film 101, or its bulk layer, or a layer of the stack of layers used instead of the single bulk layer may be provided in dry form on the surface of the first metal foil 110 or the surface of a top layer of the first coating 120 or the first contact interface layer 106 on the first metal foil 110. The powder for the pressure-compacting process may be provided as a layer of uniform thickness, which in turn is achieved by employing a doctor blade for removal of excess powder. Alternatively, a layer of ink can be printed onto the surface of first metal foil 110 or the surface of the top layer on first metal foil 110 or the first contact interface layer 106 on the first metal foil 110. The layer of ink can be printed by inkjet or screen printing. A doctor blade may be employed for achieving uniform thickness for screen printing. The ink contains powder to be pressure-compacted in the pressure-compacting process. The first metal foil 110 with the printed ink layer thereon is annealed to remove a solvent of the ink and/or a binder of the ink from the printed ink layer. The annealing is carried out prior to the pressure-compacting as a separate process step or in the course of the deoxidizing and/or degassing of the powder to be pressure-compacted. For instance, the deoxidizing and/or degassing of the annealed printed ink layer may be performed at elevated temperature in a forming gas.
An example ink suitable for screen printing comprises particles of Bi0.5Sb1.5Te3 for p-type thermoelectric film or Bi2Te2.7Se0.3 for n-type thermoelectric film. The particles are mixed with binder solvent which consists of methyl cellulose as the binder, in a mixture of ethanol 60 wt. % and water 40 wt. %. The concentration of the methyl cellulose in the solvent is between 1.5 and 2.0 wt. %. The mass ratio between the particles and the solvent is 7:3, so methyl cellulose is 0.45-0.6 wt. % in the ink. The printed layer is annealed at 250-300° C. for 30 min to solidify the printed layer and burn of the polymeric binders. The layer is pressure-compacted with a uniaxial pressure in a range of 80-100 MPa at a temperature above 400 degrees Celsius for at least 5 min. The pressure-compacting is carried out in an inert gas atmosphere, e.g., an argon environment at atmospheric pressure with an oxygen concentration less than 100 ppm, to prevent the oxidation of the thermoelectric film.
If necessary, the surface of the first metal foil 110 or a top layer on the first metal foil 110 is cleaned prior to a formation of a layer thereon. The surface cleaning can be made for instance by inert gas plasma cleaning or by ion beam cleaning, wherein ions or atoms of an inert gas (e.g., argon) bombard the surface. Another option for cleaning the surface with can be used separately or in combination with the previous one is annealing the first metal foil 110 in a forming gas. When the specific formation method of the layer is compatible with vacuum technology, the cleaning step and the subsequent formation step can be made without breaking the vacuum and/or exposing the surface to a contaminating environment, e.g. oxygen and/or water vapour containing atmosphere. In other words, the inert environment is maintained between the surface cleaning and the layer formation. The inert environment may have partial pressures of oxygen or water vapour below 1 Pa, preferably below 0.1 Pa, more preferably below 0.01 Pa.
For instance, the first metal foil 110 can be cleaned and the first thermoelectric film 101 can be formed in an inert atmosphere on the first metal foil 110 without breaking vacuum and/or exposing the cleaned surface to a contaminating environment. This process may include forming the first coating 120 on the first metal foil 110 after its cleaning and prior to the formation of the first thermoelectric film 101 while the vacuum and/or inert atmosphere is maintained. Such an approach may be implemented by employing PVD and/or CVD processes for deposition of a layer or layers of the first coating 120 and/or the first interface layer 106, when any of these are used. In turn the first thermoelectric film 101 or its bulk layer may be formed using the first powder provided in dry form, wherein the first powder has been deoxidised and/or degassed prior to being provided on the surface of the first metal foil 110 or a layer (e.g., a layer of the first coating 120 or the first contact interface layer 106) on the first metal foil 110. Such an approach may be particularly advantageous where a low-defect density and/or contamination free interface is required not only between the first thermoelectric film 101 and the first and the second metal foil electrodes 111 and 112, but also between their individual layers.
In the above example the entire first thermoelectric film 101 and the first coating 120, if the latter is used, are formed in a vacuum and/or inert environment. This may be advantageous when the manufacturing method is implemented using a dedicated cluster tool. On the other hand, the industrialisation of the manufacturing method may be implemented using multiple independent/stand-alone tools. Maintaining the vacuum and/or inert environment throughout entire formation of the first thermoelectric film 101 and the first coating 110, when the latter is used, is certainly possible to implement, but might require additional resources. Moreover, processes such as printing may be quite difficult to integrate into an inert environment due to evaporation of solvents and/or binders from a drying ink layer. In this case it might be more practical to identify critical interfaces between layers which are formed without breaking vacuum and/or exposure to a contaminating environment. For instance, a layer of the first coating 120 and the first contact interface layer 106 may be deposited without breaking the vacuum and/or inert gas atmosphere between these deposition processes, whereas other layers may be formed without restriction to maintain vacuum and/or to protect against a contaminating environment. The above-mentioned layer of the first coating 120 may be the only one layer of the first coating 120, one of layers in a stack of layers of the fist coating 120, a top or a bottom layer in this stack. Selection of layers of the first coating 120 which are deposited without breaking the vacuum and/or inert gas atmosphere may depend on specific materials of these layers and/or tool park available for the deposition of these layers. Such an approach may be advantageous because it provides for a good quality of an interface between the first thermoelectric film 101 and the first and the second metal foil electrodes 111 and 112 and, on the other hand, it is compatible with the printing of the bulk layer of the first thermoelectric film 101.
After the forming of the first thermoelectric film 101 the first gap 131 is made to form the first and the second metal foil electrodes 111 and 112 from the first metal foil 110 (
The first gap 131 can be produced by micromachining, which makes it possible to produce gaps, in particular slits, in metals, in particular metal foils, preferably less than 1 mm wide. The micromachining includes physical machining like laser ablation (preferably photoablation), focused ion beam etching, or ion beam etching via a resist mask, when necessary. The micro-machining further includes chemical machining such as reactive ion etching via a resist or photoresist mask. The micromachining also includes mechanical machining such as cutting with a semiconductor wafer dicing tool or a micro-milling tool. The first gap can be produced using a combination of these techniques. For instance, a trench in the metal foil can be made by laser ablation, semiconductor wafer dicing tool, or a micro-milling tool, whereas the first gap 131 is completed by deepening the trench by ion beam etching. The trench may have a depth of at least 90% of the metal foil thickness.
The forming of the first thermoelectric film 101 may be performed such that a portion of the first metal foil electrode 111 and/or a portion of the second metal foil electrode 112 are devoid of the first thermoelectric film 101. Utilisation of the pressure-compaction of the powder or several powders for the forming of the entire first thermoelectric film 101 or its bulk layer allows additive manufacturing of the first thermoelectric film 101 such that the distal end portions of the first and the second metal foil electrodes 111 and 112 are completely devoid of the first thermoelectric film 101 or covered only by the first contact interface layer 106, when the latter is used. The powder or several powders can be provided only on a portion of the fist metal foil 110 for pressure-compaction, wherein the first gap 131 is made in this portion of the first metal foil 110 after the pressure-compaction is completed. When required, the portions of the first contact interface layer 106 on the distal end portions of the first and the second metal foil electrodes 111 and 112 can be removed, e.g., by laser ablation. In case the additive pressure-compaction is not used, i.e. the first thermoelectric film 101 is formed on the on the distal end portions of the first and the second metal foil electrodes 111 and 112, portions of the first thermoelectric film 101 on these distal end portions can be removed, e.g., by laser ablation, when the distal end portions devoid of the first thermoelectric film 101 are required.
In case the thermoelectric element 10 comprises the third and the fourth metal foil electrodes 113 and 114 in addition to the first and the second metal foil electrodes 111 and 112, the first powder sandwiched between the first metal foil 110 and a second metal foil 115 is pressure-compacted in the process step of the pressure-compacting of the first powder of the first thermoelectric material on the first metal foil 100, wherein the second side of the first thermoelectric film 101 is in direct contact with the second metal foil 115. This process step may be an extension of the process step of the pressure-compaction for the manufacturing of the thermoelectric element 10, which does not have the third and the fourth metal foil electrodes 113 and 114. Utilisation of the additional second metal foil 115 provided atop the first powder in the process of the pressure-compaction of the first powder on the first metal foil 110 enables manufacturing of the thermoelectric element having four metal foil electrodes 111-114. The process step results in a stack of the first metal foil 110, the first thermoelectric film 101, and the second metal foil 115, wherein the first metal foil 110 is directly attached to the first side of the first thermoelectric film and the second metal foil 115 is directly attached to the second side of the first thermoelectric film 101 (
The first thermoelectric film 101 may comprise another first contact interface layer 107. One side of the other first contact interface layer 107 is in direct contact with the second metal foil 115 or its coating 125, when the latter is used. An opposite side of the other first contact interface layer 107 is in direct contact with the bulk layer of the first thermoelectric layer 101. The other first contact interface layer 107 may have the same composition as the first contact interface layer 106. The other first contact interface layer 107 may be formed in the same way on the second metal foil 115 or its coating 125 as the contact interface layer 106 is formed on the first metal foil 110 or its coating 120. In case one or both first contact interface layers 106 and 107 are used, the first powder is pressure-compacted to form the bulk layer of the first thermoelectric film 101.
The pressure-compacted first thermoelectric film 101 is directly attached to the first and second metal foils 110 and 115 or their coatings 120 and 125, if any of them or both are used. In case the first contact interface layer 106 is used on the first metal foil 110 the pressure-compacted bulk layer of the first thermoelectric film 101 is directly attached to the first contact interface layer 106 on the first metal foil 110 or its coating 120, if the latter is used. In case the other first contact interface layer 107 is used on the second metal foil 115 the pressure-compacted bulk layer of the first thermoelectric film 101 is directly attached to the other first contact interface layer 107 on the second metal foil 115 or its coating 125, if the latter is used. If both first contact interface layers 106 and 107 are used on the first and the second metal foils 110 and 115 the pressure-compacted bulk layer of the first thermoelectric film 101 is directly attached to these first contact interface layers 106 and 107. The pressure-compacting of the first powder not only binds the particles of the first powder together, but also binds these particles to the surface of the first metal foil 110 or a top layer (e.g., 120 or 106) on the first metal foil 110, if this top layer (e.g., 120, 106) is used, and to the surface of the second metal foil 115 or a top layer (e.g. 125 or 107) on the second metal foil 115, if this top layer (e.g., 125 or 107) is used. In case a layer stack is used instead of the bulk layer of the first thermoelectric film 101 and the layers of the stack are formed in separate pressure-compaction processes, the second metal foil 115 is used in the last pressure-compaction process to form the stack of the first metal foil 110, the first thermoelectric film 101, and the second metal foil 115. The process or processes of the powder pressure-compaction for manufacturing of the thermoelectric element 10 comprising four metal foil electrodes 111-114 may be performed by at least one of the following processes: hot pressing, hot pressing with ultrasonic assistance, roll-compacting, or roll-compacting with ultrasonic assistance and/or at elevated temperature. These processes may be performed in vacuum and/or inert gas atmosphere. The powder or the powders may be prepared and provided for the pressure-compacting in the same way for the manufacturing the thermoelectric element 10 having only the first and the second metal foil electrodes 111 and 112 and for the manufacturing the thermoelectric element 10 having four metal foil electrodes 111-114. The layers 120, 106, 107, 125 on the first and the second metal foils 110 and 115 may be formed using surface cleaning and layer deposition processes without breaking vacuum and/or exposing the surfaces the metal foils or layers thereon to oxidizing and/or contaminating environment as described above. The exposure of the cleaned surfaces of the metal foils or the surfaces of the layers deposited thereon to oxidizing and/or contaminating environment may be avoided prior to pressure-compacting of the first powder provided between these processes. This process integration may be implemented by performing the pressure-compacting in the inert atmosphere and using deoxidized and/or degassed powder.
After the forming of the stack of the first metal foil 110, the first thermoelectric film 101, and the second metal foil 115 (
The thermoelectric element 10 with four metal foil electrodes 111-114 may be manufactured such that distal end portions of the metal foil electrodes are devoid of the first thermoelectric film 101 or thickness of its portions on the distal end portions is reduced in comparison to the central portion of the first thermoelectric film 101 bridging the first and the second gaps 131 and 132. This may be implemented by additive forming the first thermoelectric film 101. For example, the first powder for forming the first thermoelectric film 101 or its bulk layer may be provided on a predefined area on the first metal foil 110. In case the first thermoelectric film 101 is formed on the distal end portions of the metal foil electrodes 111-114, the portions of the first thermoelectric film 101 on the distal end portions may be removed by laser ablation, preferably by photoablation. In this case the laser beam is oriented in Y direction to remove portions of the first thermoelectric film 101 sandwiched between the pairs of the distal end portions of the metal foil electrodes 111-114.
A method of manufacturing of the thermoelectric element 20 employing p-n or p-i-n junction is based on the method of manufacturing of the thermoelectric element 10 comprising the four metal foil electrodes 111-114. In contrast to the method of the manufacturing the thermoelectric element 10 comprising four metal foil electrodes 111-114, a second powder of a second thermoelectric material is sandwiched between the first thermoelectric film 101 and a second metal foil 115. Put another way, the second powder is provided atop the first thermoelectric 101 film and the second metal foil is provided atop the second powder. The second powder may be provided on the first thermoelectric film 101 in the same way as the first powder is provided on the first metal foil 110. In particular, the second powder may be provided in a dry form on the first thermoelectric film 101 or an ink containing the second powder may be printed on the first thermoelectric film 101. The forming of the second thermoelectric film 102 comprises pressure-compacting the second powder sandwiched between the first thermoelectric film 101 and the second metal foil 115. The first thermoelectric film 101 can be formed on the first metal foil 110 in the same way as in the method for manufacturing the thermoelectric element having only two metal foil electrodes 111 and 112 (
The second metal foil 115 may have a second coating 125, which is in direct contact with the second thermoelectric film 102. The second coating 125 may have a different composition as the first coating 120 because these coatings 120 and 125 are in direct contact with thermoelectric films 101 and 102 having different conductivity types. The layer or layers of the second coating 125 are selected in accordance with the criteria mentioned above. The second coating 125 may comprise one or more of the following layers: an adhesion layer, a diffusion barrier layer, a work function setting layer, or an interface layer for reduction of a thermal and/or an electrical resistance between a metal foil electrode and a thermoelectric film. Specific examples of these layers are provided above. In case the second coating 125 comprise more than one layer, these layers are stacked on top of each other. The layer or layers of the second coating 125 may be formed using CVD and/or PVD.
The second thermoelectric film 102 may comprise the second contact interface layer 108. One side of the second contact interface layer 108 is in direct contact with the second metal foil 115 or its coating 125, when the latter is used. An opposite side of the second contact interface layer 108 is in direct contact with the bulk layer of the second thermoelectric layer 102. The second contact interface layer 108 may have the same composition as the first contact interface layer 106 of the thermoelectric element 10 having the second thermoelectric film 102 instead of the first thermoelectric film 101. The second contact interface layer 108 may be formed in the same way on the second metal foil 115 or its coating 125 as the contact interface layer 106 is formed on the first metal foil 110 or its coating 120 in the method of manufacturing of the thermoelectric element 10 having the second thermoelectric film 102 instead of the first thermoelectric film 102. In case the second contact interface layer 108 is used, the second powder is pressure-compacted to form the bulk layer of the second thermoelectric film 102.
As mentioned above, the first thermoelectric film 101 may comprise the first junction interface layer 103 and/or and the second thermoelectric film 102 may comprise the second junction interface layer 104. Any one or both of these layers may be formed in a corresponding deposition process, e.g. CVD, PVD. The surface for deposition of any of these layers may be cleaned, e.g., by plasma cleaning or ion beam cleaning. Moreover, all these cleaning and deposition processes may be performed without breaking vacuum and/or exposing the cleaned surface or the surface of the deposited layer to an oxidizing and/or contaminating environment. It is preferred that the second junction interface layer 104 is deposited immediately after the first junction interface layer 103 without breaking vacuum and/or exposing the surface of the first junction interface layer 103 to oxidizing and/or contaminating environment (
The pressure-compacted second thermoelectric film 102 is directly attached to the first thermoelectric film 101 and the second metal foil 115 or its coating 125, if the latter is used. In case the second contact interface layer 108 is used on the second metal foil 115 the pressure-compacted bulk layer of the second thermoelectric film 101 is directly attached to the second contact interface layer 108 on the second metal foil 115 or its coating 125, if the latter is used. In case a second junction interface layer 104 of the second thermoelectric film 102 is used on the first thermoelectric film 101 the pressure-compacted bulk layer of the second thermoelectric film 102 is directly attached to the second junction interface layer 104. If the second contact interface layer 108 and the second junction interface layer 104 are used, the pressure-compacted bulk layer of the second thermoelectric film 102 is directly attached to these interface layers 108 and 104. The pressure-compacting of the second powder not only binds the particles of the second powder together, but also binds these particles to the surface of the second metal foil 115 or a top layer (e.g., 108 or 125) on the second metal foil 115, if this top layer (e.g., 108, 125) is used, and to the surface of the first thermoelectric film 101 or the second junction interface layer 104, if the latter is used. In case a layer stack is used instead of the bulk layer of the second thermoelectric film 102 and the layers of the stack are formed in separate pressure-compaction processes, the second metal foil 115 is used in the last pressure-compaction process to form the stack of the first metal foil 110, the first thermoelectric film 101, the second thermoelectric film 102, and the second metal foil 115. The pressure-compacted first thermoelectric film 102 or its bulk layer are planar. The planar second thermoelectric film 102 or its planar bulk layer may be structured at later manufacturing steps. At this stage of manufacturing the first metal foil 110 and the first side of the first thermoelectric film 101 have a planar interface, the second side of the first thermoelectric film 101 and the first side of the second thermoelectric film 102 have a planar interface, and the second side of the second thermoelectric film 102 and second meta foil 115 have a planar interface. All these planar interfaces are disposed in respective parallel flat planes and the interface between the first and the second thermoelectric films 101 and 102 is disposed between the interfaces between the metal foils 110 and 115 and the respective thermoelectric films 101 and 102.
The process or processes of the powder pressure-compaction for manufacturing of the thermoelectric element 20 may be performed by at least one of the following processes: hot pressing, hot pressing with ultrasonic assistance, roll-compacting, or roll-compacting with ultrasonic assistance and/or at elevated temperature. These processes may be performed in vacuum and/or inert gas atmosphere. The powder or the powders may be prepared and provided for the pressure-compacting in the same way for the manufacturing the thermoelectric element 10 having two or four metal foil electrodes 111 and 112 or 111-114 and for the manufacturing the thermoelectric element 20 employing a p-n or p-i-n junction. The surfaces of the first thermoelectric film 101 and the second metal foil 115 may be cleaned, e.g. by plasma or ion beam cleaning. Afterwards, the second powder may be provided for pressure-compacting between the cleaned surfaces such that they are not exposed to oxidizing and/or contaminating environment, wherein the powder for pressure-compacting may be deoxidized and/or degassed prior to its pressure-compacting. As a next step the second powder is pressure-compacted between the cleaned surfaces in vacuum and/or inert gas atmosphere. The second contact interface layer 125 and a layer or layers of the second coating 125 on the second metal foil 115 may be formed using a sequence of deposition processes, which are performed without breaking vacuum and/or exposing layer surface to oxidizing and/or contaminating environment prior to a deposition of a next one. The first layer in this sequence may be deposited on a cleaned surface, preferably by plasma or ion beam cleaning, without exposing the cleaned surface to oxidizing and/or contaminating environment prior to the layer deposition. It is preferred that the adjoining layers of the second contact interface layer 107 and the second coating 125 are deposited without breaking vacuum and/or exposing said layer of the second coating 125 to oxidizing and/or contaminating environment. The process integration may be implemented by performing the pressure-compacting in the inert atmosphere and using deoxidized and/or degassed powder, wherein the powder is pressure-compacted between surfaces which were not exposed to oxidizing and/or contaminating environment.
After the forming of the stack of the first metal foil 110, the first thermoelectric film 101, the second thermoelectric film 102, and the second metal foil 115 (
The thermoelectric element 20 with four metal foil electrodes 111-114 may be manufactured such that distal end portions of the metal foil electrodes are devoid of the first and the second thermoelectric films 101 and 102 or thickness of their portions on the distal end portions is reduced in comparison to the central portions of the first and the second thermoelectric films 101 and 102 bridging the first and the second gaps 131 and 132, respectively. This may be implemented by additive forming the first and the second thermoelectric films 101 and 102. For example, the first powder for forming the first thermoelectric film 101 or its bulk layer may be provided on a predefined area on the first metal foil 110 and the second powder for forming thermoelectric film 102 or its bulk layer may be provided atop the pressure-compacted first powder. In case the first thermoelectric film 101 is formed on the distal end portions of the first and the second metal foil electrodes 111 and 112 and/or the second thermoelectric film 102 is formed on the distal end portions of the third and fourth metal foil electrodes 113 and 114, the portions of the first and/or the second thermoelectric films 101 and 102 on the distal end portions may be removed by laser ablation, preferably by photoablation. In this case the laser beam is oriented in Y direction to remove portions of the first and/or second thermoelectric films 101 and 102 between the pairs of the distal end portions of the metal foil electrodes 111-114.
The stack of the first metal foil 111, the first thermoelectric film 101, the second thermoelectric film 102, and the second metal foil 115 (
In another alternative method for stack manufacturing the first powder is provided on the first metal foil 110 and the second powder is provided on the first powder. Afterwards the second metal foil 115 is placed atop the first powder. The first and the second powders sandwiched between the first and the second metal foils 110 and 115 are pressure-compacted by at least one of the following processes: hot pressing, hot pressing with ultrasonic assistance, roll-compacting, or roll-compacting with ultrasonic assistance and/or at elevated temperature. As a result, the stack of the first metal foil 110, the first thermoelectric film 101, the second thermoelectric film 102 the second metal foil 115 is formed. Preferably the first powder is provided by printing the first ink containing the first powder and the second powder is provided by printing the second ink containing the second powder on the annealed printed layer of the first ink, wherein the printed layer of the first ink is annealed to remove a solvent and/or a binder from the printed layer of the first ink. The printed layer of the second ink is also annealed to remove a solvent and/or a binder from it prior to the powder-compacting of the first and the second powders provided as the annealed layers of the respective first and second inks sandwiched between the first and the second metal foils 110 and 115. This method for stack manufacturing also includes optional steps for forming one or more of the following layers: the first coating 120, the second coating 125, the first contact interface layer 106, or the second contact interface layer 108, which are described above in more detail. In addition, the bulk layer of the first thermoelectric layer 101 may be formed as a stack of layers, wherein layers of the stack constituting the bulk layer of the first thermoelectric film 101 are formed by providing respective layers of annealed printed ink layers containing powders, which are stacked on top of each other. The same applies mutatis mutandis to the bulk layer of the second thermoelectric film 102 when it is implemented as a stack of layers. In both cases all annealed printed ink layers for forming the first and the second thermoelectric layers 101 and 102 are pressure-compacted in one process of pressure-compacting to form the entire stack of the fist metal foil 110, the first thermoelectric film 101, the second thermoelectric film 102, and the second metal foil 115. Preferably each printed ink layer is annealed to remove a solvent and/or a binder from it prior to printing the next one.
The tool depicted in
The tools depicted in
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention.
In summary, the invention may be described by the following clauses:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 104 908.9 | Feb 2023 | DE | national |
